Field Trip 9: Owens Valley and the Eastern Sierra Nevada Mountains

Introduction

This field trip takes its participants to a land of extremes. You will drive along a valley with the greatest topographic relief when compared to the adjoining mountains on any in the lower 48 states.  You can see the tallest mountain, outside of Alaska, while at the same time being only 70 miles from the lowest point in the western hemisphere. You can walk amongst the oldest living trees and hike up the youngest volcanoes, which are part of what has been called the world’s youngest mountain range. You’ll view the site of one of the most colossal volcanic eruptions known and see evidence of Earth’s most recent Ice Age. All of this just a half-day away from L.A.!

   

This itinerary is written for a 3-day, 2-night excursion during the very late summer, early-mid fall, late spring, or earliest summer. Accommodations could be in one of the many hotels within Owens Valley, but camping is encouraged. There is a multitude of campgrounds available, many of which are first-come-first-served and others that require reservations. I’ve had excellent experiences at the McGee Creek campground and a colleague loves using Brown’s Town campground, which might be a good option for novice campers. In any case, I think it’s best from a logistics standpoint to camp close to or north of Bishop. Here’s one of many internet resources for camping options: camping in Owens Valley and Inyo County. Links to an external site. I also like this comprehensive and easy to use book on camping in California, California Camping. Links to an external site.

Utilizing a charter bus is highly recommended for this trip. The bus will keep everyone together and prevent trailing vehicles from lagging behind or getting lost. Charter busses should be equipped with a microphone, which will allow you to communicate the suggested “En Route Talking Points” and will also have ample room for camping gear in the undercarriage. All stops outlined in this chapter are accessible by charter bus. When reserving the bus emphasize that the driver should be experienced and comfortable with the daily itinerary outlined in this chapter and that the driver will need accommodations for each night of the trip. At the end of each day, be sure to communicate to the driver the next morning's pick up time and to get their cell phone number.

Accessing Devils Postpile National Monument (Day 2, Stop 5) requires some pre-planning and includes restrictions to consider. Devils Postpile is open at the earliest Memorial Day, but typically mid-June through mid-October; but this timeframe is weather dependent. A shuttle bus (Reds Meadow) transports visitors into Devils Postpile from the adventure center at Mammoth Mountain starting at 7:30 am. Tickets can be purchased at Mammoth Mountain Adventure Center. More information can be found with the Reds Meadow Shuttle. Links to an external site.  

If you wish to enter Devil's Postpile with a charter bus, you can do so with restrictions:

• Call 760-924-5505 one month beforehand to inform officials at Devils Postpile of your group’s visit
• Upon arrival at the Minaret Vista kiosk, you must present documentation that demonstrates your group's affiliation with a school or academic institution and a summary of the purpose of your visit written on official letterhead from your academic institution (contact Inyo National Forest Supervisor's Office at 760-873-2400 to confirm, as policies do change)
• Saturday and Sunday only
• If your vehicle is 25 feet or longer then you’ll need a special use permit: National Park Service Special Use Permit. Links to an external site.
• If your vehicle is longer than 25 feet then the bus must park at Reds Meadow after entering the national monument, see Devils Postpile National Monument map Links to an external site.
  • A shuttle service transports visitors every half hour to the Devils Postpile ranger station 10 am to 3:15 pm
• A vehicle 25 feet or less in length entering before 10 am or during weekdays can park at the Devils Postpile ranger station
• Drivers should be notified that the road is very narrow and windy in spots

Taking a group of students camping, many of which will be inexperienced with camping, will certainly require some preplanning. Assuming that your institution does not have a stockpile of camping equipment, here are few suggestions:

• Determine how many students have camping stoves or are certain they can acquire one before the trip
• Based on which students have stoves, assemble cooking groups around stove possessors; perhaps 6 students per group
• Once students have assembled into cooking groups, determine how many have tents. You may find that some groups do not have sufficient “tent space” for everyone, while others have excess. If so, consider rearranging students into different groups, in order to ensure that everyone will have a place in a tent.
• Determine who will provide a cooler, water, cooking gear, and cleaning supplies
• Ask students to come with a menu for the camping trip and to decide who is responsible for purchasing what and who will be cooking/cleaning and when. For a 3-day/2-night trip, they should plan for two breakfasts, lunches, and dinners. Lunch on day 1 should be prepared/purchased before they board the bus and on their person, NOT something that they will need to assemble while en route. Similarly, they should plan lunches that will transport in their daypacks for days 2 and 3. Also, remind them to bring fuel for stoves and keep meals simple. On one trip we had a group prepare a multi-course breakfast that resulted in delaying the entire class about ½ hour in the morning. Generally speaking though, I’m always impressed at how well my students do with the cooking.  
• If you find that you will not have enough camping stoves or tents, you may have to request the purchase of these reusable items through your department.
• Additional camping equipment:

sleeping bag	sleep pad	pillow
long underwear (base layers)	heavy jacket	windbreaker/rain jacket
beanie	long pants	sweater/sweatshirt
t-shirt	toiletries	gloves
flashlight	personal plate and utensils	coffee/hot chocolate mug
underwear	socks	medications

• Essential field gear:
  • Day pack
  • Field notebook/clipboard
  • Hat and sunscreen
  • Comfortable walking shoes – no flip-flops
  • Water
• Encourage students to try to keep things simple and to pack everything in one bag

Geography

Owens Valley runs along the eastern side of the Sierra Nevada Mountain Range (Sierras). At around 75 miles long and 5 miles wide, Owens Valley represents the westernmost valley of the Basin and Range geomorphic province. From the eastern side of the Sierras, the Basin and Range stretches across Nevada to the Wasatch Mountains in western Utah, with a topography characterized by a repeating sequence of roughly north-south oriented wide valleys (basins) separated by elongated mountain ranges (ranges). So persistent are the orientation and geometry of the basins and ranges, that this region was described by Charles Dutton, an important 19^th Century geologist, as an “army of caterpillars marching toward Mexico”.

The eastern boundary of the Basin and Range is the Sierra Nevada Mountains.   This massive mountain range is 400 miles long and 80 miles wide and contains the tallest mountain in the lower 48 states, Mt. Whitney, at 14,505 feet above sea level, as well as many other 14,000+ feet peaks. Owens Valley by comparison has an elevation of about 4000 feet above sea level, making for over 10,000 feet of elevation difference between the valley floor and the crest of the Sierras. This is the greatest topographic relief between two adjacent locations in the contiguous United States. For an even more dramatic contrast, Mt. Whitney is less than 90 miles from Death Valley, the lowest place in the western hemisphere, at -282 feet below sea level. 

The Sierras also form a topographic barrier to westerly-moving weather systems, which are forced up and over the mountains, where they lose their moisture as rain and snowfall along the western side and crest of the Sierras. The dry air then descends down the east side of the mountains, resulting in the semi-arid to arid high desert climate of the Basin and Range.

Geology

Owens Valley is a fault-controlled graben (meaning “ditch” in German) – typical of basins formed by crustal stretching within the Basin and Range geomorphic province. Faults bracket this block of crust on either side, structurally separating the Sierra Nevada and White-Inyo mountains along the western and eastern margins, respectively.

Map of Sierra Nevada Mountains, Owens Valley, Inyo Mountains, and the Panamint Range - Google terrain view map

Cross-section from the Sierra Nevada mountains to the Panamint mountain range. SNFF = Sierra Nevada Frontal fault; WIF = White Inyo Fault. Circled ✕ indicates crust moving away from viewer, while the bullseye symbol indicates crust moving towards. From Stevens et al 2013.

Recent earthquakes and fault scarps signify that Owens Valley continues to deepen, as well as slide horizontally relative to the growing mountains. Fossils and radiometric dates from minerals found in ancient lakebed deposits indicate that Owens Valley started to develop some 2.5-5 million years ago (Sharp and Glazner, 1997). All the while, streams eroding the surrounding mountains have transported and deposited their load of sediment onto the valley floor to a thickness of at least 10,000 feet. In the recent geologic past, during the last ice age, streams were more abundant, bringing so much water onto the valley that lakes, like Owens Lake, covered large areas of the valley floor. Volcanism is also part of the geologic evolution of Owens Valley; lava flows, ash deposits, and volcanic cones are common and offer more examples of natural extremes. For example, the Long Valley Caldera just beyond the northern end of the valley, represents the aftermath of one of the powerful eruptions in the history of North America, while the Inyo Domes, a chain of rhyolitic volcano domes, are considered by some to be the youngest mountain range in the world.  

The Sierra Nevada Mountains are the imposing western boundary to Owens Valley. The mountains are being actively uplifted along the Sierra Nevada Frontal Fault (SNFF), making the east side of the range essentially a large-scale fault scarp, called an escarpment. The Sierras can also be described as the Sierra Nevada Batholith; a batholith is a mass of intrusive igneous rock. A large body of magma, called a pluton, might cover 40 square miles if mapped on Earth’s surface. However, the Sierras measure 400 miles by 80 miles, making for a surface area of 30,000 miles… that is one huge pluton! Actually, the Sierras are a collection of many plutons, probably around 100, that rose as magma from deep in Earth's crust, think of blobs of "lava" in a lava lamp, coalescing and crystallizing, into a more-or-less continuous, blimp-shaped structure. This process began with the subduction of the Farallon Plate beneath the North American plate, which generated felsic-intermediate composition magma over the next 130 million years or so, slowly assembling the batholith at a depth of about 10 miles. Since, erosion of the overlying rock, isostatic uplift, and in the past 5 million years or so, tectonic uplift along the SNFF have acted to bring the batholith up to Earth’s surface. Today, we see the upper portion of this “blimp” of granitic rock exposed as a mountain range.

Starting around 2.5 million years ago, Earth entered its most recent ice age, the Quaternary Ice Age. During this time, the climate has cyclically cooled and warmed, called glacial and interglacial periods. During glacial periods, glacial erosion played a major role in shaping the topography of the Sierras; since the last glacial period ended a little less than 12,000 years ago, the glacial landforms are still very “fresh”, as there hasn’t been much time for weathering and stream erosion to wear them down. Today, the Sierras offer a wonderful opportunity to observe many classic glacial erosional landforms, including: U-shaped valleys, cirques, tarns, horns, arêtes, and hanging valleys. As the glaciers flowed out of their valleys and the climate once again warmed, melting and with it deposition occurred, resulting in the formation of distinctive glacial till landforms, in particular, lateral moraines. Most recently, the Sierras have been shaped by stream erosion and mass wasting. 

Learning Objectives

Through participation in this field trip students should be able to:

1. Recognize strata and sedimentary rocks
2. Identify volcanic (extrusive) rocks
3. Describe the texture of sedimentary rocks
4. Describe the texture of volcanic (extrusive) igneous rocks
5. Identify plutonic (intrusive) rocks
6. Describe the texture of plutonic (intrusive) rocks
7. Recognize rockfall in the field
8. Recognize badland topography
9. Identify a fault based on the disruption of strata or the ground surface
10. Using the relative position of the hanging wall and footwall, identify a fault as normal or reverse
11. Identify and draw a fault scarp
12. Recognize spheroidal weathering and describe how the process weathers rock
13. Describe how Ice Age climate and ecology was different than today
14. Identify erosional and depositional glacial landforms
15. Explain and provide examples of the effect of the Ice Age on eroding rocks and shaping the landscape  
16. Describe the significance of the Long Valley Caldera eruptions
17. Explain how a caldera forms
18. Identify volcanoes and volcanic features, such as, lava flows
19. Summarize the formation of a cinder cone
20. Describe the sequence of events that form a rhyolitic dome
21. Describe how tufa towers form
22. Describe how columnar joints form
23. Explain the selective distribution of the Bristlecone Pines
24. Summarize the history of the Los Angeles Aqueduct as it pertains to Owens and Mono lakes
25. Identify exfoliation and spheroidal weathering in the field
26. Explain the process of exfoliation and spheroidal weathering
27. Apply the law of superposition to determine the age of geologic events
28. Apply the law of cross-cutting relationships to determine the age of geologic events
29. Summarize the geography and geologic history of the Basin and Range

Key Vocabulary

Badland topography – a landscape with closely spaced drainages on steep slopes made of weakly cemented, fine-grained sediments; typically in arid climates with little vegetation.

Basalt - a common, fine-grained, mafic extrusive igneous rock. Typically black, weathers to a rust-brown; commonly vesicular.   

Basin and Range geomorphic province – continental rift zone comprising much of the southwestern United States where the topography is characterized by a series of roughly parallel fault-controlled mountains and valleys.

Batholith – a very large mass of intrusive igneous rock formed through the assimilation of numerous plutons.

Caldera – a massive crater or depression (> 1 km) caused by the collapse of a single volcano or several volcanic features after a large eruption has partially emptied the magma chamber(s).

Columnar jointing – fracturing in basaltic (usually) lava flows resulting in polygonal columns, typically 6-sided.

Coulee – very viscous lava flows of silica-rich lava that solidifies to form a thick, “blobby” mass that extends from a vent outward.

Exfoliation – mechanical weathering process where concentric fractures form curved sheets of rock, inches to a few feet thick, that break off, creating rock domes or rounded boulders.

Fault – a fracture in Earth’s crust along which movement has occurred.

Fault Scarp – a low, steep hill, caused by the vertical offset of the ground surface by movement along a fault.

Felsic – a term used to describe igneous rocks rich in silica and light-colored minerals like feldspar and quartz.

Graben – a block of crust down-dropping along faults resulting in forming a wide valley.

Glaciation – a period of time during an ice age when glaciers are growing and actively eroding.

Lateral moraine – eroded rock along the sides of a glacier that form low parallel hills after a glacier has retreated.

Law of crosscutting relationships – a geologic feature is always younger than the geologic body across which it cuts.

Law of superposition – in a sequence of sedimentary strata or volcanic rock, younger rock is atop older; i.e. each bed (sedimentary stratum) is younger than the bed beneath, but older than the bed above.

Metamorphic rock – a rock that has been altered from a pre-existing rock by heat, pressure, and/or hot fluids.

Normal fault – one of two types of vertical faults, where the hanging wall blocks slide down the fault surface relative to the footwall block in response to tensional stress during extension of the crust.

Obsidian - a felsic, glassy, extrusive igneous rock.  Typically black in color and exhibit conchoidal fracturing.  

Pleistocene – an Epoch of geologic time, beginning about 2.6 million years ago and ending about 10,000 years ago during which time Earth has been in an Ice Age.

Pluton – a large, irregular shaped blob of crystallized magma.

Plutonic/Intrusive igneous rock – a rock that forms from the crystallization of magma.

Pumice - a felsic, extrusive igneous rock with frothy/vesicular, glassy texture. Typically gray in color.  

Pull-apart basin – a wide valley that forms from tensional stress, e.g. graben.

Rhyolite - a fine-grained, extrusive felsic igneous rock. Pink, pale-gray, or pale-green in color. 

Sag pond – a type of pull-apart basin that fills with water to form a small lake.

Tuff (a.k.a. rhyolitic tuff) - a felsic rock with a fragmented texture of small rock fragments and possibly fine crystals. Commonly pink, light gray, or pale-pink in color.     

U-shaped valley – a valley formed by glacial erosion that has a “U” shape in cross-section.

Pre Field Lesson

Due to the extensive and varied curriculum to be covered over this three-day trip, I would strongly encourage dedicating a class session or two to introducing or reviewing the topics to be covered. Using part of the class session to discuss camping basics, equipment, clothing, etc., and to organize students into cooking groups is also a good idea. I also take this time to inform my group of the follow-up assignment and assessment (see the end of this chapter). In particular, they should be notified that they are expected to take photographs at each stop and record notes in their notebooks.

Pre Field Questions

1. Using the “Geology” section above, summarize in one paragraph the geology of the Sierra Nevada Mountains and Owens Valley.
2. What feature of sedimentary rocks makes them easily recognizable in the field?
3. Make a cross-sectional drawing of a normal fault; label the hanging wall and the footwall.
4. When was the last Ice Age? When did the last glacial period end?
5. What is spheroidal weathering and what type of rock does it typically affect?
6. How does the rock tuff form?
7. Describe how calderas can form.
8. How do lateral moraines form?
9. Compare and contrast the composition of the common igneous rocks basalt, rhyolite, tuff, obsidian, and pumice.
10. Summarize the geologic history of Devils Postpile National Monument; use the National Park website for the information: Devils Postpile National Monument. Links to an external site. Scroll down and start with “The Postpile begins as a lake of lava”.  

En Route Talking Points: I-605 north, I-210 west, CA-14 north

• I-605 north
  • The 605 takes us across part of the Los Angeles Basin. This incredibly deep basin formed from roughly 16 million to about 1 million years ago as tectonic forces slowly peeled the Transverse Ranges away from the Peninsular Ranges, rifting open a series of basins. The sea flooded these pits as they slowly opened, meaning what is today the metropolis of Los Angeles and Orange counties were once at the bottom of the Pacific Ocean. All the while, sediment being eroded from the continental highlands filled these depressions with silt, sand, and gravel, up to 6 miles in thickness.
  • San Gabriel River
    • The San Gabriel River Freeway (formal name for I-605)
      • Follows a path of least resistance from river erosion
      • River erosion creates natural pathways
      • Pathways become footpaths
      • Footpaths become horse trails
      • Horse trails become thoroughfares
      • Thoroughfares become highways
    • River transports sediment from the San Gabriel mountains to its base level, the Pacific Ocean
    • Whittier Narrows water gap. The San Gabriel River and Rio Hondo River, just to the west, have created the Whittier Narrows by eroding faster downward than the hills have been uplifted, resulting in carving a topographic saddle, a “water gap”, 2 miles wide and 800 feet deep, bisecting the Puente Hills into 2 parts: the Montebello Hills to the west and Whittier Hills to the east. For a more detailed description read the excellent discussion in Geology Underfoot in Southern California, “Vignette 9 – A Boon to Communication, The Whittier Narrows”
  • Whittier and Puente Hills (east of the 605) are being actively uplifted along the Whittier fault, which runs along the base of these hills; this fault is active as evidenced by the recent Whittier (1987, M 5.9), Chino Hills (2008, M 5.5), and La Habra (2014, M 5.1) earthquakes.
  • Montebello (Repetto) Hills (west of the 605)
    • Western extension of Puente Hills
    • Like Puente Hills, the Montebello Hills are made up of steeply tilted, south-dipping sedimentary rock that is typical of sediment in the LA Basin: mudstone, siltstone, sandstone, and conglomerate
  • On a clear day point out the San Gabriel Mountains making up the northern skyline and its highest peak, the 10,064 feet tall Mt San Antonio, a.k.a. Mt Baldy.
  • San Gabriel Mountains
    • Mountains at northern end of the 605 freeway
      • Part of the Transverse Mountain Range, which also includes the Santa Susana, Santa Monica, and Santa Ynez Mountains the Northern Channel Islands to the west, and the San Bernardino Mountains and Little San Bernardino Mountain, including Joshua Tree National Park, to the east 
      • Compressional tectonic forces have rapidly uplifted the San Gabriel Mountains past 5 million years
        • Could be growing as fast or faster than the Himalayan Mountains (Prothero, 2011), at a rate as fast as 70 feet per 1000 years (Sylvester and Gans, 2016)
        • Rapid uplift evidenced by very deep, steep canyons, like Arroyo Seco or Big Tujunga Canyon and triangulated ridges
        • Mountain range is being uplifted along 2 faults, the San Andreas fault along the north side and the Sierra Madre-Cucamonga fault zone along the south side
          • Sierra Madre fault zone
            • Runs along the foot of mountains
            • Has facilitated as much as 10,000 feet of vertical uplift of the crust, which is today expressed as the San Gabriel Mountains
            • Associated the San Fernando fault that produced the 1971 Sylmar earthquake
          • Contains metamorphic rock as old as 1.7 billion years, as well as Proterozoic plutonic rocks; these were intruded by magma of diorite to granite composition that was generated by subduction of the Farallon Plate during the Mesozoic time
        • After passing the I-10 and shortly before arriving at the I-210 interchange watch for deep pits on either side of the freeway
          • Gravel pits mining alluvium being shed off of the San Gabriel Mountains
          • Gravel used for concrete and roadways
          • Water in a pit means it is deeper than the water table (depth to groundwater)
• I -210 west
  • Sierra Madre fault zone
    • Runs along the foot of mountains
    • Has facilitated as much as 10,000 feet of vertical uplift of the crust, which is today expressed as the San Gabriel Mountains
    • Associated with the San Fernando fault that produced the 1971 Sylmar earthquake
  • The foothills are a series of coalesced alluvial fans that formed as the San Gabriel Mountains were uplifted, weathered, and eroded by streams; when the streams flow out of narrow mountain canyons, they slow and lose their ability to transport their sediment load, resulting in deposition and the formation of alluvial fans
  • Many of these stream channels are dammed where canyons open up, creating “catch flow basins” that trap or at least slow the dangerous boulder-sized clasts contained in inevitable debris flows
• Continuing on the I-210 west at the CA-134 interchange, look for “benched” road cuts, a common practice used to increase slope stability
• Driving through Sylmar takes one past the epicenter of the 1971 magnitude 6.5 Sylmar earthquake that caused over a billion dollars in damage and 65 deaths, mostly from the collapse of the Olive View Hospital
• Los Angeles Aqueduct
  • As the 210 mergers with I-5 look ahead and you should notice a long pipe-like feature coming down the hillside just to the right of the freeway

Los Angeles Aqueduct. 

• • • This is a chute for carrying water, baffled for aerating
  • One of three aqueduct systems bring water to the greater Los Angeles area, the other two being the California Aqueduct that delivers water from the western Sierra Nevadas, and the Colorado River Aqueduct that brings water from the Colorado River
  • Desgined by self-taught engineer William Mulholland to divert water from the Owens River and its tributaries to the burgeoning city of Los Angeles

William Mulholand. 

• • • • Water would be used to boost land values and profits for developers
    • Remarkable engineering feat considering it was desinged and built over 100 years ago, so water flows downhill over its entire length, requiring no pumps and only gravity to transport water from its source 235 miles to L.A.
    • Building the aquaduct necessitated some shady business dealings, violence, and even deaths
      • Residents of Owens Valley had plans to use the water from the Owens River to develop agriculture and livestock
      • Fred Eaton, a former mayor of Los Angeles and politically well-connected, used a contact in Owens Valley to, through deception, buy up land in Owens Valley and with it water rights to the Owens River
      • Mullholland and Eaton were also working behind the scences with a collection of friends and business partners to buy up cheap land in the San Fernando Valley, which would be made drastically more valuable once it was provided with a reliable water source
        • This story serves as part of the plot for the critically acclaimed 1974 movie Chinatown, starring Jack Nickolson: movie clip from Chinatown Links to an external site.
      • While completed ahead of schedule and under budget, the completion of the aqueduct consumed machines, mules, and men, with several construction-related deaths
      • Owens Valley residents rebelled upon learning that all the water of “their river” was being diverted to Los Angeles
        • In 1924 seventy armed Owens Valley men took control of an aqueduct gate and shut off the flow of water
        • In 1927 a 45-foot section was blown up
        • The uprisings were permanently squelched when Mulholland sent out machine gun armed horseback patrols with orders to shoot to kill anyone disturbing the aqueduct
• I-5/I-14 interchange
  • Some of the overpasses here collapsed during both the 1994 and 1971 earthquakes

• CA-14 (Aerospace Highway)
  • Placerita Canyon Road
    • Placerita Canyon earned its name and fame for the placer (gold deposited as sediment in a stream channel) deposits that were discovered here in 1842, six years before the Gold Rush began in the western Sierra Nevada Mountains.
  • Santa Clara River
    • Longest undammed river in southern California (Prothero, 2011) and significant in that its channel hasn’t been modified by human construction
    • Braided stream, common in the foothills of mountains
    • Multiple intertwining channels, weaving around channel bars
    • Ephemeral stream channel in that it is dry unless it has just rained
    • The dry channel is deceiving, because water is flowing in the subsurface as groundwater, which will eventually be utilized by communities downstream (Sylvester and Gans, 2016)
  • Vasquez Rocks
    • After passing Agua Dulce Road, look to the left (north) for spectacular stacks of tilted, red-brown sediment, jutting out of the ground
    • See chapter 4 for a more thorough description
  • Lamont Odet Vista Point
    • We are at the very edge of the Pacific Plate. Looking northward, our line of sight crosses the California Aqueduct, the San Andreas fault and the plate boundary with the North Ameican Plate, and Antelope Valley beyond.
    • Disappointlingly, the San Andreas fault is not an obvious gash, since it has been over 160 years since its last major break in southern California and erosion has “smoothed-out” disturbances, like scarps and ground cracks. Instead, the trace of the fault are the low hills, running northwest-southeast, through which highway 14 cuts through and lie on the opposite side of Lake Palmdale, continuing east into the mountains.
    • Lake Palmdale was originally a sag pond, a depression that collects water where there has been subsidence of the crust due to faulting. Here, the San Andreas fault is segmented, “stepping over” to create a pull-apart basin and sag pond – note how the arrows on either side of the pull-apart basin to pointing away from each other, creating tensional stress and subsidence. Recently, the sag pond was damned in order to store more drinking water for the cities of Paldale and Lancaster that spread out from the edge of the North American Plate before us.

• • • The California Aqueduct provides the greater Los Angeles area with a significant portion of its water. Constructed in the 1960s, it brings water from the western Sierra Nevada Mountains and transports it 700 miles, making it one of the longest aqueducts in the world. It was built above ground so repairs can be made more quickly after damaging San Andreas fault earthquakes; a matter of days vs. weeks or even months if the water were contained in underground pipes (Sylvester and Gans, 2016)
  • Palmdale Roadcut
    • The ridge through which CA-14 transects formed through intense compression of the relatively young, Pliocene Anaverde Formation. This sliver of crust is caught between two branches of the San Andreas fault: the San Andreas proper along the southern side and a secondary branch, the Littlerock fault, trending along the northern margin of the ridge, making the ridge an example of a squeeze block (see pages 18-19) or a pressure ridge (Sylveter and Gans, 2016). Excavations for geolgic study show that there is about 50 feet of right-lateral offset along the southside of the ridge.
  • Antelope Valley
    • Once through the Palmdale roadcut, you have crossed onto the North American Plate. “Antelope Valley”, containing the bustling communities of Palmdale and Lancaster, is a more appealing name invented by developers to describe what is actually the southwestern corner of the Mojave Desert.
    • As recently as a few tens of the thousands of years ago, lakes covered large parts of Palmdale and Lancaster. As our climate has warmed and dried, the lakes evaoporated.
      • Many archaeological sites occupy what would have been ancient lakeside beaches (Sylvester and Gans, 2016)
    • Rosamond Hills and Soledad Mountain (just north of community of Rosamond, west of the highway)
      • The colorful rocks that make up these hills are Miocene age rhyolitic volcanics, which have been hydrothermally altered, adding to the coloring
      • Mined extensively for gold, silver, and radioactive minerals
      • Rock collectors have frequented this area for geodes, chalcedony, and opal
    • Garlock Fault
      • Trace is marked by the straight eastern mountain front of the Tahachapi mountains
      • One of the longest faults in California at 160 miles
      • An exception to the norm, in that it is a left-lateral strike-slip fault – most horizontal faults in southern California are right-slip faults
      • Offset drainages abruptly jump to the right when crossing the fault
    • El Paso Fault and El Paso Mountains
      • El Paso Fault
        • Runs along the foot of the El Paso Mountains
        • Branch of the Garlock Fault
        • Facilitating uplift of the El Paso Mountains

Google Earth image with approximated location of the Garlock fault. - Google Earth. 

• • • • El Paso Mountains
        • Contain Red Rock Canyon State Park
        • Many cuestas of colorful sedimentary rock separated by ephemeral stream channels
      • El Paso Mountains “Gorge”
        • Pass used by CA-14 through the El Paso Mountains
        • Formed by stream erosion, making it a water gap – note stream channel and stream terraces immediately to the right of highway

Prepare for stop 1, a little less than a 1.5 miles from the southern front of the El Paso Mountains.

Field Trip Stops  

Utilizing a charter bus is recommended for this multi-day trip. Having everyone contained in one vehicle will allow for lecturing and giving instructions while the bus is moving, making for efficient and effective instruction. Considering the long distances that need to be covered, a charter bus service is probably the safest means of transport and eliminates the possibility of losing any members of your group while in transit.

Stop 1 – Red Cliffs at Red Rock Canyon State Park

Addresses learning objectives:
1. Recognize strata and sedimentary rocks
2. Describe the texture of sedimentary rocks
7. Recognize rock fall in the field
8. Recognize badland topography
9. Identify a fault based on the disruption of strata
10. Using the relative position of the hanging wall and footwall, identify a fault as normal or reverse

Turn right from CA-14 onto the Red Cliffs access road, just after the “side road right” sign (|–).

Depart bus (vehicles) and assemble at northwest end of parking area. Bathroom in block building immediately south of parking area.

• Red Cliffs
  • Ask, What type of rock are the cliffs made of? – Sedimentary. How can we tell? – Strata. Strata are stack of individual sedimentary layers or stratum. Each stratum represents a more or less continuous period of deposition.
  • Use the Geography and Geology sections at the start of this chapter to introduce RRC
  • Cliff face also provides a good example of badland topography

Activity 1: Pair-up students and have them examine the texture of some of the cobbles and boulders near the base of the cliffs. Help them differentiate between fine-grained sedimentary rock and volcanic rock.

Activity 2: Have students come back to edge of parking area and ask them to point out any evidence of mass wasting – Rock fall should be evident.

Fault exposed at Red Cliffs. 

Walk back towards the highway and just around the western edge of the Red Cliffs so you’re standing in the wash. Direct students to look to the northwest, to where the buff-colored strata intersect the highway then look about 200 feet to the right, where a fault offsets strata.  

Activity 3: Ask students to identify the fault then make a simple sketch that shows the strata offset and identifies the hanging wall and footwall. Ask: Considering the position of the hanging wall relative to the footwall, what type of fault is this? – Normal

Cross-section drawing of a normal fault. 

Return to bus and continue north on the CA-14. Once the 14 joins US-395, continue for another approximately 19 miles to Fossil Falls.  

En Route Talking Points: CA-14 north to CA-395

• Leaving the El Paso Mountains and Red Rock Canyon you enter the southwest corner of the Basin and Range geomorphic province, in which Owens Valley is contained
• As you approach CA-178 west note the southern terminus of the Sierra Nevada off to the left (northwest)
• Once you’ve reached CA-178 east, the route to Ridgecrest and Inyo-Kern, you should be able to observe the distinctive gray hue of the Sierra Nevada granite
• As CA-14 merges into CA-395 you may be able to make out the dark brown basalt flows that drape the low-profile Coso Mountains off to north-northeast and Red Hill
• The Pleistocene age basalt flows of the Coso Volcanic Field and our next stop, Fossil Falls, are clearly visible when you reach the turnoff for Kennedy Meadows and 9 Mile Canyon Road
• Little Lake was a vital stopover for northbound travelers in the first half of the 20^th century, providing water, food, and bed for a journey that could take several days

Stop 2 – Fossil Falls

Addresses learning objectives:
2. Identify volcanic (extrusive) rocks
4. Describe the texture of volcanic (extrusive) igneous rocks
13. Describe how Ice Age climate and ecology was different than today
15. Explain and provide examples of the effect of the Ice Age on eroding rocks and shaping the landscape  19. Summarize the formation of a Cinder Cone

Exit at Cinder Road (~ ¼ mile past the brown wooden sign for Fossil Falls and just before the Red Hill cinder cone). Point out the volcano to your group. Proceed just over ½ mile, then turn right on the Fossil Falls access road and proceed to parking lot. Restroom is at southwest corner of lot; trailhead at southeast corner.

Red Hill cinder cone. 

Assemble group at trailhead for a geologic overview of Fossil Falls:

• Three separate basalt flows
  • 10-20,000 years old
  • 100,000 years old
  • 400,000 years old
• The youngest flows are from Red Hill
  • Red Hill is a cinder cone
    • Built through the eruption of lapilli-sized (think pea to golf ball) basaltic pyroclasts (blobs of lava) during one more or less single eruptive episode that would have lasted weeks to months, to even a few years
    • Near the end of the eruptive cycle, basaltic lava flows were released, intermingling with older flows
  • Fossil Falls is comprised of the 100,000 year old flow
    • Contains minerals of labradorite, augite, and inclusion of basalt glass
    • The lava flows represent the rapids and waterfall section of an ancient stream bed
      • Considering the degree of scouring and polishing of the resistant basaltic lava flows, the ancient river must have flowed with tremendous force and a tremendous load of sediment
      • About 10,000 years ago the stream was draining Queens Lake, an ancient pluvial (Ice Age) lake that formed during the cooler and wetter climates associated with glacial periods during the Pleistocene
    • Pot holes attest to highly erosive power of this ancient river

Return to CA-395 and continue north.

En Route Talking Points: CA-395 to Owens Lake

• Owens Valley subtly begins north of the Coso Mountains and gradually opens up to what one could call Owens Valley “proper”, at the south end of Owens Lake
• As you approach the small community of Grant, about 3 miles south of Olancha, look west for nice examples of alluvial fans
• After passing through Olancha and by the Crystal Geyser bottling factory look east for Owens Lake
  • Today, Owens Lake is a playa, a dry or seasonally dry lake

For the Owens Lake stop, I recommend choosing a safe spot to pull off of the highway then discussing its interesting history from your vehicle. Since highway 395 is situated higher than the lake depression, you should have a reasonably good vantage point from the shoulder of the highway, or from the highway itself, if you choose not to stop and discuss while you roll along. There are two places near the north end of the lake that offer a wide shoulder for a bus-sized vehicle, the first is about 16.5 miles north of the CA-395/CA-190 junction at Olancha, just past the sign for “Visitors Center 5 miles ahead”. The second shoulder pullout is about ½ a mile further north. Alternatively, one could circumvent the ancient shoreline of the lake by taking CA-190 from US-395, then north on CA-136 back to the 395, but this will add at least 15 minutes to your journey.

Stop 3 - Owens Lake 

Addresses learning objectives:
13. Describe how Ice Age climate and ecology was different than today
24. Summarize the history of the Los Angeles Aqueduct as it pertains to Owens and Mono lakes

• 30-50 feet deep until 1913
• During the peak of the last glacial period the lake was up to 300 feet deep
• It covered so much area that steam boats transported cargo back and forth
• From 1862-1917 extensive farmland developed around the lake
  • By 1912 sixty-two thousand acres were cultivated and 160,000 fruit trees had been planted
• Los Angeles started diverting water via the Los Angeles Aqueduct in 1913
• Lake was dry by 1926
• “Bathtub rings” of salt deposits show the lake levels of the not-so-distant past
  • should be visible at the north end of the lake

Continue north on US-395. If you choose to explore Stop 4, take the turn off for CA-136, then immediately turn into the parking lot for the Eastern Sierra Interagency Visitor Center.

Stop 4 – Eastern Sierra Interagency Visitor Center (optional)

• Restrooms
• Instructive exhibits
• Picnic tables
• Shade

Continue north on US-395 to the city of Lone Pine. Turn left (west) onto Whitney Portal Road and continue a little over half a mile, crossing over the Los Angeles Aqueduct (points will be deducted if you try to blow it up), to the paved pullout, just after a brown wood sign for “Alabama Hills Information”.

Stop 5 – Lone Pine Fault Scarp

Addresses learning objectives:
10. Using the relative position of the hanging wall and footwall, identify a fault as normal or reverse
11. Identify and draw a fault scarp

Park bus in the “parking” area (see map below). If you’ve arrived using higher clearance vehicles, like vans, you could drive the “dirt road” to the scarp. Walking from the parking area, you could take the “trail” about 100 feet then climb up and over low embankment to connect to the dirt road. You could also walk back down Whitney Portal Road then turn left on the dirt road; walk over the two drainages, then turn right (east) on the dirt road immediately after the 2^nd drainage. Proceed up to the 90^o left turn. At this point the scarp intersects the path you are on. Assemble group.

Cartoon map showing the location of the Lone Pine fault scarp.  

Activity 4: Ask students to point out fault scarp, estimate the height of the fault scarp then share their estimate with one other student.

Fault scarps represent the uppermost portion of the fault surface, which is exposed after a fault breaks in an earthquake. In order for a fault scarp to show on Earth’s surface there must be some component of vertical movement along the fault.

Question: Considering that Owens Valley is a fault-controlled graben that formed in response to Basin and Range extension, what types of faults should we expect to find? – Normal.

Cross-sectional drawing of a normal fault.

Here, we have a 15-20 feet tall fault scarp, along the Lone Pine fault, a branch of the Owens Valley fault zone (Sharp and Glazer, 1993). Question, “How strong of an earthquake would be needed to produce a 20 feet tall high scarp?” Careful geologic studies along this fault show the scarp to be the result of at least 3 earthquakes; the most recent being one of the three strongest recorded in California’s history, the 1872 Lone Pine earthquake estimated to be a magnitude 8 or stronger. Paleoseismic studies imply a recurrence interval for the Lone Pine fault of 3000-4000 years. Prompt: Now, let’s try to determine if the Lone Pine fault is indeed a normal fault…

Activity 5: Pair students and direct one to stand on top of the fault scarp and the other at the base of the fault scarp. Take care to use any preexisting trails to minimize degradation of the scarp.

Question: Are the students at the base of the scarp standing on the hanging wall or footwall block of the fault?

Questions: What type of fault do you think this is? – Normal. Is it possible that it also moved laterally in addition to moving vertically? – We can’t really tell from here, but let’s look around for more evidence.

Continue walking north along the road, keeping to the left when it forks, to the dry stream channel. Observe the overall color of the sediment. Continue northward across the channel to where the road ends at a roughly east-west trending road. Looking north, ask if there is any difference between the sediment in the channel ahead and the sediment from the last channel.

Question: Why is the sediment darker in color here? – Different source (Alabama Hills vs. Sierras from the first channel).

The geologic studies mentioned earlier included mapping of the shape and alluvium in this channel. The data collected shows that the Lone Pine Fault has offset this channel to the right 35-40 feet.

Question: What does this tell us about the Lone Pine Fault? – It also moves laterally. This supports the belief among earth scientists that Owens Valley has developed through both sliding down along normal faults and horizontal sliding along “step-over” strike-slip faults (see Lamont Odet Vista Point in En Route Talking points above), which results in creating a pull-apart basin. Death Valley, the deepest basin in the western hemisphere, has formed similarly.

Return to vehicles then continue west on Whitney Portal Road for just under 2 miles to Movie Road

Stop 6 – Alabama Hills

Addresses learning objectives:
5. Identify plutonic (intrusive) rocks
6. Describe the texture of plutonic (intrusive) rocks
24. Summarize the history of the Los Angeles Aqueduct as it pertains to Owens and Mono lakes
25. Identify exfoliation and spheroidal weathering in the field
26. Explain the process of exfoliation and spheroidal weathering

A natural arch at Alabama Hills. 

Like Vasquez Rocks Natural Area and Red Rock State Park, the Alabama Hills are the site of many movies, television shows, and commercials. This dry, boulder-strewn landscape provides a quintessential western landscape and is easily accessible for Los Angeles based production companies.  

The Alabama Hills are comprised of two types of igneous rocks of two distinct geologic ages: 90 million year old granite and 150-200 million years old metamorphosed volcanic rock. The granite is of similar composition to the rock of the Joshua Tree National Park landscape and has weathered in a very comparable manner, which is why these two places look related.

Drive along Movie Road to take in and discuss the landscape or pull over at an inviting spot if you have the time and desire to get up close and personal with the rocks. A 1.5 miles drive from Whitney Portal Road will take you to Arch Rock Loop Trail, with a large parking area where a bus could turn around. I’d recommend the loop trail, especially hiking it in a clockwise direction, which will get you to the arch rock in about 10 minutes. From there you could discuss the weathering process of exfoliation, which is nicely exemplified on many of the boulders, as well as the weathering process of spheroidal weathering, which is helping to shape the granitic landscape of the Alabama Hills.      

Boulder showing exfoliation. 

Spheroidal Weathering

Weathering is the action of rock physically and chemically weakening and breaking down at or near Earth’s surface. At Alabama Hills the rounded hills and boulders of granite were shaped by spheroidal weathering, which involves several steps over thousands of years:

Rocks with joints. - CC

1. Before reaching Earth’s surface stresses acting on a batholith cause joints or sets of roughly parallel fractures in the body of rock. These intersecting fractures cut the rock into cubic shapes.
2. Through tectonic uplift and erosion the granite is brought close to Earth’s surface.
3. Acidic water infiltrating from Earth’s surface flows down and along the fractures, chemically reacting with feldspar in the granite and changing it into clay.
4. Because the fracture pattern creates cube-like blocks of granite, the corners of the cubes are preferentially weathered faster than the rest of the block – just like sucking on an ice cube will result in the cube becoming rounded – and the cubes of granite become more spherical
5. Once erosion exposes granite on Earth’s surface, the clay is easily washed away, leaving behind rounded hills and boulders of granite. The stripping away of clay and loose mineral grains is particularly effective when warming and drying climates reduce the density of vegetation, leaving soil and weathered rock more prone to water erosion.

Rock undergoing spheroidal weathering. - CC 

Spheroidal weathering at Alabama Hills. 

Before departing, be sure to point out Mt. Whitney, the tallest mountain in the U.S. outside of Alaska.

Mt. Whitney at arrow tip. 

Return to Whitney Portal Road and US-395. Continue north to Bishop. At the north end of town, the 395 makes a 90 degree turn to the left. From here it is about 11 miles to your next turnoff, Gorge Road (just after the brown, wood sign “Gorge Power Plant”). Turn right onto Gorge Road then a left where it “Ts” and proceed a little over 3 miles to another paved road that will take you east (right turn) towards Owens Gorge. After less than a ¼ mile, pull over on the shoulder just as the road curves back to the north. Exit vehicles and walk towards the edge of the gorge – urge students to exercise caution.

En Route Talking Points: CA-395 to Owens River Gorge

• If you are conducting this trip during the spring, you may be able to point out the difference in the amount of snow that has fallen on the Sierras vs. the White-Inyo Mountains to the east – a consequence of the rain shadow effect
• Good examples of alluvial fans coming off of the White-Inyo Mountains
• Just after the turnoff for Rovana, lateral moraines are visible coming out of Round Valley in the Sierras

Stop 7 – Owens River Gorge

Addresses learning objectives:
2. Identify volcanic (extrusive) rocks
4. Describe the texture of volcanic (extrusive) igneous rocks
16. Describe the significance of the Long Valley Caldera eruptions

Students at Owens River gorge.

• Situated on the flank of the Volcanic Tablelands, making up the northern end of Owens Valley
  • Volcanic Tablelands are 1000 feet high plateau made up of Bishop Tuff
    • Bishop Tuff
      • Pink, rhyolite tuff
      • Lithified ash fallout from the super volcanic Long Valley Caldera eruption, 760,000 years ago
    • The eruption expelled 150 cubic miles of ash, enough to bury all of Los Angeles county to a depth of 200 feet
  • The Owens River Gorge was formed catastrophically around 100,000 years ago, when the lake occupying the Long Valley caldera depression overtopped its southern rim, sending a torrent of water through the easily eroded Bishop Tuff

Activity 6: Have students walk around to collect, examine and make a sketch of a sample of Bishop Tuff.   The sketch should show the texture (pyroclastic) and any mineral (quartz) grains or rock fragments. Also include a description of the overall composition.

Walking up onto higher ground across the road one gets a great view of the Sierras and the lateral moraines coming out of Round Valley.

Activity 7: Ask students to point out the lateral moraines and discuss how they could have formed

Return to US-395, via the way you came in. Turn right, and continue north on the 395, up the Sherwin Grade to the top of the Volcanic Tablelands.

Stop 8 – Long Valley Caldera

Addresses learning objectives:
16. Describe the significance of the Long Valley Caldera eruptions
17. Explain how a caldera forms
18. Identify volcanoes and volcanic features, like lava flows

Portion of Long Valley Caldera. Mountains mark far edge of caldera.

Use the designated “Scenic Overlook” pullout for Lake Crowley, shortly after South Landing Road. Exit vehicle(s), take-in the majestic scene then discuss some of the dramatic highlights of one of the most destructive natural disasters known.  

Long Valley Caldera

• One of the largest calderas on Earth
  • 11 x 20 miles
  • Caldera walls about 3000 feet deep

Modified Google "terrain view" map showing major volcanic features of Long Valley and Mono Basin. - Google Maps

• Created by a super volcanic eruption 760,000 years ago
  • High silica rhyolite magma erupting from volcanoes and a series of vents partially emptied magma chamber(s), leaving them unable to support the weight of the overlying crust, which collapsed, triggering catastrophic eruption
  • Ash was blasted as high as 25 miles into the stratosphere, covering most of the western US, as far east as Nebraska and Kansas
  • Pyroclastic flows moved down Owens Valley, past present day Big Pine and up and over the crest of the Sierras
  • Ash fall was most dense around the eruption site, where it accumulated and consolidated into the pink, rhyolite tuff of the Bishop Tuff Formation (Stop 7 above), building up the 1000 feet high plateau upon which we stand, known as the Volcanic Tablelands
  • Immediately following the catastrophic eruption, the caldera was as much as 2 miles deep (Sharp and Glazner, 1987)
    • Ash fell back to Earth, filling about 2/3 of the pit
    • Since the eruption, thick rhyolite domes have grown within the caldera, including Mammoth Mountain, 200,000 years ago
  • Recent geologic activity reminds us that magma is still present
    • In 1980, four Mag 6.0 earthquakes in Mammoth Lakes area
      • 2 feet of ground swelling
      • 1990 earthquake swarm

This is probably a good place to call it a day and head to your campground or hotel. Since McGee Creek campground was mentioned at the start of this chapter, directions follow: From the Lake Crowley “scenic overlook” continue about 2 miles north on camping US-395. Turn left onto McGee Creek Road and head south towards the foothills. The road will wind its way up and around a lateral moraine before dropping down to the campground access road (~ 2 miles from US-395). It’s a narrow road, but navigable by charter bus.

Day 2, Stop 1 – McGee Creek Campground

Addresses learning objectives:
9. Identify a fault based on the disruption of strata or the ground surface
10. Using the relative position of the hanging wall and footwall, identify a fault as normal or reverse
11. Identify and draw a fault scarp
14. Identify erosional and depositional glacial landforms
15. Explain and provide examples of the effect of the Ice Age on eroding rocks and shaping the landscape  
16. Describe the significance of the Long Valley Caldera eruptions
17. Explain how a caldera forms
18. Identify volcanoes and volcanic features, like lava flows
28. Apply the crosscutting relationships to determine the age of geologic events

After you choose a lecture spot that won’t disturb other campers, you can address the lateral moraines of the Hilton Creek fault scarp:

• Lateral moraines are the hills bracketing the campground
  • Formed as a glacier receded from this valley near the end of the last glacial (Tioga) period
• Hilton Creek Fault scarp
  • During the 1980 magnitude 6.3 earthquake, the lateral moraines were offset 2-6”, compounding the past displacement caused by the 1872 Lone Pine Fault quake
  • The scarp is most obvious in the western lateral moraine, near the south side of the campground

Hilton Creek fault scarp in western lateral moraine. 

Activity 8: Ask students to point-out the lateral moraines and discuss how they could have formed.

Question: What could they tell us about the climate here in the past?

Activity 9: Ask students to use the law of crosscutting relationships to determine the relative age of the fault scarp and the lateral moraine… Which came first?

Activity 10: Ask students to consider the geometry of the fault scarp, then make a cross-sectional drawing showing the fault offsetting the moraine. On the drawing, label the moraine, the hanging wall, the footwall, and draw and name the type (normal) of fault.

From the McGee Creek Road/US-395 junction, proceed north on the US-395 for about 29 miles to CA-120. Turn right onto 120 then drive about 3 miles to Mono Craters Road (just past the trail/hiking road sign). Turn left and proceed to the parking area for Panum Dome.

Day 2, Stop 2 - Panum Dome and the Mono-Inyo Craters 

Addresses learning objectives:
2. Identify volcanic (extrusive) rocks
4. Describe the texture of volcanic (extrusive) igneous rocks
18. Identify volcanoes and volcanic features, like lava flows
19. Describe the sequence of events that form a rhyolitic dome
27. Apply the Law of Superposition to determine the age of geologic events

After leaving vehicles assemble group at the trailhead to talk about the geologic story of Panum Dome. You may want to utilize the interpretive display near the trailhead.

Panum Dome

• Geologically speaking… Just formed!
  • Carbon-14 (¹⁴C) radiocarbon dating techniques were used to determine the age of vegetation trapped between ash layers, yielding an age for the first eruption of 700 years ago (Sharp and Glazner, 1997)

Activity 11: Create an illustration showing the ¹⁴C-dated vegetation between ash layers then explain how the Law of Superposition can be used to determine the age of the lava flows.

• Typical volcanic dome (rhyolite dome)
  • Initial eruption produces ash and pumice, building the dome
  • Explosion from central vent creates the crater and a ring of volcanic rock, mostly pumice (pumice ring); explosion probably caused by rising magma superheating groundwater triggering a phreatic (steam explosion) eruption
  • Once all the gas from the magma chamber has been exhausted thick, rhyolite lava oozes out like toothpaste to partially fill the crater, creating a resurgent dome of obsidian

East side of Panum Dome. 

• • While the resurgent dome was growing, another eruption blasted out the crater wall, sending fresh volcanic glass (obsidian) down into Mono Lake
  • The last bit of magma slowly oozed up through cracks in the hardened lava of the resurgent dome, making spires of obsidian that are especially visible if you hike the Plug Trail onto the resurgent dome

Resurgent dome with spires of obsidian. 

• • Panum Dome is unique in that some of the volcanic rock contains clasts of granitic and metamorphic rock (xenoliths) that were eroded from the Sierras; these pebbles were incorporated into the magma as it rose to the vent
  • Geologists hypothesize that Panum Dome is fueled by a dike connecting it to a larger magma chamber

You may wish to complete your field lecture atop the volcano, where you have a better view of Mono-Inyo Craters and coulees.

Mono-Inyo Craters

Mono-Inyo Craters

• Panum Dome is part of the Mono-Inyo Craters (see map under “Stop 8 – Long Valley Caldera” above)
  • Formed from silica-rich rhyolite eruptions 40,000-700 years ago
  • Comprised principally of obsidian and pumice
  • Three massive coulees or obsidian lava flows
  • Volcanoes are oriented in an arc, reflecting the shape of fracture that connects Earth’s surface to a magma source
  • Very active in recent time, erupting every 250-700 years
  • The most recent volcanic activity formed Paoha Island within Mono Lake about 200 years ago
  • One of Earth’s youngest mountain ranges, rising about 2000 feet above the adjacent plains of Mono Basin
  • Tallest peak, Crater Mountain, is 9,172 feet above sea level
  • Coulees
    • Very viscous lava flows of silica-rich lava that solidify to form a thick, “blobby” mass that extends from a vent outward
    • Three large coulees are expressed as steep-sided plateaus flanking the Mono Dome
    • From the top of Panum Dome, we see the front of “North Coulee” making up the steep northern slope of the Mono Domes, directly south across highway 120
    • North coulee is about 630 years old (Sharp and Glazner, 1997)

North coulee at base of northern flank of the Mono-Inyo craters.  

• • • Permanent ice is contained deep within some of the fractures
  • In 1941 construction of a 11.5-mile tunnel under the southern part of the Mono Domes was completed as part of the Los Angeles Aqueduct system. This tunnel carries water diverted from Rush, Walker, Parker, and Lee Vining Creeks and into the Owens River, then down to Los Angeles. This diversion deprives Mono Lake of water and by 1982 the lake level has dropped dramatically by 45 vertical feet. Concerned locals started the “Save Owens Lake” movement, which has since helped bring the lake level back up and restore its ecology.

Question: What type of rock is Panum Dome made of? Is this rock high or low in silica? – High. Is this rock high or low in iron/magnesium. – Low.  

Take Mono Crater Road back to CA-120, turn left (east) and proceed about 1.6 miles to the Mono Lake access road.   Turn left just after the sign for “Mono Lake South Tufa”. Alternatively, you could continue for an additional ¼ mile to a shoulder pullout on the left side of the road for a good vantage point of one of the coulees that flowed eastward from the Mono Domes.

Day 2, Stop 3 – Mono Lake and Mono Basin

Mono Lake.

Addresses learning objectives:
2. Identify volcanic (extrusive) rocks
4. Describe the texture of volcanic (extrusive) igneous rocks
18. Identify volcanoes and volcanic features, like lava flows
21. Describe how tufa towers form
24. Summarize the history of the Los Angeles Aqueduct as it pertains to Owens and Mono lakes
29. Summarize the geography and geologic history of the Basin and Range

Exit vehicles and give students a chance for a potty break. Escort group down main path to the Mono Lake shoreline. At some point assemble your group to provide a Mono Lake overview.

• Mono Lake occupies the low spot within Mono Basin
  • Mono Basin is situated within the Basin and Range geomorphic province
    • The Basin and Range is characterized by a repeating sequence of roughly north-south oriented wide valleys (basins) separated by elongated mountain ranges. The western margin is marked by Mono Basin and Owens Valley, while the eastern side is bound by the Wasatch Mountains in western Utah, and includes all of Nevada and portions of Arizona and New Mexico. The distinctive topography is the result of continental rifting that started acting on the crust of western North America 16 million years ago, significantly stretching and fracturing the crust into linear, north-south trending faults, along which blocks of crust down-dropped to form deep basins, while uplifted blocks have formed mountains. Today this region displays dramatic relief, with mountain ranges rising as much as 10,000 feet above basins, including the lowest spot and deepest basin in the western hemisphere: Badwater Basin, 282 feet below sea level in Death Valley, California.  
  • Mono Basin
    • Subsided approximately 6000 feet over the past 3 million years coinciding with the growth of the Sierras
    • Question: Why is it subsiding? – Down-dropping along faults.
  • Mono Lake
    • 700,000 years old
    • 60 times larger at its peak
    • 3 times saltier than the Pacific Ocean and 80 times more alkaline
      • The alkalinity was attested to by Mark Twain who, while traveling in this area, wadded-up his travel-worn clothing and submerged the wad into Mono Lake. When he returned a day later he found that his entire bundle of clothes had completely disintegrated due to the extreme alkalinity.
    • The islands are Paoha and Negit. Both were formed by very recent volcanic activity, the lighter-colored Paoha as recently as 200 years ago.  
      • Paoha was formed as eruptions beneath lakebed sediments pushed the sediments upwards to their present elevation above the lake surface.
      • Mark Twain recounted his misadventure to the island in his book Roughing It, when he and his companion were lured to the island by a tale that told of cold, bubbling, pure spring water. With empty canteens they took a boat to the island, only to find “nothing but solitude, ashes, and heartbreaking silence". If that wasn’t bad enough they had not moored their boat, which drifted out into the lake that contained "venomous water (that) would eat a man's eyes out like fire, and burn him out inside too”. Miraculously, a passing storm blew their boat close enough to shore that his companion was able to leap in so they could get back to the mainland.
    • Tufa Towers (note: there is an interpretive “pullout” along the main trail back to the parking lot which is a good spot to discuss the tufa towers)
      • Misshaped columns of limestone
      • Formed when the alkaline, carbonate-rich water of Mono Lake chemically reacts with calcium ions introduced to the lake water through fresh water springs issuing from the lake bottom:

Mono Lake tufa towers.  

• • • • • CO₃ + Ca = CaCO₃ (limestone)
        • Limestone precipitates around the spring, building up column of limestone (tufa tower) over time
      • Tufa towers are now well exposed due to recent lowering of the lake level

Activity 12: Have students summarize in written words or with an illustration the process of formation for the tufa towers

Return to CA-120, then turn left (south) onto US-395. Continue for just over 9 miles to Obsidian Dome/Glass Flow Road (just past green road sign for Obsidian Dome) and make a right. After about a mile, bear left at the intersection with the road for Hartley Springs Campground. Continue 0.4 mile for a turnout with an interpretive sign and nice view of the side of the dome. This might be worth a quick stop, but the final destination is another 0.3 mile further, just past the gated road to the top of the dome; bear left and park next to Obsidian Dome. From here you’ll walk to the top of Obsidian Dome.

Day 2, Stop 4 – Obsidian Dome

Addresses learning objectives:
2. Identify volcanic (extrusive) rocks
4. Describe the texture of volcanic (extrusive) igneous rocks
18. Identify volcanoes and volcanic features, like lava flows
19. Describe the sequence of events that form a rhyolitic dome

Before starting the short walk to the top of Obsidian Dome, instruct your group to stay on the trail and to walk carefully. The ground surface can be dangerously sharp due to obsidian shards.  

Google Earth image showing Obsidian, Glass Creek, and Deadman domes. 

Obsidian Dome is situated near the southern end of the Mono-Inyo Craters. Like Panum Dome at the north end of the mountain range, it is an excellent example of a very young rhyolitic dome, having formed along with two volcanoes to the south, Glass Creek and Deadman Creek, 600 – 1350 years ago (Sharp and Glazner, 1997; USGS, 2012). Because they erupted concurrently and are aligned topographically, it is thought that the magma source is a single, sheet-shaped dike, leading down to a larger magma body at depth. Furthermore, it’s been proposed that the infamous 1980 earthquakes that rocked the nearby community of Mammoth Lakes were triggered by the intrusion of a similar dike (Sharp and Glazner, 1997) in this volcanically active area.

These volcanoes started off spectacularly through phreatic eruptions, when rising magma superheated groundwater, triggering an explosive escape of steam, lava, and rock. Following the initial explosion, pyroclastic eruptions threw ash to pumice-sized particles in the air, building up the juvenile cones. After most of the gasses had been released through pyroclastic eruptions, the final stage of the eruption commenced with the extruding of viscous, rhyolitic lava that solidified to form the domes of obsidian and pumice.

Obsidian and pumice are the product of very silica-rich magma. Silica (SiO₂) readily bonds to other silica molecules, forming long chains that prevent other atoms from migrating to crystallization sites (imagine trying to lift a fork up through a large pot of cooked spaghetti). Consequently, if high-silica lavas cool rapidly, it may solidify before crystallization happens and the unbonded atoms are simply frozen in place, making volcanic glass. If the lava solidified without gasses, then you get compact obsidian; while the presence of dissolved gases can cause the lava to froth (think of the milk froth on a cappuccino) and solidify around abundant vesicles making pumice.

Activity 13: Have students examine (Carefully! The rocks can be quite sharp.) rocks to differentiate between pumice and obsidian, and to identify any minerals if present.  

Activity 14: Describe the effect silica has on the viscosity of magma/lava. How might silica contribute to the explosiveness of an eruption?

Return to CA-120, then US-395. Turn left (south) and drive nearly 6 miles to Mammoth Lakes Scenic Loop road and turn right, then proceed about 6 miles to CA-203, Minaret Road. Turn right, taking you up to the Minaret Summit kiosk for Devil’s Postpile National Monument. This 4.5 miles drive takes you past “Earthquake Fault” and the Mammoth Mountain ski resort. Both of which offer instructional opportunities. Earthquake Fault makes for a fun, relatively quick stop, while Mammoth Mountain will necessitate 2-3 hours and paying for a lift up to the summit. Excellent fieldtrip guides and geologic discussions for these optional stops are available in Geology Underfoot in Death Valley and Owens Valley, vignettes 26 and 27.

Day 2, Stop 5 – Devils Postpile and Minaret Summit Vista

Devils Postpile. 

Addresses learning objectives:
2. Identify volcanic (extrusive) rocks
4. Describe the texture of volcanic (extrusive) igneous rocks
7. Recognize rock fall in the field
13. Describe how Ice Age climate and ecology was different than today
15. Explain and provide examples of the effect of the Ice Age on eroding rocks and shaping the landscape  
18. Identify volcanoes and volcanic features, like lava flows
22. Describe how columnar joints form

Minaret Vista

If you are able to enter Devils Postpile using your own vehicle(s), be sure to stop at Minaret Summit Visit. To do so, take the road immediately to the right of the kiosk for Devils Postpile. This can be a short 10-15 minute stop or longer if you choose to utilize the picnic area for your lunch spot. Charter busses will likely need to drop off the group, as the parking area is small then return for pick up. From the vista you look across a wide, U-shaped valley that contains the Middle Fork of the San Joaquin River. The jagged peaks on the far side of the valley are called the Minarets; two of the most prominent peaks are Mount Ritter and Mount Banner, at 13,157 and 12,945 feet tall, respectively. The Middle Fork of the San Joaquin River is an important part of the watershed (a.k.a. drainage basin) for the western side of the Sierras, where it collects runoff, flows through Devils Postpile National Monument, then out across the San Joaquin (Central) Valley to its ultimate base level, the Pacific Ocean.

After arriving at the Devils Postpile Ranger station, you have an easy 0.4 mile walk to the base of the Devils Postpile. Once there, assemble your group in one of the small observation areas for your lecture (maybe walk up the trail a bit to find a good spot) or, if you’ve not had lunch, take a lunch break at the riverside bench, immediately west of the trail.

Start off your lecture with some questions: What type of rock is Devils Postpile? Allow students to inspect the texture of some of the columns. What’s going on here? Why the columns?

Activity 15: Have students first discuss with one another then write a quick hypothesis about how Devils Postpile formed.

Devils Postpile

• 100,000 years ago, lava flowed down this valley and solidified into this mass of basalt
• Question: Are basaltic lava flows low or high viscosity? – Low (fluid)
• Individual basaltic lava flows are typically thin due to their fluidity (recall how thick the coulees are)
  • Considering the cliff in front of us, was this flow thin or thick? – Thick
  • Why is this flow so thick? – Geologists imagine that this lava flow encountered a barrier as it flowed down the valley, causing it to pond, like a river that encounters a dam. Considering the age of the flow, the barrier might have been a glacial moraine that has since been removed by river erosion.
• Columnar jointing (fracturing in basaltic lava flows resulting in polygonal columns, typically 6-sided) has weakened the rock
• Gravity pulls the columns exposed on the cliff face down as a form of rock fall
• Why did columns form in this particular flow? – Call on students for their answers from the activity above.
  • There are two important characteristics of this lava flow that allowed the columns to form:
    • The lava flow was very thick, 100 feet or more, so it cooled slowly
    • The lava flow was homogeneous basalt and without vesicles (small holes)
  • The lava slowly cooled and solidified to rock
  • As the very hot rock mass continued to cool, it contracted
  • The stress on the rock mass from contraction was relieved by fracturing in a direction perpendicular to stress direction (imagine pulling each end of a piece of paper in opposite directions until it tears down the middle)
  • As these fractures intersected one another, they formed polygonal columns of basalt
  • Weathering agents, like frost wedging, have enlarged fractures over time and gravity has pulled down columns through the process of mass wasting, i.e. rock fall

Activity 16: Have students discuss and modify their descriptions about how the columns formed.

Now hike to the top of Devils Postpile. This is a short, but steep hike that offers some nice views and an opportunity to inspect the columns in cross-section, and to see evidence of glacial erosion (glacial grooves).

Students atop the columns of Devils Postpile.  Glacial grooves visible as lines trending left to right on foreground columns.

Activity 17: Pair up students and have them count and record the number of sides on 20 individual columns. How many sides are most common?

If you have more time and an enthusiastic group, you might want to consider hiking to Rainbow Falls, a little over 4 miles round trip from the base of Devils Postpile.   

End day 2.

Day 3 Stop – Ancient Bristlecone Pine Forest

Addresses learning objectives:
1. Recognize strata and sedimentary rocks
23. Explain the selective distribution of the Bristlecone Pines

An ancient bristlecone pine.  

The Ancient Bristlecone Pine Forest is located about 10,000 feet up in the White Mountains, the mountain range along the eastern margin of Owens Valley. It is generally accessible from Memorial Day to the end of October, but you’ll want to confirm accessibility ahead of your visit. Be prepared for cold temps and thin air!

If you’re returning to Los Angeles today, then I’d recommend getting started with your day as early as possible. Depending on where you’ve stayed the night, you’ll need to find your way to the intersection of US-395 and CA-168, just north of Big Pine. The turn off for the Ancient Bristlecone Forest is White Mountain Road, 12.6 miles east on CA-168 east. On your way up the mountains, look for exposures of some of the bedrock. Starting in the first “narrows” section, about 8 miles from the 395, you’ll see the 500 million year old, dark brown Campito Formation. The second and third narrows expose bluish limestone of the Poleta Formation.

Just after the sign for the Bristlecone Forest, turn left (northwest); the parking lot for Schulman Grove, which contains the ancient Bristlecone Pines, is a 10 miles drive from the highway. At 7.7 miles, make a quick stop at “Sierra View”, which aptly offers spectacular views of the Sierra Nevada Mountains.

"Sierra View" view.  

Once parked at Schulman Grove, walk back to the parking lot entrance and assemble on southeast corner, near the welcome sign. This makes for a good place to give an overview of the White Mountains and the importance of the geology as it relates to the Bristlecone Pine trees.

White Mountains

• Notably different than the Sierras – one could argue “drearier” in appearance, because:
  • Drier
    • Lie in the rain shadow of the Sierras
    • Less trees and no lakes
    • Less snowfall means there has been less glaciation
      • Peaks are more rounded and subdued than the sharp, dramatic, glaciated peaks of the Sierras
    • Rocks
      • Older and different lithology
        • 550 to 700 million years old
        • Mostly metamorphosed sedimentary rock
        • Darker in color – compared to the relatively bright granite of the Sierras
        • Well exposed in roadcuts along CA-168

Ancient Bristlecone Pines

• Oldest living trees in the world
  • The Schulman Grove contains 17 trees over 4000 years old and the oldest known single tree at 4845 years old (website: Rocky Mountain Tree-Ring Research), although another tree has unverified age of 5,068 years.
  • For comparison, the oldest giant Sequoias are around 1400 years old
• How can they live so long?
  • Very hardy – survive where other vegetation can’t
    • Low precipitation
    • Cold
    • Thin air
    • Persistent wind
    • Nutrient-poor soil…
  • Note the distribution of bristlecone pines:
    • Growing on slopes above us, but not in the valley opposite the road, which is covered in sagebrush. Why is this? Perhaps point out the color of the soil supporting the bristlecone pines vs. the color of the soil for the sagebrush.

Sage covers the left side of the slope, while bristlecone pines are growing on the right side.

Activity 18: Allow students to discuss the answer to your question. Perhaps walk amongst your group to facilitate this discussion.

Before answering this very important question, hike amongst the majestic bristlecone pines. There are a few trails, but the sake of time, fitness of typical students, and for instructional value use the “Discovery Trail”. Walk back through parking lot to the Discovery Trail trailhead, at the far northeast end. Before starting the hike, differentiate the bristlecone pine from another tree that you will see on the trail, the limber pine. The bristlecone needles are darker and grow in spirals around and along stems, while the limber pine needles are lighter green and cluster at the end of stems. For comparison, the tree in the middle of the parking lot circle is a limber pine; the tree on the left side of the pathway to the visitor center is a bristlecone pine (Sharp and Glazner, 1997).   The oldest bristlecone pines will look, well…old. They won’t have a full set of branches, but instead only few living branches. They have dead, jagged tops, and a thin strip of bark twisting around the tree up to the living branches.

Before starting the hike, it might be a necessary to allow for a potty break. Once everyone is ready to go, mention a few important notes for the hike:

• While admiring the bristlecone pines, without disturbing them in any way, consider the coloring and weathering of the rock and soil around the ancient trees
• Look out for an abrupt change to the coloring and weathering of the rock and soil
• Look out for an abrupt change to vegetation
• Don’t get too far ahead of the group, because there will be at least one lecture stop    
• Walk single-file to allow room for other hikers

The trail climbs through the edge of the bristlecone pine forest, but eventually emerges out onto a barren slope, mantled by brown, angular rocks. Choose a good spot for a lecture, perhaps starting with a few questions:

• Did you notice a change in the coloring or weathering of the rock and soil? – Yes, the rock/soil is darker and more angular here.
• How about the vegetation? – No bristlecone pines grown here.
• Let’s go back to the question we discussed before we started our hike: Why don’t bristlecone pines grow here and down in the valley below us? – Take/call on students for answers.
• Answer: the distribution of bristlecone pines is restricted by geology
  • Note the variations in color of the soil upon which the bristlecone pines are growing vs. the color of the soil that supports the sagebrush: white to very light brown vs. a more medium brown
    • Medium brown soil comes from the weathering of the blocky brown rock – sandstone of the Deep Springs Formation
  • Bristlecone pines would probably like very much to grow in the darker brown soil, found where we are standing and down in the valley, but cannot because the sagebrush outcompetes the bristlecone pine seedlings for water and nutrients, preventing them from growing
  • Instead, the bristlecone pines grow where other plants can’t – in the nutrient poor soil produced by the weathering of the Reed Dolomite
    • Dolomite is composed of magnesium calcium carbonate, which breaks-down to form a very alkaline soil (remember the extreme alkalinity of the carbonate-rich Mono Lake)
    • Sagebrush, like most all other plants, can’t grown in such alkaline soil
  • Generally speaking, geologists can use the distribution of different types of vegetation to estimate the distribution of rock units and the location of rock structures

Activity 19: Have students edit their answers to the question they discussed in activity 18.

Before returning home you might want to spend a little time in the visitors center.

Follow-up Activities

1. Multiple choice quiz or exam with a mix of question types, including essay responses.  
2. Students prepare a 5-10 minute PowerPoint (or other multimedia platform) presentation discussing a topic from the field trip. I like to utilize the downtime of the return trip for getting students started on this assignment. I’ll pass around a pad of paper and ask them to record their name and a topic they learned about. Examples include: geology of the Red Cliffs at Red Rock Canyon State Park, formation of Fossil Falls, spheroidal weathering and the Alabama Hills, history of Owens Lake, and the geologic story of the Long Valley Caldera. Once they’ve chosen a topic, I encourage them to utilize the time of the long bus ride home to compose an outline. For myself, I’ll use the time to modify any assessments I plan to give, in order to most clearly reflect the learning objectives covered or emphasized on the trip.  

Student presentations need to include photographs from the trip and content from their notes, as well as additional resources. In addition to teaching about their topic, the presentations should include an introduction and a summary, as well as a list of additional resources used. Text on each slide should be kept to a minimum; students should instead be encouraged to use note cards. Grading criteria should consider:

• Well organized slides with limited text and illustrative photos
• How authoritatively do students speak about their topic
• The use of additional resources to introduce relevant and interesting facts and/or interpretations of facts presented during the field trip
• Overall clarity of presentation

3. Photo journal. I do not use this as an assessment tool, but a colleague does so with great success. Students create a photo album with descriptions and discussions around their field trip photos.