Devils Postpile National Monument 

Geologic Resources Inventory Report 

Natural Resource Report NPS/NRPC/GRD/NRR—2009/160 

National Park Service 

U.S. Department of the Interior 

Natural Resource Program Center 
THIS PAGE: 

The dramatic columns of Devils Postpile are 

between 12 and 18 m (40 and 60 ft) tall and up to 

1.1 m (3.5 ft) in diameter. Seismic and weathering 

processes fracture the columns along joints. Broken 

columns litter the slopes beneath Devils Postpile. 

ON THE COVER: 

Top view of the 100,000 year-old columns of Devils 

Postpile. The columns are world-renowned and 

many form the ideal hexagonal shape. The 

striations and scratches are evidence that glaciers 

advanced over the columns, scouring their surface. 

National Park Service photographs. 
Devils Postpile National Monument 

Geologic Resources Inventory Report 

Natural Resource Report NPS/NRPC/GRD/NRR—2009/160 

Geologic Resources Division 

Natural Resource Program Center 

P.O. Box 25287 

Denver, Colorado 80225 

February 2010 

U.S. Department of the Interior 

National Park Service 

Natural Resource Program Center 

Denver, Colorado
The National Park Service, Natural Resource Program Center publishes a range of reports that 

address natural resource topics of interest and applicability to a broad audience in the National 

Park Service and others in natural resource management, including scientists, conservation and 

environmental constituencies, and the public. 

The Natural Resource Report Series is used to disseminate high-priority, current natural 

resource management information with managerial application. The series targets a general, 

diverse audience, and may contain NPS policy considerations or address sensitive issues of 

management applicability. 

All manuscripts in the series receive the appropriate level of peer review to ensure that the 

information is scientifically credible, technically accurate, appropriately written for the 

intended audience, and designed and published in a professional manner. This report received 

informal peer review by subject-matter experts who were not directly involved in the 

collection, analysis, or reporting of the data. 

Views, statements, findings, conclusions, recommendations, and data in this report are those of 

the author(s) and do not necessarily reflect views and policies of the National Park Service, 

U.S. Department of the Interior. Mention of trade names or commercial products does not 

constitute endorsement or recommendation for use by the National Park Service. 

Printed copies of this report are produced in a limited quantity and they are only available as 

long as the supply lasts. This report is available from the Geologic Resources Inventory website 

(http://www.nature.nps.gov/geology/inventory/gre_publications.cfm) and the Natural 

Resource Publications Management website (http://www.nature.nps.gov/publications/

NRPM). 

Please cite this publication as: 

Graham, J. 2009. Devils Postpile National Monument Geologic Resources Inventory Report. 

Natural Resource Report NPS/NRPC/GRD/NRR—2009/160. National Park Service, Denver, 

Colorado. 

NPS 120/100620, February 2010 

ii NPS Geologic Resources Division 
DEPO Geologic Resources Inventory Report iii

Contents

List of Figures .............................................................................................................. iv

Executive Summary ...................................................................................................... v

Introduction ................................................................................................................... 1

Purpose of the Geologic Resources Inventory ...........................................................................................................1

Regional Location and Geologic Setting.....................................................................................................................1

Formation of the Devils Postpile.................................................................................................................................2

Park History................................................................................................................................................................2

Geologic Issues............................................................................................................. 5

Column Collapse ........................................................................................................................................................5

Preservation of Glacial Features ................................................................................................................................5

Recurring Volcanism ..................................................................................................................................................5

Potential Research Projects .......................................................................................................................................6

Geologic Features and Processes............................................................................. 11

Devils Postpile..........................................................................................................................................................11

Glacial Features .......................................................................................................................................................11

Other Volcanic Features...........................................................................................................................................12

Rainbow Falls...........................................................................................................................................................12

Mineral Springs.........................................................................................................................................................13

San Joaquin River and Soda Springs Meadow ........................................................................................................13

Map Unit Properties .................................................................................................... 16

Geologic History.......................................................................................................... 23

Paleozoic Era (542 to 251 million years ago) ...........................................................................................................23

Mesozoic Era (251 to 65.5 million years ago)...........................................................................................................23

Cenozoic Era (65.5 million years ago to the present)...............................................................................................25

Glossary....................................................................................................................... 35

Literature Cited............................................................................................................ 39

Appendix A: Overview of Digital Geologic Data....................................................... 43

Appendix B: Scoping Summary................................................................................. 45

Attachment 1: Geologic Resources Inventory Products CD
iv NPS Geologic Resources Division

List of Figures

Figure 1. Location map of Devils Postpile National Monument. .....................................................................................6

Figure 2. The Sierra Nevada fault block.........................................................................................................................3

Figure 3. Basalt columns of the Devils Postpile. ............................................................................................................4

Figure 4. General stratigraphic column showing rock units exposed in Devils Postpile National Monument. ................4

Figure 5. Historical earthquake map of California ..........................................................................................................7

Figure 6. Seismicity of California showing earthquakes from 1990 to 2006...................................................................8

Figure 7. Glacial polish and glacial striations on the top of the columns at Devils Postpile National Monument............8

Figure 8. Long Valley Caldera and vicinity.....................................................................................................................9

Figure 9. Exposed ends of the columns at Devils Postpile National Monument...........................................................10

Figure 10. A hexagonal pattern is the ideal shape for columnar joints in basalt...........................................................10

Figure 11. Pothole Dome, a large roche moutonnée in Yosemite National Park .........................................................13

Figure 12. Rainbow Falls. ............................................................................................................................................14

Figure 13. Original channel of the Middle Fork of the San Joaquin River, Devils Postpile National Monument...........14

Figure 14. Iron from Soda Springs creates the orange color visible in mid to late summer..........................................15

Figure 15. The Middle Fork of the San Joaquin River meanders through Soda Springs Meadow. ..............................15

Figure 16. Geologic time scale.....................................................................................................................................27

Figure 17. Diagrams of general fault types. .................................................................................................................28

Figure 18. Late Cambrian paleogeographic map of North America. ............................................................................29

Figure 19. Early Mississippian paleogeographic map of southwestern North America ................................................30

Figure 20. Late Permian paleogeographic map of southwestern North America .........................................................31

Figure 21. Schematic drawings of subduction zones off the western margin of the United States. .............................32

Figure 22. Late Cretaceous paleogeographic map of North America...........................................................................33

Figure 23. Growth of the San Andreas Fault System...................................................................................................34
DEPO Geologic Resources Inventory Report v

Executive Summary 

This report accompanies the digital geologic map for Devils Postpile National Monument in 

California, which the Geologic Resources Division produced in collaboration with its 

partners. It contains information relevant to resource management and scientific research. 

This document incorporates preexisting geologic information and does not include new data 

or additional fieldwork.

Devils Postpile National Monument, established in 1911, 

lies southeast of Yosemite National Park in the Sierra 

Nevada of California. Although a relatively small western 

national monument, it contains world-renowned 

examples of vertical columnar basalt. Vertical columns of 

basalt are rare, requiring homogeneous lava to cool 

under exceptionally uniform cooling conditions. These 

columns of basalts—the “posts” for which the Devils 

Postpile was named—stand 12 to 18 m (40 to 60 ft) high 

and are up to 1.1 m (3.5 ft) in diameter. They formed 

100,000 years ago when lava flowed down the Middle 

Fork of the San Joaquin River, pooled in the valley, and 

cooled.

Significant geologic issues at Devils Postpile National 

Monument include:

• Column collapse

• Preservation of glacial features

• Recurring volcanism

Basalt column collapse is unpredictable, although most 

of the collapse is likely the result of ground-shaking 

caused by earthquakes. In 1980, three columns toppled 

following a series of four intense earthquakes 

(magnitudes 6.0 or greater on the Richter scale), as well 

as a swarm of lesser earthquakes that same year. These 

three columns had been leaning since at least 1909. In 

addition to ground shaking, the prying action of water 

that freezes in cracks between the columns may also 

contribute to column collapse.

Preservation of glacial polish, striations, and grooves on 

the polygonal tops of the columns provide evidence that

Pleistocene alpine glaciers flowed into this area. Rock 

collecting, which is not permitted in the park, and 

natural weathering processes have eliminated some of 

the glacial polish. Removal of these polished tops not 

only detracts from future visitors’ experiences, but also 

removes critical geologic evidence of glacial processes in 

Devils Postpile National Monument.

Hot springs, seismic activity, and carbon dioxide gas 

emissions suggest that the volcanoes in this region are 

not extinct. Active seismicity and ground deformation

characterize the Long Valley Caldera that lies northeast 

of Devils Postpile National Monument. Future volcanic 

activity may produce small- to moderate-volume 

pyroclastic eruptions, cinder cones, and lava flows.

Not all of the basalt columns are vertical. Because vertical 

columns require exceptionally uniform cooling 

conditions in homogeneous flows, many columns in the 

monument are tilted, and some display spectacular 

curved shapes.

In addition to the basalt of Devils Postpile, other volcanic 

features are present in the monument area. The 

Buttresses, a feature composed of the oldest volcanic unit 

in the park, resulted from lava that erupted from vents 

west of Devils Postpile National Monument. A lava flow 

composed of the volcanic rock rhyodacite is responsible 

for the cliff at Rainbow Falls, a 31-m (101-ft) waterfall 

and the highest waterfall on the Middle Fork of the San 

Joaquin River. Dense hard volcanic tuff from the 

catastrophic eruption that produced the 16- by 32-km 

(10- by 20-mi) Long Valley Caldera is exposed behind 

the old ranger cabin east of Reds Meadow. Remains of a 

10,000-year-old basalt flow and cinder cones are 

preserved at Red Cones, about 2.4 km (1.5 mi) southeast 

of Devils Postpile National Monument. 

When tectonic forces uplifted the Sierra Nevada in the 

Quaternary, the mountains were simultaneously being 

worn down by Pleistocene glaciation. Glaciers flowed 

down the Middle Fork several times, gouging out a Ushaped valley and leaving their marks on the rocks. 

Glacial polish, striations, and grooves are evidence of the 

erosive power of the glaciers. “Glacial erratics,” boulders 

carried by the glaciers, are strewn throughout the region 

and are most abundant on the high granite hills and 

ridges west of the Middle Fork. Glacially-carved cirque 

basins contain alpine lakes at the base of glacially-shaped

peaks.

Rocks in the Sierra Nevada record a history of tectonic 

change that occurred along the western margin of North 

America beginning as far back as the Paleozoic Era. 

Plutonic, volcanic, and sedimentary rocks were 

deformed and added to the continental margin as the 

North American continent overrode subducting slabs of 

oceanic lithosphere. In the Cenozoic, transpression

(plates colliding and sliding past each other) and strikeslip faulting (plates sliding past each other) generated the 

San Andreas Fault system. High heat flow continues to 

uplift the region today. Mineral springs, earthquakes, 

and volcanic activity that occurred as recently as 600 

years ago attest to the continued tectonic activity in the 

Devils Postpile region.
vi NPS Geologic Resources Division

The glossary contains explanations of many technical 

terms used in this report, including the Map Unit 

Properties Table.

Figure 1. Location map of Devils Postpile National Monument. National Park Service map.
DEPO Geologic Resources Inventory Report 1

Introduction

The following section briefly describes the National Park Service Geologic Resources 

Inventory and the regional geologic setting of Devils Postpile National Monument.

Purpose of the Geologic Resources Inventory

The Geologic Resources Inventory (GRI) is one of 12 

inventories funded under the National Park Service 

(NPS) Natural Resource Challenge designed to enhance 

baseline information available to park managers. The 

program carries out the geologic component of the 

inventory effort. The Geologic Resources Division of the 

Natural Resource Program Center administers this 

program. The GRI team relies heavily on partnerships 

with the U.S. Geological Survey, Colorado State 

University, state surveys, and others in developing GRI 

products.

The goal of the GRI is to increase understanding of the 

geologic processes at work in parks and provide sound 

geologic information for use in park decision making. 

Sound park stewardship relies on understanding natural 

resources and their role in the ecosystem. Geology is the 

foundation of park ecosystems. The compilation and use 

of natural resource information by park managers is 

called for in section 204 of the National Parks Omnibus 

Management Act of 1998 and in NPS-75, Natural 

Resources Inventory and Monitoring Guideline. 

To realize this goal, the GRI team is systematically 

conducting a scoping meeting for each of the identified 

270 natural area parks and providing a park-specific 

digital geologic map and geologic report. These products 

support the stewardship of park resources and are 

designed for nongeoscientists. Scoping meetings bring 

together park staff and geologic experts to review 

available geologic maps and discuss specific geologic 

issues, features, and processes. 

The GRI mapping team converts the geologic maps 

identified for park use at the scoping meeting into digital 

geologic data in accordance with their innovative 

Geographic Information Systems (GIS) Data Model. 

These digital data sets bring an exciting interactive 

dimension to traditional paper maps by providing 

geologic data for use in park GIS and facilitating the 

incorporation of geologic considerations into a wide 

range of resource management applications. The newest 

maps come complete with interactive help files. This 

geologic report aids in the use of the map and provides 

park managers with an overview of park geology and 

geologic resource management issues.

For additional information regarding the content of this 

report and current GRI contact information please refer 

to the Geologic Resources Inventory Web site 

(http://www.nature.nps.gov/geology/inventory/).

Regional Location and Geologic Setting

At 323.13 ha (798.46 ac), Devils Postpile is a relatively 

small national monuments in the western United States 

(fig. 1). The monument lies within California’s Sierra 

Nevada, the largest fault-block mountain range in the 

United States (fig. 2). Rising sharply on its eastern side 

from the Great Basin, the Sierra Nevada forms an 

asymmetric mountain range with a western slope that 

descends gradually to near sea level. The mountain range 

is 645 km (400 mi) long, 65 to 130 km (40 to 80 mi) wide, 

and contains eleven peaks that rise to more than 4,270 m 

(14,000 ft) above sea level. 

The monument is located approximately 17 km

(11 miles) southeast of Yosemite National Park near the 

escarpment that defines the eastern edge of the Sierra 

Nevada fault block. The Middle Fork of the San Joaquin 

River flows south through Devils Postpile National 

Monument and then angles west to flow across the Sierra 

Nevada and into the Great Valley of California near 

Fresno. 

Devils Postpile National Monument contains rare 

geologic features—polygonal columns of Quaternary 

basalt, the “posts” for which the monument is named 

(fig. 3). The origin of these great pillars mystified early 

observers, with some surmising that the lava had

“plunged over a precipice, split into prisms, and 

hardened in mid air!” (Huber and Eckhardt 2002). 

In addition to the basalt columns, Quaternary (2.6

million years ago to the present) extrusive volcanic rocks 

and Cretaceous (145.5 to 65.5 million years ago) intrusive 

igneous rocks form the landscape of Devils Postpile 

National Monument (fig. 4). These rocks range in 

composition from granodiorite to leucogranites (granites 

rich in potassium feldspar and aluminum). Rock units

mapped in the vicinity of the Devils Postpile and in 

Yosemite National Park include metamorphosed 

Paleozoic rocks, Jurassic and Triassic volcanic deposits, 

and Jurassic and Triassic sedimentary rocks (Huber and 

Rinehart 1965; Huber 1987). 

Glaciers flowed down the valley of the Middle Fork of 

the San Joaquin River during the Pleistocene and eroded 

most of the lava flows from the area. The glaciers cut a 

vertical face on a remnant of the lava flow that became 

the Devils Postpile, and exposed the interior of the flow 

and the sides of the columns. Today, effects of glaciation

can be seen in the glacial polish and striations on the top 

of the Devils Postpile and in “glacial erratics” (boulders 

deposited some distance from their point of origin)

scattered throughout the monument.
2 NPS Geologic Resources Division

Formation of the Devils Postpile

The 12- to 18-m (40- to 60-ft) high columnar basalt of the 

Devils Postpile ranks as one of the world’s finest 

examples of columnar basalt (fig. 3). About 100,000 years 

ago, a volcano erupted north of Pumice Flat and filled 

the valley of the Middle Fork of the San Joaquin River

with runny basaltic lava. The lava flowed at least 5 km

(3 mi) downstream and accumulated in the vicinity of the 

Devils Postpile to an exceptional depth of approximately

122 m (400 ft) (Huber and Eckhardt 2002). The basaltic 

lava was very fluid and remained molten while it pooled

in the valley behind a natural dam (e.g., a glacial 

moraine). To form columns that are so much longer than 

those formed from a typical basalt flow, the lava behind 

the natural dam had to be remarkably deep. After the 

lava solidified, glacial erosion removed approximately 

half of the flow, leaving the thick center exposed (Allen 

Glazner, University of North Carolina, written 

communication, June 10, 2009).

The top and bottom of the lava cooled and solidified 

rapidly because of exposure to air and cooler granite 

bedrock. As the solidifying lava cooled from the outside 

surfaces inward, it also shrank, as do virtually all liquids 

when frozen or solidified. With shrinkage, tensional 

stresses developed in the lava. The column formation is 

summarized as follows (Huber and Eckhardt 2002):

• Surface cracks developed when the tension 

caused by the shrinkage of cooling was greater 

than the strength of the lava.

• As cracks reached about 25 cm (10 in), they 

branched to form a Y-shape with equal angles 

of approximately 120 degrees around all sides, 

an angle that provides the greatest stress relief.

• Each new crack branched again when it reached 

the critical length, and together with other 

similar cracks formed an irregular polygonal 

pattern. 

To form exceptionally long, uniform, vertical columns, a 

lava flow must be of uniform thickness, be homogeneous 

in chemical composition, and have level top and bottom 

cooling surfaces. Irregularities in chemical composition 

or thickness result in tilted or curved columns. Columns 

exhibiting extreme curvatures formed adjacent to the 

rare vertical columns at Devils Postpile National 

Monument (fig. 3). 

Park History

Although early American Indians camped in and 

frequently visited this region, they left no record of their

observations of the columns of basalt (Kiver and Harris 

1999). Local hermits (e.g., Red Sotcher and Tom Agnew), 

as well as early miners, must also have known about the 

striking columns, but they also left no written records. 

Locally, the area was known as the Devils Woodpile.

When Yosemite National Park was established in 1890, 

its boundaries were more extensive than they are today 

and encompassed the Devils Postpile. Pressure was 

applied immediately by the timber and mining industries

to reduce the park’s boundaries. The first park 

superintendents were military officers, and many of them 

recommended that the southeast part of Yosemite be 

returned to public domain and the resources exploited. 

But in 1895, Captain Alex Rodgers noted that the Devils 

Postpile was justification in itself to maintain park status. 

Although recognition of the importance of the Devils 

Postpile grew, in 1905, Congress removed 1,300 sq km 

(500 sq mi), including Devils Postpile, from Yosemite 

National Park. Newspaper articles about the Devils 

Postpile attracted public attention, while intense mineral 

exploration began in the former parklands. Subsequnt 

decades of mineral exploration determined that the area 

was barren of valuable mineral deposits.

In 1910, Walter Huber, the district engineer for the U.S. 

Forest Service, received an application from a mining 

company to blast the Devils Postpile and use the rock for 

the core of a hydroelectric dam on the Middle Fork of 

the San Joaquin River. Huber, John Muir, and other 

members of the newly formed Sierra Club were opposed 

to this plan. A letter writing campaign to officials in 

Washington led to President William Howard Taft 

designating the area as Devils Postpile National 

Monument on July 6, 1911.
DEPO Geologic Resources Inventory Report 3

Figure 2. The Sierra Nevada fault block. The historic view of the Sierra Nevada shows the great eastern escarpment that rises nearly 3 

km (2 mi) from Owens Valley (foreground). The generalized diagram illustrates the origin of the Sierra Nevada fault block. As tectonic 

forces pulled apart the region (Basin- and- Range extension), the Sierra Nevada was tilted upwards (relative to the Owens Valley block) 

along a basin-bounding normal fault. The “dip” of the beds is the angle the beds make with the surface, while the “strike” represents 

the compass direction that the inclined beds make when they intersect the surface. For an explanation of the various types of faults, 

see figure 17. Both the photograph and diagram are from Matthes (1930). The photograph is also available online from the U.S. 

Geological Survey photographic library at: http://libraryphoto.cr.usgs.gov/htmllib/btch432/btch432j/btch432z/mwc01116.jpg. The 

diagram is available online at: http://www.nps.gov/history/history/online_books/geology/publications/pp/160/sec2a.htm. Both accessed 

November 2009.

EXTENSION

Normal Fault

Dip

Strike
4 NPS Geologic Resources Division

Figure 3. Basalt columns of the Devils Postpile. Uniform composition and thickness resulted in exceptionally long, vertical columns

(about 20 m or 60 ft long). Differences in composition, thickness, cooling rates, and other irregularities produced the curved columns 

to the left of the vertical columns. Column collapse has created a talus pile at the base of the columns. National Park Service 

photograph, available at: http://www.nps.gov/depo/photosmultimedia/photogallery.htm. Accessed November 2009.

Era Period Rock Unit Explanation CENOZOIC Quaternary

Undifferentiated surface 

deposits

Includes pumice, stream deposits, and 

recent organic soils.

Basalt of the Red Cones Unglaciated red cinder cones and lava flows.

Andesite of 

the Devils 

Postpile

Basalt of the Devils Postpile Dark- gray, fine- grained basalt flow. 

Contains abundant feldspar crystals.

Andesite of Mammoth Pass Gray, fine- grained andesite. Minor feldspar 

and pyroxene crystals.

Rhyodacite of Rainbow Falls

Light- gray, fine- grained rhyodacite. 

Exhibits horizontal weathering fractures. 

Some dense, black, columnar-jointed 

outcrops.

Tuff of Reds Meadow

Buff, ash-flow rhyolite. Welded pumice with 

abundant quartz, feldspar, and rock 

fragments.

Andesite of 

the Devils 

Postpile

Basalt of the Buttresses Dark- gray basalt. Abundant olivine crystals 

and pyroxene. Crude columnar jointing.

Regional Unconformity

(time gap of at least 83 million years)

MESOZOIC

Cretaceous

Granite and Granodiorite similar to the 

Cathedral Peak Granite in

Yosemite National Park

Coarse- grained plutonic igneous rock with 

abundant light-colored crystals of quartz 

and feldspar and minor amounts of darkcolored crystals, chiefly biotite. Commonly

contains blocky crystals (phenocrysts) of 

potassium feldspar up to 5 cm (2 in) long. 

Mount Givens Granodiorite

Medium- grained plutonic igneous rock 

composed of quartz, potassium feldspar, 

plagioclase, and the dark-colored minerals, 

biotite and hornblende. 

Figure 4. General stratigraphic column showing rock units exposed in Devils Postpile National Monument and within 1.6 km (1 mi) of 

the monument’s boundaries. Huber and Rinehart (1965) combined the four volcanic units shaded in orange into the “Andesite of the 

Devils Postpile” (Attachment 1). Compiled from Huber and Rinehart (1965) and Clow and Collum (1983). Refer to the Map Unit 

Properties Table for more detailed information.
DEPO Geologic Resources Inventory Report 5

Geologic Issues

The Geologic Resources Division held a Geologic Resources Inventory scoping session for

Devils Postpile National Monument on September 25-26, 2002, to discuss geologic 

resources, address the status of geologic mapping, and assess resource management 

issues and needs. This section synthesizes the scoping results, in particular those issues 

that may require attention from resource managers.

Issues in this section are identified in relative order of 

resource management significance, with the most critical 

discussed first. Potential research projects and topics of 

scientific interest are presented at the end of this section.

The geologic issues section addresses geologic issues as 

they affect the ecosystem, their importance to park 

management, and the extent to which they are 

anthropogenically influenced. At Devils Postpile 

National Monument, the primary geologic issue is the 

potential collapse of the basalt columns. Contact the 

Geologic Resources Division for technical assistance.

Column Collapse

In the 10,000 to 12,000 years since the last glaciers flowed 

down the valley of the Middle Fork, numerous columns 

have fallen from the face of the cliff, creating a talus pile 

of broken columns (fig. 3). Earthquakes and the 

persistent freeze-thaw weathering process in the area 

could topple the vertical columns in Devils Postpile 

National Monument, although the present rate of 

column collapse is sporadic and not well understood.

Earthquakes are likely the principal triggering 

mechanism behind column collapse in the park (Dr. 

Greg Stock, geologist, Yosemite National Park, written 

communication, July 27, 2009). Ground- shaking from

earthquake activity in 1980 may be responsible for the 

collapse of three leaning columns that had been 

separated from nearby vertical columns by as much as 0.3 

m (1 ft) since 1909 (Huber and Eckhardt 2002; Kiver and 

Harris 1999). 

From May 25 to 27, 1980, intense earthquake swarms 

occurred at an epicenter about 3 km (2 mi) southeast of 

Mammoth Lakes, California (fig. 5). Four earthquakes 

with magnitudes of 6.0 or greater on the Richter scale

(along with more than 200 aftershocks of magnitude 3.0 

or greater) shook this eastern Sierra community 

(Archuleta et al. 1982; Harp et al. 1984). These

earthquakes triggered several thousand landslides 

throughout an area of approximately 2,500 sq km (970 sq 

mi), ranging as far west as Yosemite Valley (Harp et al. 

1984). Lesser earthquake swarms accompanied by 

sporadic tremors continued throughout the summer of 

1980, and on July 7, 1980, the three leaning columns fell. 

The earthquake activity in 1980 resulted in the cracking 

of other columns, which currently rest precariously on 

their severed bases. Presumably weakened by small 

earthquakes, columns in the area continue to fall at an 

unpredictable rate. Mammoth Lakes continues to be 

seismically active. For example, from November 3 to 

November 11, 2009, 24 earthquakes with magnitudes 

ranging from 0.1 to 1.5 occurred within a 16-km (10-mi) 

radius of Mammoth Lakes (http://quake.wr.usgs.gov/

recenteqs/FaultMaps/Long_Valley_eqs.htm, accessed 

November 2009). Significant earthquakes that might 

knock down columns also occur along the California—

Nevada border, northeast and southwest of the Devils 

Postpile (fig. 6). 

The prying action of water freezing in the cracks 

between the columns may also trigger column collapse. 

Ice expansion is a slow process, but over time, columns 

may be pried apart, lean, and eventually tumble under 

the pull of gravity. Other processes that might destabilize 

the columns include the prying affect of roots growing in 

fractures and joints and other biological activity.

Preservation of Glacial Features

It is likely that, at one time, nearly all of the upper 

surfaces of exposed rock in Devils Postpile National 

Monument exhibited glacial polish and glacial striations

from the last ice age. Weathering and subsequent erosion 

have removed almost all of the original polished surfaces. 

Only patches of polished surfaces remain, such as those 

on top of the Devils Postpile (fig. 7). Because these 

polished surfaces and striations document the presence 

of glaciers in Devils Postpile National Monument, the 

regulation prohibiting collection of this material is 

especially important. Unsuspecting collectors could 

remove the evidence that glaciers sheared off the top of 

the Devils Postpile, destroying scientific evidence and

also limiting future visitors’ enjoyment and 

understanding of the area (Huber and Eckhardt 2002).

Recurring Volcanism

Several phenomena provide dramatic evidence that 

volcanoes in this region are not extinct: trees dead from 

carbon dioxide gas emanating from the south flank of

Mammoth Mountain near Horseshoe Lake; swarms of 

earthquakes in the 1980s and 1990s; relatively young and 

widespread pumice deposits; and numerous hot springs

such as those at Reds Meadow approximately 0.8 km

(0.5 mi) east of the monument (Huber and Eckhardt 

2002). Active seismicity and ground deformation

suggests that the Long Valley Caldera remains restless. 

The 15- by 30- km (9- by 18- mi) Long Valley Caldera,

formed during an eruption about 760,000 years ago, lies 

northeast of Devils Postpile National Monument (fig. 8).

Mammoth Mountain, a dome complex on the 
6 NPS Geologic Resources Division

southwestern rim of the caldera, erupted approximately 

67,000 years ago (Mahood et al. 2000).

Calderas are cauldron-shaped volcanic features that are 

sometimes confused with volcanic craters. Volcanic 

craters form circular vents from which magma erupts as 

lava, gases, and ejecta. During exceptionally catastrophic 

eruptions, the magma chamber may empty enough so 

that the land above the chamber collapses, forming a 

caldera (e.g., Yellowstone National Park).

Eruptions in the Long Valley Caldera region produce 

both higher-viscosity silicic (felsic) and lower-viscosity 

mafic lavas. Silicic lavas are rich in silica and typically 

form the lighter-colored volcanic rock rhyolite. Darkcolored minerals rich in iron and magnesium compose 

mafic lavas that typically form andesite and basalt, 

darker-colored volcanic rocks. Mafic and silicic lavas 

erupted contemporaneously in four sequences over the 

past 160,000 years (Mahood et al. 2000):

1. the western moat sequence (~160,000 years ago);

2. the Mammoth sequence (~119,000 to 57,000 years 

ago);

3. the northwest caldera sequence (~40,000 to 29,000 

years ago); and 

4. the Inyo chain sequence (~1,400 years ago to the 

present). 

About 550 years ago, a series of explosive magmatic and 

phreatic eruptions and emplacement of lava flows 

occurred at several vents at the Inyo volcanoes (Miller 

1989). Small eruptions occurred about 250 years ago in

Mono Lake at the north end of the Mono-Inyo Craters 

volcanic chain. Magmatic eruptions extrude molten or 

partially molten rock material, while phreatic eruptions 

involve steam, mud, or other material that is not 

incandescent. Phreatic eruptions result from the heating 

and consequent expansion of groundwater due to an 

underlying igneous heat source.

The Long Valley Observatory, one of five U.S. Geological 

Survey Volcano Observatories that monitor volcanoes 

within the United States, monitors and studies geologic 

unrest in and around the Long Valley Caldera—

including earthquakes, ground deformation, and 

degassing activity (http://volcanoes.usgs.gov

/lvostatus.php , accessed November 2009). The most 

likely potential hazard from volcanic activity in the 

Mono Lake—Long Valley area will come from both 

silicic and mafic magma eruptions (Miller 1989). Silicic 

eruptions in the Mono Lake—Long Valley area are 

expected to produce small- to moderate- volume 

pyroclastic eruptions that will form pyroclastic flows,

and small- to moderate- amounts of tephra (volcanic 

material ejected from the vent, such as ash and rock 

fragments). Mafic eruptions will form cinder cones, small 

volumes of tephra, lava flows, and some phreatic 

explosions.

Potential Research Projects

Research projects proposed during the scoping meeting

include:

• Dating lava flows

• Monitoring glacial polish

• Monitoring column stability

• Groundwater chemistry of springs in the 

meadow

• Carbon dioxide flow in the soil, and possible 

tree kill

• Hydrology/geomorphology of the San Joaquin 

River

• Global climate change relative to species 

diversity

• Historic flows of the San Joaquin River

• Possible effects to Devils Postpile National 

Monument springs and watershed from 

proposed groundwater pumping on San 

Joaquin ridge.

The NPS Water Resources Division should be consulted 

with regard to surface water and groundwater projects.
DEPO Geologic Resources Inventory Report 7

Figure 5. Historical earthquake map of California. The yellow star (not to scale) represents the approximate location of Devils Postpile 

National Monument. The arrow points to the location of the 1980 earthquakes near Mammoth Lakes, California. Modified from 

California Geological Survey graphic, available at: http://redirect.conservation.ca.gov/cgs/rghm/quakes/historical/index.htm. Accessed 

November 2009.
8 NPS Geologic Resources Division

Figure 6. Seismicity of California showing earthquakes from 1990 to 2006. The colored circles designate earthquake locations, with the 

various colors indicating depth ranges in kilometers (see depth key above). Note that most of the earthquakes have occurred within 33 

km (21 mi) of the surface. Purple triangles depict cities and purple stars depict state capitols. The yellow star (not to scale) represents 

the approximate location of Devils Postpile National Monument. Modified from U.S. Geological Survey graphic , available at: 

http://earthquake.usgs.gov/regional/states/california/seismicity.php. Accessed November 2009. 

Figure 7. Glacial polish and glacial striations (parallel scratches or lines) on the top of the columns at Devils Postpile National 

Monument. Glacial abrasion caused both features. Due to weathering or illegal collecting, some of the glacial polish has been removed 

from the polygonal tops of the Postpile. Striations provide directional evidence, as well. In this picture, the last glacier followed one of 

two directions, as indicated by the yellow arrow. Modified from a National Park Service photograph by David Scott, available at: 

http://www.nps.gov/depo/photosmultimedia/photogallery.htm. Accessed November 2009.
DEPO Geologic Resources Inventory Report 9

Figure 8. Long Valley Caldera and vicinity. Seismic unrest occurs in the Mono Lake – Long Valley area on a regular basis, and is 

monitored by the Long Valley Observatory. The red star (not to scale) represents the approximate location of Devils Postpile National 

Monument. Modified from U.S. Geological Survey graphic, available at: http://vulcan.wr.usgs.gov/Volcanoes/LongValley/Maps/

map_long_valley.html. Accessed November 2009. 
10 NPS Geologic Resources Division

Figure 9. Exposed ends of the columns at Devils Postpile National Monument showing the polygonal patterns. Note the hexagonal 

shape of the columns. National Park Service photograph, available at: http://www.nps.gov/depo/photosmultimedia/photogallery.htm. 

Accessed November 2009.

Figure 10. A hexagonal pattern is the ideal shape for columnar joints in basalt. If homogenous lava cools uniformly, it shrinks and is 

subject to tensional forces (white arrows) that are equal in all directions. Compared to circles (a) and octagons (b), the hexagon (c) fits 

most efficiently without gaps. The columnar joints at Devils Postpile NM have a large proportion of hexagonal columns, which is rare. 

Not all columns are hexagonal because lava is not completely homogeneous and does not cool perfectly uniformly. As shown in (d), 

some columns are also 5-sided with joints intersecting at nearly 120-degree angles. Graphics and photograph modified from Lillie 

(2005), used with permission.
DEPO Geologic Resources Inventory Report 11

Geologic Features and Processes

This section describes the most prominent and distinctive geologic features and processes 

in Devils Postpile National Monument.

Features exposed in Devils Postpile National Monument 

owe their origin to both fire and ice. Volcanic eruptions, 

igneous intrusions, and mountain-building processes 

tied to the tectonically active margin of western North 

America created the raw material from which Pleistocene 

glaciers carved the park’s distinct landscape. Today, the 

Middle Fork of the San Joaquin River meanders through 

a glacially-carved valley that once supported a river of 

ice. This high-Sierran river corridor sustains healthy 

forests and lush sub-alpine meadows.

Devils Postpile 

The world-renowned columnar jointing at Devils 

Postpile National Monument formed from a lake of lava 

up to 122 m (400 ft) deep and at least 5 km (3 mi) long. A 

single lava flow is rarely this thick. The vertical columns 

of the Devils Postpile represent an extraordinary

occurrence in which uniform cooling conditions in a 

compositionally homogeneous lava produced uniform 

shrinkage. As the lava cooled and shrank, brittle fractures 

started forming that allowed the basalt to crack into long, 

vertical columns. The basalt columns at the Devils 

Postpile have a maximum diameter of 1.1 m (3.5 ft) and

measure up to 18 m (60 ft) long (fig. 3).

The most efficient way to relieve contraction stress is by 

means of three fractures radiating in a Y-shape, 

separated by angles of 120 degrees. The merger of these 

cracks creates hexagonal polygons (figs. 9 and 10). If

conditions were perfect and constant, all such columns 

would be six-sided (Huber and Eckhardt 2002). 

However, regular hexagonal polygons are atypical

because cooling stresses in natural lava flows are never 

completely uniform (Huber and Eckhardt 2002; 

http://geomaps.wr.usgs.gov/parks/depo/dpgeol1.html, 

accessed November 2009). Thus, the columns at Devils 

Postpile are bounded by curved cracks forming 

irregular-shaped polygons with variable numbers of 

sides. In a study of 200 posts, 55% of the columns were 

six-sided, 37% were five-sided, 5% were seven-sided, 

and 2% were four sided (Huber and Eckhardt 2002; 

Kiver and Harris 1999).

With 55% hexagonal polygons, Devils Postpile National 

Monument proves exceptional. By comparison with 

other well-known columnar features, hexagonal 

polygons border 51% of the columns at Giant’s 

Causeway in Northern Ireland, 32.5% of the columns at 

Devils Tower National Monument in Wyoming, and 

16% of the columns at Craters of the Moon National 

Monument in Idaho (Huber and Eckhardt 2002).

Perpendicular columns depend on a relatively horizontal 

ground surface, uniform cooling conditions, and 

homogeneous composition. At the Devils Postpile, 

however, many columns diverge from the vertical. Some 

appear tilted and some display spectacular curved shapes 

(fig. 3). Features and phenomena that may have 

influenced cooling rates and led to curved columnar 

joints include buried hills and valleys, irregular surfaces 

in lava flows, filled lava channels and lava tubes, rain or 

water contacting the lava, and compositional differences 

in the lava.

At Devils Postpile National Monument, the lava columns 

extended many feet in front of the present face after the 

last glacier melted. Sporadic collapse of the columns over 

the years has left a large talus pile of broken posts at the 

base of the current Devils Postpile (fig. 3).

Glacial Features

Numerous episodes of Pleistocene glaciation carved the 

jagged peaks and U-shaped valleys of today’s Sierra 

Nevada (Kiver and Harris 1999). The alpine glacier that 

flowed down the Middle Fork of the San Joaquin River

scoured and scraped away most of the Devils Postpile 

lava flow about 10,000 to 12,000 years ago. The river of 

ice eroded most of the lava flows in the area, but left 

some remnants of the original lava flows. The glacier cut 

a vertical face on the remnant known as the Devils 

Postpile, exposing the interior of the flow and the sides 

of the columns (fig. 3). 

The top of the Devils Postpile reveals not only a cross 

section of the polygonal pattern of the posts, but also the 

polished and scoured effects of flowing ice (fig. 7). As the 

glacier flowed down the valley, fine silt that was 

embedded in the ice acted as nature’s scouring pad and

polished the ends of the columns. Pebbles, boulders, and 

other coarse debris scraped across the columns, 

producing parallel striations and grooves in the basalt.

Rounded bedrock exposures within and near the 

monument that have one steep slope and one gentle 

slope indicate the direction of ice flow. Glaciers flowing 

over fractured bedrock tend to pry and pluck blocks of 

jointed rock away from the downstream side of the 

outcrop. On the upstream side, abrasive material within 

the glacier polishes and smoothes the bedrock surface. 

Plucking action on the downstream side of the rock 

outcrop creates a steep slope while the polishing action 

of ice forms a gentle slope that faces upstream. Such a

glacial feature is called a “roche moutonnée.” Pothole 

Dome on the west side of Tuolumne Meadows in 

Yosemite National Park is an excellent example of a 

roche moutonnée (fig. 11) (Huber 1987). 

Glaciers also carried large boulders (glacial erratics) from 

points upstream and deposited them when the glaciers

melted. Many of the glacial erratics in the Devils Postpile 

area consist of metamorphic rock that only occurs north 

of the monument. Glacial erratics are most abundant on 
12 NPS Geologic Resources Division

the high granite hills and ridges west of the Middle Fork 

of the San Joaquin River

(http://geomaps.wr.usgs.gov/parks/depo/dpgeol1.html, 

accessed November 2009). Yosemite National Park, 

northwest of Devils Postpile, contains many excellent 

geologic features that have resulted from alpine 

glaciation—including horn-shaped peaks, cirque basins, 

moraines, glacial erratics, roche moutonnées, U-shaped 

valleys, glacial polish, and striations.

Other Volcanic Features

The volcanic units in Devils Postpile National 

Monument were originally grouped into a single map 

unit labeled “Andesite of the Devils Postpile” (fig. 4, Map 

Unit Properties Table, and Attachment I). However, 

more recent geologic studies have identified the 

following individual volcanic units within the Devils

Postpile flow: basalt of the Devils Postpile; andesite of

Mammoth Pass; rhyodacite of Rainbow Falls; and basalt 

of the Buttresses (Huber and Eckhardt 2002).

The Mammoth Pass lava, once thought to be the source 

of the Postpile basalt, erupted from a vent near 

Mammoth Pass approximately 67,000 years ago 

(Mahood et al. 2000). Extruded from a higher elevation 

than the Postpile basalt, the Mammoth Pass lava 

cascaded into the Middle Fork valley toward the 

Postpile. But unlike the Postpile basalt, the Mammoth 

Pass lava is andesite, a rock containing more silica than 

basalt and lacking the small but visible crystals of 

feldspar that characterize the Postpile basalt.

Lava erupting from vents just downstream from the 

Devils Postpile solidified into the rhyodacite of Rainbow 

Falls. In comparison to andesite, rhyodacite contains 

more silica and tends to be lighter-colored and finergrained. Perhaps the most striking difference between 

the units is the presence of near-horizontal plate-like 

(“platy”) jointing in the rhyodacite, a feature displayed 

along the road west of Reds Meadow that leads to the 

Rainbow Falls trailhead.

The basalt lava that formed the Buttresses erupted from 

vents west of the monument and flowed eastward into 

the Middle Fork valley. The Buttresses lie southwest of 

the Postpile and form the oldest volcanic unit formerly 

considered part of the Devils Postpile (fig. 4). 

Superficially, the two basalts look alike. However, the 

abundant visible crystals in the Buttress basalt are 

composed of pyroxene, while the visible crystals in the 

Postpile basalt are feldspar. Pyroxenes belong to a group 

of dark-colored minerals that form short stubby crystals. 

Feldspars, on the other hand, form light-colored to 

translucent crystals. 

The tuff of Reds Meadow (fig. 4) represents an entirely 

different type of volcanic rock found near the 

monument. Similar to the aerially extensive Bishop Tuff 

that erupted from the Long Valley Caldera about 760,000 

years ago, the tuff at Reds Meadow resulted from a fiery 

ash cloud released during an explosive volcanic eruption. 

The blistering hot volcanic ejecta fused together to form 

a “welded” tuff. Exposures of this tuff behind the old 

ranger cabin east of Reds Meadow form columnar joints, 

but the columns are nearly horizontal rather than 

vertical.

The only volcanic event younger than the one that 

produced the Postpile flow is the one that built the Red 

Cones, two basalt cinder cones located about 2.4 km

(1.5 mi) southeast of Devils Postpile National 

Monument. The two cones have well-preserved summit 

craters. A basalt flow that issued from the base of the 

southern cone extended down Crater Creek to within

1.6 km (1 mi) of the Middle Fork. Because they are less 

than 10,000 years old, the Red Cones and associated 

basalt flow escaped the powerful excavating force of 

glacial erosion. The eroded pile of cinders near Upper 

Soda Springs Campground may have once looked like 

the Red Cones (Huber and Eckhardt 2002).

Pumice, a frothy volcanic glass, covers the ground at 

various places in the monument area. Pumice is so 

porous and lightweight, it can float in water. The 

unweathered, loosely compacted pumice formed in postglacial time when gas-rich magma of high silica content 

erupted from the Mono and Inyo Craters northeast of 

Devils Postpile National Monument.

Rainbow Falls

Plummeting 31 m (101 ft) over a cliff of volcanic rock, 

Rainbow Falls presents a striking contrast of whitewater 

against black, volcanic cliffs (fig. 12). Located near the 

southern end of the monument about 4 km (2.5 mi) from 

the Ranger Station, Rainbow Falls is the highest waterfall 

on the Middle Fork of the San Joaquin River (fig. 1). On

sunny summer days, rainbows appear in its mist.

Although glaciers polished the surface of the volcanic 

rock and widened the river’s canyon, they did not create 

the present falls. Rather, the key to the falls resides in two 

unequally hard, horizontal rock layers that compose the 

cliff. The eruption that produced the rhyodacite of 

Rainbow Falls occurred in two stages. Lava from the first 

pulse flowed about 1 km (0.6 mi) westward and pooled in 

the Middle Fork of the San Joaquin drainage. The second 

pulse of lava covered the first, allowing the initial flow to 

cool slowly and to fracture into the horizontal, thinly–

spaced joints characteristic of the Rainbow Falls 

rhyodacite (Huber and Eckhardt 2002; http://geomaps.

wr.usgs.gov/parks/depo/dpgeol13.html, accessed 

November 2009). The massive, poorly jointed upper 

layer is more resistant to erosion than the lower platy

layer. 

As water cascades over the cliff, the less resistant rock at 

the base of the falls wears away in a process known as 

“undercutting.” Undercutting erodes the softer rock, 

creating an alcove, or cavern, beneath the massive layer

(fig. 12). As the upper layer loses its support, it eventually 

caves in and breaks into boulders and rock debris at the 

bottom of the falls. 

The falls are also a product of channel migration. 

Following the Pleistocene ice age, the Middle Fork 

flowed about 460 m (1,500 ft) west of its present location
DEPO Geologic Resources Inventory Report 13

(fig. 13). This older channel eroded through the lava 

flows down to granite, leaving a cliff of volcanic rocks for 

its eastern bank. For reasons that are still unclear, the 

Middle Fork’s channel diverted to the east at some point 

upstream from the present falls. The river left its bed to 

follow this new path until it returned to its old channel 

by cascading over the cliff it had cut earlier.

Normally, rivers tend to erode channels to a uniform 

gradient, beveling off and eventually eliminating 

irregularities such as waterfalls. Because of the two 

unequally hard, horizontal rock layers, however,

Rainbow Falls remains a significant irregularity in the 

gradual slope of the Middle Fork’s channel. Due to 

constant undercutting, the cliff has retreated up the 

valley about 152 m (500 ft) from its initial location 

(Huber and Eckhardt 2002).

Mineral Springs

Mineral springs, both hot and cold, occur within or near 

the monument and are associated with recent volcanic 

activity. One cold, highly-carbonated spring flows onto a 

gravel bar on the west side of the Middle Fork in Soda 

Springs Meadow, about 0.2 km (0.1 mi) north of the 

Devils Postpile. The mineral springs and seeps often 

occur where gasses and water vapor escape from hot 

areas deep in the Earth and combine with groundwater 

near the surface. Iron in acidic spring water, oxidized 

upon exposure to the atmosphere, stains the river gravel

orange in the vicinity of Soda Springs (fig. 14). Just east of 

the monument, a hot spring at Reds Meadow further 

attests to the continuing volcanic activity in the area.

San Joaquin River and Soda Springs Meadow

The Middle Fork of the San Joaquin River meanders 

through Soda Springs Meadow (fig. 15). Unlike its 

ancestral counterpart whose channel eroded vertically 

through lava flows, the Middle Fork’s channel erodes 

laterally, from side-to-side across its floodplain. Typical 

of meandering streams, the main current (channel at

maximum depth) migrates from the outside loop of one 

bend to the outside bank of the next bend. Point bars 

develop along the inside bend as the river’s energy 

decreases and sediment is deposited. Opposite the point 

bar, a steep cutbank forms where the main current cuts 

into unconsolidated sediment and soil. Riffles form 

where shallow water flows swiftly over coarser sediment

often located in the straight section of the stream 

between meander loops. Crescent-shaped patterns in the 

meadow, composed of unconsolidated sand and silt, 

mark abandoned river bends (meander scars). The lush 

riparian corridor provides a healthy vibrant habitat for 

plants and animals.

Figure 11. Pothole Dome, a large roche moutonnée in Yosemite National Park. Glaciers shaped Pothole Dome; ice moved from right to left 

over the bedrock surface (arrow). Plucking occurred on the downstream side; grinding and polishing occurred on the upstream side. U.S. 

Geological Survey photograph from Huber (1987), available at: http://pubs.er.usgs.gov/usgspubs/b/b1595. Accessed November 2009. 

Ice Movement
14 NPS Geologic Resources Division

Figure 12. Rainbow Falls, Middle Fork of the San Joaquin River, Devils Postpile National Monument. The water tumbles 31 m (101 ft) over a 

cliff composed of rhyodacite. Undercutting has eroded an alcove to the left of the waterfall. Photograph courtesy Vincent Santucci (NPS 

George Washington Memorial Parkway).

Figure 13. Original channel of the Middle Fork of the San Joaquin River, Devils Postpile National Monument. The dashed, black line depicts 

the original channel that eroded vertically through solidified lava flows. When the Middle Fork flowed back to its original channel from the 

east, it flowed over the previously eroded cliff of rhyodacite, forming Rainbow Falls. Modified from National Park Service map.

Alcove
DEPO Geologic Resources Inventory Report 15

Figure 14. Iron from Soda Springs creates the orange color visible in mid to late summer in Devils Postpile National Monument. National 

Park Service photograph, available at: http://www.nps.gov/depo/photosmultimedia/photogallery.htm. Accessed November 2009. 

Figure 15. The Middle Fork of the San Joaquin River meanders through Soda Springs Meadow, creating geomorphic features such as point 

bars, cut banks, and in-stream riffles. A meander scar defines the pattern of a previous channel. Modified from a National Park Service 

photograph, available at: http://www.nps.gov/depo/photosmultimedia/photogallery.htm. Accessed November 2009.

Point Bar

Cutbank

Riffles

Meander Scar
16 NPS Geologic Resources Division

Map Unit Properties

This section identifies characteristics of map units that appear on the Geologic Resources 

Inventory digital geologic map of Devils Postpile National Monument. The 

accompanying table is highly generalized and is provided for background purposes only. 

Ground-disturbing activities should not be permitted or denied on the basis of 

information in this table.

Geologic maps facilitate an understanding of Earth, its 

processes, and the geologic history responsible for its 

formation. Hence, the geologic map for Devils Postpile 

National Monument provided information for the 

“Geologic Issues,” “Geologic Features and Processes,” 

and “Geologic History” sections of this report. Geologic 

maps are two-dimensional representations of complex 

three-dimensional relationships; their color coding 

illustrates the distribution of rocks and unconsolidated 

deposits. Bold lines that cross or separate the color 

patterns mark structures such as faults and folds. Point 

symbols indicate features such as dipping strata, sample 

localities, mines, wells, and cave openings. 

Incorporation of geologic data into a Geographic 

Information System (GIS) increases the usefulness of 

geologic maps by revealing the spatial relationships 

among geologic features, other natural resources, and 

anthropogenic features. Geologic maps are indicators of 

water resources because they show which rock units are 

potential aquifers and are useful for finding seeps and 

springs. Geologic maps are not soil maps, and do not 

show soil types, but they do show parent material—a key 

factor in soil formation. Furthermore, resource managers 

have used geologic maps to make connections between 

geology and biology; for instance, geologic maps have 

served as tools for locating sensitive, threatened, and 

endangered plant species, which may prefer a particular 

rock unit. 

Although geologic maps do not show where earthquakes 

will occur, the presence of a fault indicates past 

movement and possible future seismic activity. Similarly, 

map units show areas that have been susceptible to 

hazards such as landslides, rockfalls, and volcanic 

eruptions. Geologic maps do not show archaeological or 

cultural resources, but past peoples may have inhabited 

or been influenced by depicted geomorphic features. For 

example, alluvial terraces may have been preferred use 

areas and formerly inhabited alcoves may occur at the 

contact between two rock units.

The geologic units listed in the following table 

correspond to the accompanying digital geologic data. 

Map units are listed in the table from youngest to oldest. 

Please refer to the geologic timescale (fig. 16) for the age 

associated with each time period. The table highlights 

characteristics of map units such as: susceptibility to 

erosion and hazards; the occurrence of paleontological 

resources (fossils), cultural resources, mineral resources, 

and caves or karst; and suitability as habitat or for 

recreational use. Some information on the table are 

conjectural and meant to serve as suggestions for further 

investigation.

The GRI digital geologic maps reproduce essential 

elements of the source maps including the unit 

descriptions, legend, map notes, graphics, and report. 

The following reference is source data for the GRI digital 

geologic data for Devils Postpile National Monument:

Huber, N.K., and C.D. Rinehart. 1965. Geologic map of 

the Devils Postpile quadrangle, Sierra Nevada, 

California. Scale 1:62,500. Geologic Quadrangle GQ437. Reston, VA: U.S. Geological Survey.

The GRI team implements a geology-GIS data model 

that standardizes map deliverables. This data model 

dictates GIS data structure including data layer 

architecture, feature attribution, and data relationships 

within ESRI ArcGIS software, increasing the overall 

quality and utility of the data.

GRI digital geologic map products include data in ESRI 

personal geodatabase, shapefile, and coverage GIS 

formats, layer files with feature symbology, Federal 

Geographic Data Committee (FGDC)-compliant 

metadata, a Windows help file that contains all of the 

ancillary map information and graphics, and an ESRI 

ArcMap map document file that easily displays the map.

GRI digital geologic data are included on the attached 

CD and are available through the NPS Data Store 

(http://science.nature.nps.gov/nrdata/, accessed 

November 2009).
DEPO Geologic Resources Inventory Report 17

Map Unit Properties Table: Devils Postpile National Monument and vicinity 

Colored rows indicate map units within Devils Postpile National Monument.

Age Unit Name

(Symbol) Features and Description Erosion Resistance

Suitability for 

Infrastructure Hazards Paleontological Resources

Cultural 

Resources

Mineral 

Occurrence Habitat Recreation Geologic Significance

QUATERNARY

SURFICIAL DEPOSITS

Alluvium

(Qal)

Valley-fill material. Includes both gravel and finer sediments. Locally contains appreciable 

pumice of non-alluvial origin, especially in the northeast quadrant of the reference map. Flood 

plain deposits in valley lowlands.

Low.

Contains roads 

and 

campgrounds.

Limited 

exposures; none 

documented.

None.

Possible 

American Indian

sites. Limited 

exposure.

Sand and gravel.

Riparian habitat; 

sub-alpine 

meadows. 

Limited aerial 

extent; 

campgrounds.

Stream 

processes.

Talus

(Qt)

Rock debris, largely angular, mapped chiefly at the foot of steep cliffs at higher elevations in the 

Devils Postpile quadrangle. Scattered outcrops of limited aerial extent in the Devils Postpile 

quadrangle. Not exposed in the monument.

High.

Low. Unstable

debris beneath 

cliffs.

Potential 

downslope 

movement.

None.

Minor exposures

outside of the 

monument.

None 

documented on 

reference map.

Bare rock 

exposures. 

Habitat for small 

animals.

Limited aerial 

extent outside 

the monument.

High altitude 

weathering and 

erosion 

processes.

Talus and slopewash

(Qts)

Miscellaneous debris mantling gentle to steep slopes. Locally contains appreciable pumice, 

especially in the northeast quadrant of the reference map. Locally also includes minor glacial 

materials. Not exposed in the monument.

Moderate.

Shuttle bus 

route; Mammoth 

Mountain ski 

lodge.

None 

documented on 

reference map.

None 

documented on 

reference map.

Possible 

American Indian

sites.

Pumice.

Coniferous 

forests and subalpine meadows.

Suitable for most 

uses, including 

hiking, 

picnicking, 

camping, skiing.

High altitude 

weathering and 

erosion 

processes.

Cirque Moraine

(Qm)

Small moraines in cirques, likely of post-Wisconsinan age (the last Pleistocene glacial period, the 

Wisconsinan, began approximately 110,000 years ago and ended approximately 10,000 years ago). 

Scattered high- elevation outcrops of limited aerial extent in the Ritter Range. Not exposed in the 

monument.

Moderate to 

high.

Low. Scattered 

outcrops of 

limited extent. 

Not applicable.

Scattered 

outcrops of 

limited extent. 

Not applicable.

None 

documented on 

reference map.

Remote 

possibility of 

American Indian

sites.

None 

documented on 

reference map.

Alpine tundra 

above tree-line.

Suitable for

backcountry

hiking, pack 

trips, and 

camping.

Features left by 

alpine glaciation.

Glacial Deposits

(Qg)

Chiefly formless glacial till (unstratified, unsorted material) but includes some moraine; largely of 

Wisconsinan age. Not exposed in the monument.

Moderate to 

high.

Contains Inyo 

National Forest 

roads.

Unlikely. 

Gradually 

sloping 

topography. 

None 

documented on 

reference map.

Possible 

American Indian

sites.

None 

documented on 

reference map.

Valley edge 

vegetation. 

Variable altitude.

Suitable for most 

uses, including 

hiking, 

picnicking, 

camping.

Pleistocene 

glacial activity.

VOLCANIC ROCKS

(classification based on and extrapolated from chemical data)

Rhyolite pumice

(Qp)

Light-gray, subangular, rhyolitic pumice fragments and volcanic ash. Mapped in the northeastern 

part of the Devils Postpile quadrangle where it forms a blanket up to several tens of feet in 

thickness in the rather broad, flat area. Elsewhere it is locally a major constituent of units mapped 

as Qal or Qts. Although much of the pumice is of Holocene age (related to Qr domes), much is 

likely older (e.g., related to Qqm). Not exposed in the monument.

Low (ash) to 

moderate (rock 

fragments).

Contains 

unimproved 

Inyo National 

Forest roads.

Relatively flat 

topography 

suggests minimal 

hazards.

None 

documented on 

reference map.

Possible 

American Indian

sites.

Pumice.

Volcanic soils 

and coniferous 

forests.

Mountain biking 

in Deer 

Mountain/Inyo 

Crater Lakes 

area; crosscountry skiing, 

hiking.

Quaternary 

volcanic activity.

Rhyolite of

Mono Craters

(Qr)

Obsidian and other dominantly glassy rocks with varied percentage of quartz; plagioclase, 

sanidine, and biotite phenocrysts. Occurs as a series of domes aligned north-south in the 

northeastern corner of the Devils Postpile quadrangle. Considered to be a southern extension of 

the Mono Craters rhyolitic domes. Not exposed in the monument.

High.

Isolated 

outcrops 

surrounded by 

Qp. Not 

applicable.

Potential 

slumping into 

Deadman Creek.

None 

documented on 

reference map.

Limited 

exposure. 

Possible 

American Indian

sites.

Obsidian, quartz, 

plagioclase, 

sanidine, biotite.

Volcanic soils 

and coniferous 

forests.

Inyo National 

Forest 

recreational 

activities.

Related to Mono 

Craters volcanic 

eruptions

Basalt of the

Red Cones

(Qbr)

Occurs as cinders in the Red Cones and as a flow extending from the base of the southernmost 

cone. Typically scoriaceous with prominent phenocrysts of plagioclase and olivine. Exposed on

the southeastern slope of the Middle Fork of the San Joaquin River, southeast of the monument.

High.

Hiking trails. 

Inyo National 

Forest.

Unstable slopes. None.

Possible 

American Indian

sites.

Phenocrysts of 

plagioclase and 

olivine.

Surrounded by 

coniferous 

forest.

Inyo National 

Forest 

recreational 

activities.

Erupted less 

than 10,000 years 

ago. Escaped 

glacial erosion.

Olivine-bearing

Quartz Latite

(Qoq)

Flow of dark-gray rock with aphanitic to glassy matrix and abundant plagioclase and sanidine 

phenocrysts. Minor exposure of limited aerial extent in the northeastern corner of the Devils 

Postpile quadrangle. Not exposed in the monument.

High.

Outcrop of 

limited extent. 

Not applicable.

Relatively gentle 

topography. None.

Limited 

exposure.

Possible 

American Indian

sites.

Phenocrysts of 

plagioclase and 

sanidine.

Outcrop of 

limited extent. 

Not applicable.

Outcrop of 

limited extent. 

Not applicable.

Quaternary 

volcanic activity.

Andesite

(Qa)

Includes scattered flow remnants of porphyritic andesite (phenocrysts of plagioclase and olivine) 

and andesitic cinder in cones north and east of Mammoth Mountain. All are not necessarily from

the same source, but of approximately the same age. Not exposed in the monument.

Moderate 

(cinder) to high 

(flow).

Scattered, minor 

outcrops. 

Insignificant.

Scattered, minor 

outcrops. 

Insignificant.

None.

Scattered, minor 

outcrops. 

Insignificant.

Phenocrysts of 

plagioclase and 

olivine.

Scattered, minor 

outcrops. 

Insignificant.

Scattered, minor 

outcrops. 

Insignificant.

Quaternary 

volcanic activity.

Andesite of

Pumice Butte

(Qap)

Cinder cones and associated flows. Typically scoriaceous; nonporphyritic. Contacts only 

approximate; partly distinguished from older andesite in the area by aerial photo interpretation. 

Includes dacite that forms two knobs in the northwest part of the outcrop area, which may be 

older than the andesite. Exposed at Pumice Butte, southeast of the monument. 

High.

Limited to area 

around Pumice 

Butte, Inyo 

National Forest.

Potential rockfall 

on steep slopes

in backcountry.

None.

Possible 

American Indian

sites.

None. Coniferous 

forest.

Intersects John 

Muir Trail.

Quaternary 

volcanic activity.
Colored rows indicate map units within Devils Postpile National Monument.

DEPO Geologic Resources Inventory Report 18

Age Unit Name

(Symbol) Features and Description Erosion Resistance

Suitability for 

Infrastructure Hazards Paleontological Resources

Cultural 

Resources

Mineral 

Occurrence Habitat Recreation Geologic Significance

Quartz Latite of

Mammoth Mountain

(Qqm)

Light-gray, nearly black in glassier phases. Dominantly glassy texture with varied percentage of 

plagioclase and biotite phenocrysts. Commonly flow- banded. Previously designated as 

Pliocene(?). Associated with Mammoth Mountain, east of the monument. Not exposed in the 

monument.

High.

Mammoth 

Mountain ski 

area – highest in 

California.

Outgassing of 

carbon dioxide 

(south flank of 

Mammoth 

Mountain).

None.

Possible 

American Indian

sites and 

remnants of early 

mining activity.

Phenocrysts of 

plagioclase and 

biotite.

Bare rock 

exposures and 

conifers in Inyo

National Forest.

Skiing, mountain 

biking, hiking, 

and camping.

Mammoth 

Mountain is a 

volcanic dome 

complex on the 

southwestern 

rim of Long 

Valley Caldera. 

Andesite of the

Devils Postpile

(Qad)

Light- to dark-gray, commonly porphyritic with phenocrysts of plagioclase and olivine; rarely 

vesicular. Platy and columnar jointing well developed locally. Forms columnar basalt and talus at 

the Devils Postpile. Forms cliff at Rainbow Falls (rhyodacite of Rainbow Falls).

Unfractured 

welded tuff is

high; fractured, 

platy tuff is less 

resistant.

Suitable for 

roads and trails.

Contains Reds 

Meadow Resort, 

east of 

monument.

Potential rockfall 

from column 

collapse.

None.

Possible 

American Indian

sites (campfires 

and trails); 

remnants of early 

mining.

Phenocrysts of 

plagioclase and 

olivine.

Monument lies 

within lush highSierran river 

corridor; 

coniferous 

forest.

Postpile viewing,

Rainbow Falls 

Trail, King Creek 

Trail, John Muir 

Trail.

World renowned

columnar 

jointing and 

glacial features 

(polish, 

striations).

Rhyolitic Tuff of

Reds Meadow

(Qtr)

Crystal-vitric tuff with phenocrysts of quartz and sanidine in nearly equal amounts. Welded in 

part, with two distinct zones of dense welding, indicating a compound flow unit. Banded 

(eutaxitic) structure prominent in welded portions. Base consists of unconsolidated pumice, ash, 

and exotic fragments. Scattered, isolated outcrops with limited aerial extent. Not exposed in the 

monument.

High.

Outcrops too 

minor to be 

significant.

Potential seismic 

activity. None.

Limited 

exposures; 

possible 

American Indian

sites.

Phenocrysts of 

quartz and 

sanadine.

Scattered, minor 

outcrops in 

forest. 

Insignificant.

Fishing, hiking,

and pack horse 

trails (nearby 

resort).

Hot springs 

attest to ongoing 

volcanic activity.

QUATERNARY/

TERTIARY

(Pliocene or 

Pleistocene)

Andesite

(QTa)

Medium-gray aphanitic rock, locally containing plagioclase and pyroxene phenocrysts; exposed 

only in the extreme northeastern corner of the Devils Postpile quadrangle. Not exposed in the 

monument.

High.

Outcrops too 

minor to be 

significant.

Outcrops too 

minor to be 

significant.

None.

Check adjoining 

Mt. Morrison 

quadrangle.

Phenocrysts of 

plagioclase and 

pyroxene.

Outcrops too 

minor to be 

significant.

Recreation tied 

to activities 

common to the 

surrounding 

national forest.

Pliocene–

Pleistocene 

volcanic activity.

Regional Unconformity Between Quaternary Rocks and Tertiary Rocks

TERTIARY

(Pliocene)

Quartz Latite of

Two Teats

(Tqt)

Light-gray to dark- or purplish-gray, glassy to microcrystalline rock with abundant plagioclase 

and lesser biotite and amphibole phenocrysts. Flow structures common. Locally fragmental. 

Mapped in the northeastern part of the Devils Postpile quadrangle. Not exposed in the 

monument.

High.

Semi-linear 

outcrops in Inyo 

National Forest.

Potential rockfall 

in backcountry. None.

Limited 

exposures; 

possible 

American Indian

sites.

Phenocrysts of 

plagioclase, 

biotite, 

amphiboles.

Alpine and 

subalpine 

vegetation.

Backcountry

hiking and 

camping.

Pliocene 

volcanic activity.

Andesite of

Deadman Pass

(Tad)

Series of interbedded andesitic flows, cinders, and rubble. Flow rock commonly vesicular; mostly

non-porphyritic. Includes scattered remnants of andesitic rock not necessarily from the same 

source, but of approximately the same age. Exposed in a linear outcrop trend striking northwest 

from Deadman Pass, north of the monument. Not exposed in the monument.

High. Backcountry

trails.

Potential rockfall 

in backcountry. None.

Possible 

American Indian

sites (campfires 

and trails).

None 

documented on 

reference map.

Coniferous 

forest.

Hiking, 

packhorse trails, 

and fishing at 

Clark Lakes.

Pliocene 

volcanic activity.

Regional Unconformity Separating Tertiary Rocks from Cretaceous Rocks

CRETACEOUS

GRANITIC ROCKS

Rocks similar to

Cathedral Peak Granite

(Kcp)

Rocks similar to the Cathedral Peak Granite. Composition from granodiorite to leucogranite with 

average composition of mafic quartz monzonite (26% quartz; 27% K-feldspar; 41% plagioclase; 

6% mafics, chiefly biotite). Generally coarse-grained and commonly porphyritic with blocky 

phenocrysts of K-feldspar up to 5 cm (2 in) long. K-Ar determinations on biotite yield ages of 

about 85 million years. Leucogranite limited to Fish Creek-Silver Divide area. Kcp intrudes Kmg. 

Forms its highest peaks in Devils Postpile National Monument on either side of the Buttresses.

High.

Suitable for 

trails. Exposed in 

both the 

monument and 

Inyo National

Forest.

Potential rockfall 

along the 

Buttresses.

None.

Possible 

American Indian

sites (campfires 

and trails); 

remnants of early 

mining.

Phenocrysts of 

plagioclase and 

biotite.

Sub-alpine 

meadows and 

coniferous 

forests.

Rainbow Falls 

Trail, King Creek 

Trail; John Muir 

Trail.

One of many 

plutons 

emplaced in the 

Mesozoic that 

core the Sierra 

Nevada.

Mount Givens

Granodiorite

(Kmg)

Medium-grained. Composition from granodiorite to quartz monzonite with average composition 

of felsic granodiorite (24% quartz; 18% K-feldspar; 43% plagioclase; 15% mafics, chiefly biotite 

and hornblende). Likely continuous with Mount Givens Granodiorite to south of the map area. 

K-Ar determinations on biotite and hornblende south of the Devils Postpile quadrangle yield ages 

of about 85 million years. Not exposed in the monument.

High.

Suitable for 

trails. Exposed in 

Inyo National

Forest.

Potential rockfall 

in backcountry. None.

Possible 

American Indian

sites (campfires 

and trails); 

remnants of early 

mining.

Quartz; Kfeldspar; 

plagioclase; 

mafics, chiefly 

biotite and 

hornblende.

Sub-alpine 

meadows and 

coniferous 

forests.

Backcountry use 

including hiking, 

camping, and 

pack trips.

Cretaceous 

plutonic 

intrusion.

Granodiorite of

Kuna Crest

(Kk)

Rock dominantly granodiorite but of variable composition and texture. In the Rush Creek area, 

contains zones of numerous mafic inclusions and stringers of mafic mineral segregation. Named 

for exposures on Kuna Crest, Mono Craters quadrangle. Exposed in the northwestern part of the 

Devils Postpile quadrangle. Floors Garnet and Thousand Island Lakes. Not exposed in the 

monument.

High.

Suitable for trails 

in backcountry 

of Inyo National

Forest.

Forms gentle 

slopes along lake 

shores.

None.

Possible 

American Indian 

sites (campfires 

and trails).

None 

documented on 

reference map.

Coniferous 

forests.

Backcountry use 

including hiking, 

camping, and 

pack trips.

Cretaceous 

plutonic 

intrusion.
Colored rows indicate map units within Devils Postpile National Monument.

DEPO Geologic Resources Inventory Report 19

Age Unit Name

(Symbol) Features and Description Erosion Resistance

Suitability for 

Infrastructure Hazards Paleontological Resources

Cultural 

Resources

Mineral 

Occurrence Habitat Recreation Geologic Significance

Wheeler Crest

Quartz Monzonite

(Kwc)

Medium- grained, commonly porphyritic with phenocrysts of K-feldspar 1 cm (0.4 in) long on 

average. Biotite and hornblende are the chief mafic minerals. Correlated with Wheeler Crest 

Quartz Monzonite to the southeast. K-Ar determinations on hornblende in the Mount Tom 

quadrangle to the southeast yield ages of about 100 million years. Limited to isolated outcrops in 

the northeastern corner of the reference map. Not exposed in the monument.

High.

Low. Isolated 

pods of rock on 

slopes above 

Deadman Creek

and Glass Creek.

Potential rockfall

in backcountry. None.

Possible 

American Indian 

sites (campfires 

and trails).

Phenocrysts of 

K-feldspar.

Coniferous 

forests.

Backcountry 

trails might cross 

this unit.

Cretaceous 

plutonic 

intrusion.

CRETACEOUS and JURASSIC

Quartz Monzonite of 

Shellenbarger Lake

(KJs)

Fine- to medium- grained, commonly porphyritic with micrographic groundmass and 2 to 5 mm 

(0.08 to 0.2 in) albite phenocrysts of possible replacement origin. Exposed west of the monument, 

but not exposed in the monument.

High.

Backcountry 

exposures in 

Inyo National 

Forest.

Potential rockfall 

in backcountry. None.

Possible 

American Indian 

sites.

Phenocrysts of 

albite (feldspar).

Subalpine 

meadows and 

coniferous 

forests.

Backcountry use.

Cretaceous or 

Jurassic plutonic 

intrusion.

Felsic dikes and masses

(KJfd)

Fine-grained, rhyolitic, commonly with flow banding. Most dikes occur as a swarm in and near 

the granodiorite near KJf and are somewhat generalized on the map. Not exposed in the 

monument.

High. Linear features. 

Not applicable.

Linear features. 

Not applicable. None. Linear featuresof limited extent.

None

documented on 

reference map.

Linear features. 

Not applicable.

Linear features. 

Not applicable.

Dikes intrude 

older rocks.

Mafic dikes and masses

(KJmd)

Fine- to medium- grained, occasionally porphyritic or amygdaloidal. Mapped as a dike and two 

small masses south of Iron Mountain (southwest of the monument). These small exposures

contain magnetite-rich hornblendite. Not exposed in the monument.

High.

Linear feature 

and two small

masses. Not 

applicable.

Linear feature 

and two small 

masses. Not 

applicable.

None.

Linear feature 

and two small 

masses. Not 

applicable.

Magnetite.

Linear feature 

and two small 

masses. Not 

applicable.

Linear feature 

and two small 

masses. Not 

applicable.

Dikes intrude 

older rocks.

Diorite and Gabbro

(KJd)

Fine- to coarse-grained. Occurs as scattered masses not necessarily of the same age. Gabbro is 

limited chiefly to the central part of mass south of Iron Creek, and masses north of Stevenson 

Meadow, south of Island Pass, and northeast of Davis Lakes. Isolated exposures near Trinity 

Lakes, along Kings Creek, and southeast of Pumice Butte. Not exposed in the monument.

High.

Limited 

exposure in 

vicinity of the 

monument.

None. Not 

exposed in the 

monument.

None.

Limited 

exposure in 

vicinity of the 

monument. 

None 

documented on 

reference map.

Sub-alpine 

meadows.

Limited 

exposure.

Cretaceous or 

Jurassic plutonic 

intrusion.

Granodiorite of

King and Fish Creeks

(KJf)

Fine- to coarse-grained. Varied composition and texture with average composition of 

granodiorite. Both King Creek and Fish Creek masses contain numerous metavolcanic inclusions, 

including large masses of part to nearly completely assimilated material. Numerous mafic and 

rhyolitic dikes cut King Creek rocks. KJf intruded by Kcp and Kmg. Mapped south and west of 

the monument. Not exposed in the monument.

High.

Low. 

Backcountry 

exposure in Inyo 

National Forest. 

Suitable for 

trails.

Potential 

backcountry 

rockfall.

None.

Possible 

American Indian 

sites (campfires 

and trails);

remnants of early 

mining (?).

None 

documented on 

reference map.

Sub-alpine lakes 

and coniferous 

forests.

Hiking and pack 

horse trails;

camping.

Cretaceous or 

Jurassic plutonic 

intrusion.

Granodiorite of

Jackass Lakes

(KJj)

Medium- grained, equigranular. Exposed only in a small area at western edge of the quadrangle 

and named for more extensive exposures in the Merced Peak quadrangle. Not exposed in the 

monument.

High.

Exposure is too 

minor to be 

applicable.

Exposure is too 

minor to be 

applicable.

None.

Exposure is too 

minor to be 

applicable.

None 

documented on 

reference map.

Limited outcrops 

in Inyo National 

Forest.

Exposure is too 

minor to be 

applicable.

Cretaceous or 

Jurassic plutonic 

intrusion.

JURASSIC

Quartz Monzonite of

Lee Vining Canyon

(Jl)

Medium- grained with varied texture. Contains dense fine- grained felsic rock, commonly 

porphyritic, locally banded, possibly younger. Numerous dikes and sills, not shown, are likely

related to this unit. Cuts the metamorphic rocks exposed in the San Joaquin Mountain ridge. 

Correlated with quartz monzonite exposed in Lee Vining Canyon and elsewhere in the Mono 

Craters quadrangle. Rb-Sr whole-rock age determinations from this unit in the Mono Craters 

quadrangle yielded an age of about 190 million years. Limited to the northeastern part of the 

Devils Postpile quadrangle at Carson Peak and north of Deadman Pass. Not exposed in the 

monument.

High.

Low. 

Backcountry 

exposures in 

Inyo National

Forest.

Potential 

backcountry 

rockfall in 

vicinity of 

Carson Peak.

None.

Possible 

American Indian 

sites (campfires 

and trails); 

remnants of early 

mining (?)

None 

documented on 

reference map.

Sub-alpine 

meadows and 

coniferous 

forests.

Backcountry use. Jurassic plutonic 

intrusion.

Granodiorite of

Rush Creek

(Jr)

Medium- grained, ranging in composition from granodiorite to diorite. Generally exhibits a 

pronounced linear structure and less pronounced foliation. Minor exposure along the northern 

border of the map continues into Mono Craters quadrangle. Not exposed in the monument.

High.

Exposure is too 

minor to be 

applicable.

Exposure is too 

minor to be 

applicable.

None.

Exposure is too 

minor to be 

applicable.

None 

documented on 

reference map.

Exposure is too 

minor to be 

applicable.

Exposure is too 

minor to be 

applicable.

Jurassic plutonic 

intrusion.

METAMORPHIC ROCKS

(prefix “meta” omitted from rock names for convenience)

Metavolcanic Rocks Near Twin Island Lakes

(approximately 300 m [1,000 ft] thick.

Basalt

(Jb)

Medium dark- gray to dark- gray, thick flows, massive, finely porphyritic with labradorite laths 

ranging from a fraction of a millimeter to 5 mm (0.2 in) in length, set in a dense matrix of 

plagioclase, biotite, chlorite, and hornblende. Minor exposure along the northwestern border of 

the Devils Postpile quadrangle. Not exposed in the monument.

High.

Exposures are

too minor to be 

applicable.

Exposures are

too minor to be 

applicable.

None.

Exposures are 

too minor to be 

applicable.

Plagioclase

phenocrysts

(labradorite).

Exposures are 

too minor to be 

applicable.

Exposures are 

too minor to be 

applicable.

Metamorphosed 

volcanic rocks.

Andesite and Basalt

(Ja)

Medium dark-gray to dark-gray. Lenticular sequence of thin to thick flows, commonly 

interlayered with thinly laminated to thin-bedded tuffaceous rocks; typically porphyritic with 

tabular phenocrysts of plagioclase (andesine to labradorite) as large as 2 cm (0.8 in) in maximum 

dimension. Locally contains quartz amygdules. Resembles Jab and JTRa. Minor exposure along 

the northwestern border of the quadrangle, west of Twin Island Lakes. Not exposed in the 

monument.

High.

Exposures are 

too minor to be 

applicable.

Exposures are 

too minor to be 

applicable.

None.

Exposures are 

too minor to be 

applicable.

Plagioclase

phenocrysts

(andesine to 

labradorite).

Exposures are 

too minor to be 

applicable.

Exposures are 

too minor to be 

applicable.

Metamorphosed 

volcanic rocks.
Colored rows indicate map units within Devils Postpile National Monument.

DEPO Geologic Resources Inventory Report 20

Age Unit Name

(Symbol) Features and Description Erosion Resistance

Suitability for 

Infrastructure Hazards Paleontological Resources

Cultural 

Resources

Mineral 

Occurrence Habitat Recreation Geologic Significance

Sedimentary Rocks

(Js)

A generally well-bedded sequence of sedimentary rocks, tuffaceous in part, in the northwestern 

part of the quadrangle. Composed chiefly of siltstone and fine-grained sandstone but includes 

tremolite-bearing carbonaceous marble, pelitic hornfels and slate (both typically carbonaceous)

and granule conglomerate. Locally includes several feet of graded, rhythmically bedded siltstone

in layers ranging from 1 mm to 3 cm (0.04 to 1.2 in). Not exposed in the monument.

High.

Exposures are 

too minor to be 

applicable.

Exposures are 

too minor to be 

applicable.

None.

Exposures are 

too minor to be 

applicable.

Tremolite.

Exposures are 

too minor to be 

applicable.

Exposures are 

too minor to be 

applicable.

May contain 

potential 

evidence of 

Jurassic 

depositional 

environments.

Metavolcanic Rocks of the Ritter Range

(approximately 4,600 m [15,000 ft] thick)

Undifferentiated

volcanic rocks,

chiefly Breccia

(Jbr)

Undifferentiated volcanic rocks, chiefly breccia. Highly varied unit that includes nearly all 

lithologic types of metavolcanic rocks found in the metavolcanic sequence but consists chiefly of 

tuff breccia, somewhat lesser amounts of crystal tuff and crystal-lithic tuff, hypabyssal intrusives, 

and bedded tuff. Composition ranges from rhyolite to basalt but averages near dacite or 

rhyodacite. Rocks are typically structureless, at most, weakly foliated; primary texture generally 

dominates. Lithic fragments range in maximum dimension from a few mm to more than 0.3 m

(1 ft); fragments are typically volcanic, but locally are sedimentary or granitoid. Overprinted 

pattern indicates an area of extensive migmatization south of Bench Canyon at the western edge 

of the quadrangle. Exposed west of the monument.

High.

Trails. 

Backcountry 

exposures in 

Inyo National 

Forest.

Potential 

backcountry 

rockfall 

associated with 

steeper slopes.

None.

Possible 

American Indian 

sites (campfires 

and trails); 

remnants of early 

mining (?).

None 

documented on 

reference map.

Alpine tundra 

above tree-line, 

sub-alpine 

meadows, and 

coniferous 

forests.

Trails for 

backcountry use.

Metamorphosed 

volcanic rocks.

Andesite and Basalt

(Jab)

Medium dark- gray to dark- gray. Thin to thick flows locally interlayered with bedded tuffaceous 

rocks. Fine-grained to conspicuously porphyritic, containing tabular plagioclase (oligoclase to 

labradorite) phenocrysts a few mm to as much as 3 cm (1.2 in) in maximum dimension. In several 

places the unit is a breccia with irregular-shaped fragments of coarsely porphyritic rock in a finegrained matrix. Porphyritic phases bear a striking resemblance to Ja and JTRa. Fragments of Jab

are found in overlying volcanic breccia. Not exposed in the monument.

High.

Low. Minor, 

scattered 

outcrops in 

backcountry of 

Ritter Range.

Minor, scattered 

outcrops in 

Ritter Range 

pose few, if any, 

hazards.

None.

Potential cultural 

sites are more 

likely to be found

in adjacent units.

Plagioclase 

phenocrysts

(oligoclase to 

labradorite).

Coniferous 

forests.

Minor, scattered 

outcrops are 

insignificant with 

regards to 

recreational use.

Metamorphosed 

volcanic rocks.

JURASSIC and TRIASSIC

Metavolcanic Rocks of Shadow Creek and Mammoth Crest

(approximately 4,900 m [16,000 ft] thick)

Undifferentiated

volcanic rocks

(JTRu)

Highly varied unit that contains nearly all the rock types of the entire metavolcanic sequence, but 

consists chiefly of crystal-lithic tuff. Composed of discontinuous, lenticular, dominantly 

pyroclastic units; rhyolitic to basaltic in composition, but average near dacite or rhyodacite. Rock 

types (in order of decreasing abundance) are: crystal-lithic tuff; tuff breccia; tuffaceous sandstone 

and siltstone; flows and hypabyssal intrusives, mostly mafic. Fragments of underlying formations 

occur locally at or near the base. Rocks in the stratigraphic interval between the base and roughly 

the easternmost crystal tuff (JTRx) unit are characteristically more schistose than most other 

rocks in the metavolcanic sequence, and primary structures are sparse. Elsewhere in the 

sequence, generally well preserved primary textures and structures exist south of Garnet Lake; 

from Garnet Lake north, preservation becomes progressively poorer with accompanying increase 

in dominance of metamorphic fabric. Hornfelses, schists, and gneisses predominate in the Rush 

creek area, and are included with JTRu although the high degree of metamorphic recrystallization 

and associated anomalous structural trends makes their equivalence uncertain and the location of 

the contact with undifferentiated volcanic rocks, chiefly breccia (Jbr) tentative. Based on 

lithologic similarities, rocks in the Mammoth Crest area are likely equivalent to those in the 

stratigraphic interval between Agnew Meadows and Shadow Lake. Exposed northwest of the 

monument. Not exposed in the monument.

High.

Trails. 

Backcountry 

exposures in 

Inyo National 

Forest.

Potential 

backcountry 

rockfall 

associated with 

steeper slopes.

Early Jurassic 

pectinoid 

(scallop-like) 

pelecypod 

bivavles

recovered from 

calcareous 

sandstones and 

siltstones (JTRc) 

near Garnet Lake 

and north of 

Thousand Island 

Lake in same 

stratigraphic 

interval as JTRu.

Possible 

American Indian 

sites (campfires 

and trails); 

remnants of early 

mining (Minaret 

Mine).

Lead was mined 

at the abandoned 

Minaret Mine 

(claim turned 

over to U.S.

Forest Service in 

1990s).

Sub-alpine 

meadows and 

coniferous 

forests.

Trails for 

backcountry use, 

including trail to 

abandoned 

Minaret Mine.

Metamorphosed 

volcanic rocks.

Andesite and Basalt

(JTRa)

Medium dark- gray to dark- gray. Thin to thick flows and hypabyssal intrusive. Aphanitic to 

porphyritic with plagioclase (albite to andesine) phenocrysts as much as 3 cm (1.2 in) long; locally 

with quartz amygdules up to 1 cm (0.4 in) in maximum dimension. Coarsely porphyritic phases 

bear striking megascopic resemblance to Jab. Locally extensively replaced by epidote, particularly 

on Volcanic Ridge, northwest of the monument. Not exposed in the monument.

High.

Trails. Exposed 

in the 

backcountry of 

the Inyo 

National Forest.

Potential 

backcountry 

rockfall 

associated with 

steeper slopes.

None.

Possible 

American Indian 

sites (campfires 

and trails); 

remnants of early 

mining (?)

Plagioclase 

phenocrysts 

(albite to 

andesine); 

epidote.

Sub-alpine 

meadows and 

coniferous 

forests.

Trails for 

backcountry use.

Metamorphosed 

volcanic rocks.

Crystal Tuff

(JTRx)

Light- to medium- gray. Lithic fragments are common but sparse; typically massive or weakly 

foliated parallel to regional strike. Rhyolitic to quartz latitic in composition. White and pink 

feldspar is distinguishable in outcrops as small wispy dark patches, bent around crystals or lithic 

fragments, giving the rock an aspect reminiscent of the banded (eutaxitic) structure of welded 

tuff; most of these layers likely originated as ash flows. Exposed in northwest-southeast trending 

outcrops northwest of the monument.

High.

Trails. Exposed 

in the 

backcountry of 

the Inyo 

National Forest.

Potential 

backcountry 

rockfall 

associated with 

steeper slopes.

None.

Possible 

American Indian 

sites (campfires 

and trails); 

remnants of early 

mining (?)

White and pink 

feldspar.

Sub-alpine 

meadows and 

coniferous 

forests.

Crossed by John 

Muir Trail. 

Backcountry use.

Metamorphosed 

volcanic rocks.

Dacite and Andesite

(JTRd)

Medium- to dark- gray, massive porphyritic flows and hypabyssal intrusive rocks, locally 

amygdaloidal with quartz or calcite fillings; grades into breccia in a few places. Original texture is 

generally well preserved. Includes a coarsely porphyritic, medium- gray, quartz latitic flow or 

hypabyssal intrusive, locally amygdaloidal, west of Weber Lake. Exposed in narrow northwestsoutheast trending outcrops. Not exposed in the monument.

High.

Low. Narrow, 

linear outcrops 

in the backcountry of Inyo 

National Forest.

Narrow outcrop 

bands make 

potential hazards 

insignificant.

None.

Potential cultural 

sites are more 

likely to be found

in adjacent units.

Quartz.

Exposures are 

too minor to be 

applicable.

Exposures are 

too minor to be 

applicable.

Metamorphosed 

volcanic rocks.
Colored rows indicate map units within Devils Postpile National Monument.

DEPO Geologic Resources Inventory Report 21

Age Unit Name

(Symbol) Features and Description Erosion Resistance

Suitability for 

Infrastructure Hazards Paleontological Resources

Cultural 

Resources

Mineral 

Occurrence Habitat Recreation Geologic Significance

Calcareous 

Sedimentary

Rocks

(JTRc)

Typically thin-bedded tuffaceous sandstone and siltstone, commonly calcareous. Minor amounts 

of marble, slate, and conglomerate. Gross sedimentary features are preserved, but microscopic 

granoblastic fabric; well foliated in places. Sporadic occurrences of garnet, pyroxene, tremolite 

and/or actinolite, and plagioclase. Rocks composing the thin, sedimentary lens near Minaret 

Summit contain a much smaller proportion of volcanic material than most sedimentary rocks in 

the metavolcanic sequence. Exposed in narrow northwest-southeast trending outcrops 

northwest of the monument.

High.

Low. Narrow, 

linear outcrops 

in the

backcountry of 

the Inyo 

National Forest.

Narrow outcrop 

bands make 

potential hazards 

insignificant.

Early Jurassic 

pectinoid 

(scallop-like) 

pelecypod

bivalves found 

north of Garnet 

Lake and north 

of Thousand 

Island Lake; 

ammonites

(indeterminate) 

found south of 

Minaret Mine.

Potential cultural 

sites are more 

likely to be found

in adjacent units.

Garnet, 

pyroxene, 

tremolite and/or

actinolite, and 

plagioclase.

Exposures are 

too minor to be 

applicable.

Exposures are 

too minor to be 

applicable.

Metamorphosed 

sedimentary 

rocks.

Sandstone, Siltstone,

and Slate

(JTRss)

North of Thousand Island Lake: Medium- to dark- gray siltstone and slate. Locally, slate contains 

andalusite and garnet. Aphanitic to fine-grained, thinly laminated or massive; locally contains thin 

laminations composed of quartz, plagioclase and amphibole; primary texture is generally well 

preserved but locally phyllitic. 

North of Davis Lakes

Variable. Silstone 

less resistant

than slate and 

sandstone.

: Dark- gray to medium light- gray siltstone and fine- to medium-grained 

tuffaceous sandstone; thinly laminated to thin-bedded; beds locally graded. Exposed in narrow 

outcrops in the northwestern corner of the Devils Lake quadrangle. Not exposed in the 

monument.

Exposures are 

too minor to be 

applicable.

Exposures are 

too minor to be 

applicable.

None.

Potential cultural 

sites are more 

likely to be found

in adjacent units.

Andalusite and 

garnet found in 

slate.

Exposures are 

too minor to be

applicable.

Exposures are 

too minor to be 

applicable.

Metamorphosed 

sedimentary 

rocks.

Metavolcanic Rocks of Silver Creek

Undifferentiated

Volcanic Rocks

(JTRv)

Dominantly intermediate composition so extensively recrystallized that the primary textures and 

structures are obscure or absent and correlation with units exposed in the Ritter Range Pendant is 

uncertain. Rocks bearing some similarities to JTRx were tentatively recognized in a few outcrops. 

Well-developed foliation is the dominant structure with schist and gneiss the most common rock. 

Crystal-lithic tuff was likely the chief parent rock type; a few mafic flows and calcareous epiclastic 

rocks formed a quantitatively minor part of the sequence. Exposed in the southern part of the 

Devils Postpile quadrangle. Not exposed in the monument.

High.

Low. Exposed in 

the backcountry 

of Inyo National

Forest.

Potential 

backcountry 

rockfall 

associated with 

steeper slopes.

None.

Possible 

American Indian 

sites (campfires 

and trails).

None 

documented on 

reference map.

Sub-alpine 

meadows and 

coniferous 

forests. Silver 

Creek drainage.

Backcountry use.

Metamorphism 

has destroyed 

primary textures 

and structure.

Regional Unconformity Separating Mesozoic Rocks from Paleozoic Rocks

PENNSYLVANIAN and PERMIAN

Metasedimentary Rocks

(approximately 1,500 m [5,000 ft] thick)

Younger Metasedimentary Rocks

(younger sedimentary sequence lithologically similar to and correlated with Pennsylvanian and Permian [?] rocks of Mount Morrison Pendant 

southeast of reference map; some silicate marble and calc-hornfels present in eastern part of sedimentary belt near Spooky Meadow

lithologically similar to older sedimentary rocks, but structurally concordant, and thus included herein, with younger sedimentary rocks)

PIPh

Dark, moderately well-bedded siliceous hornfels and small amounts of interbedded pelitic 

hornfels, slate, and quartzite; several large irregular areas of massive light-colored cherty or 

silicified rock northeast of Agnew Meadows. Minor interlayering with metavolcanic rocks at the 

top of the unit may possibly be primary, but appears more likely to be of tectonic origin. Parent 

rocks were chiefly shale and siltstone. Exposed in the northeastern corner of the Devils Postpile 

quadrangle. Not exposed in the monument.

High.

Low. Exposed in 

the backcountry 

of Inyo National

Forest.

Potential 

backcountry 

rockfall 

associated with 

steeper slopes.

None.

Possible 

American Indian 

sites (campfires 

and trails).

None 

documented on 

reference map.

Coniferous 

forests. Backcountry use.

Metamorphosed 

Paleozoic 

sedimentary 

rocks.

PIPm

Marble in two small outcrops north of Minaret Summit is lithologically similar to the Mount 

Baldwin Marble in the Mount Morrison quadrangle. Medium- gray to medium dark- gray; thinly 

laminated to massive; crinoidal in part; clean; typically too sheared and deformed to determine a 

regional trend. The two outcrops are separated by a massive tuffaceous conglomerate containing 

many marble fragments. Not exposed in the monument.

High.

Only two minor 

exposures. 

Insignificant.

Only two minor 

exposures. 

Insignificant.

Crinoids.

Only two minor 

exposures. 

Insignificant.

None 

documented on 

reference map.

Only two minor 

exposures. 

Insignificant.

Only two minor 

exposures. 

Insignificant.

Metamorphosed 

Paleozoic 

sedimentary 

rocks.
Colored rows indicate map units within Devils Postpile National Monument.

DEPO Geologic Resources Inventory Report 22

Age Unit Name

(Symbol) Features and Description Erosion Resistance

Suitability for 

Infrastructure Hazards Paleontological Resources

Cultural 

Resources

Mineral 

Occurrence Habitat Recreation Geologic Significance

SILURIAN and ORDOVICIAN

Older Metasedimentary Rocks

(rocks highly deformed, and regional trend in bedding appears closer to north than trend in younger sedimentary rocks; 

rocks included in this unit are lithologically similar to, and thus herein correlated with, pre-Pennsylvanian rocks to southeast in Mount Morrison Pendant)

SOh

Dark- colored, chiefly bedded to massive pelitic and siliceous hornfels; locally abundant thin to 

thick beds of silicated marble and thin beds of calc-hornfels, both containing plagioclase, 

tremolite, diopside, and wollastonite as common minerals; minor amounts of fine- to mediumgrained quartzite. Parent rocks were shale, siltstone, marly siltstone, and quartz-bearing 

limestone. Exposed in the northeastern corner of the Devils Postpile quadrangle.

High.

Low. Scattered 

outcrops in the 

backcountry of 

the Inyo 

National Forest.

Minor rockfall 

potential in 

backcountry.

None.

Possible 

American Indian 

sites (campfires 

and trails).

Plagioclase, 

tremolite, 

diopside, and 

wollastonite.

Coniferous 

forests.

Suitable for most 

uses, including 

hiking, 

picnicking, and 

camping.

Metamorphosed 

Paleozoic 

sedimentary 

rocks.

SOm Silicated marble in beds generally poorly layered or massive. Exposed as isolated outcrop pods 

within SOh. Not exposed in the monument. High. Low. Isolated pods within SOh.

Exposures are 

too minor to be 

applicable.

None.

Exposures are 

too minor to be 

applicable.

None 

documented on 

reference map.

Exposures are 

too minor to be 

applicable.

Exposures are 

too minor to be 

applicable.

Metamorphosed 

Paleozoic 

sedimentary 

rocks.

Reference: Huber, N.K., and C.D. Rinehart. 1965. Geologic map of the Devils Postpile quadrangle, Sierra Nevada, California. Scale 1:62,500. Geologic Quadrangle GQ-437. Reston, VA: U.S. Geological Survey.
DEPO Geologic Resources Inventory Report 23

Geologic History

This section describes the rocks and unconsolidated deposits that appear on the digital 

geologic map of Devils Postpile National Monument, the environment in which those 

units were deposited, and the timing of geologic events that created the present 

landscape.

Using radiometric dates, relative dating techniques, and 

geological observations from California, Oregon, and 

Nevada, geologists have pieced together the complex 

geologic history of the Sierra Nevada region and the 

western margin of North America (fig. 16). Some of the 

geologic history can be interpreted in considerable 

detail, whereas other sections of the geologic record are 

less complete because data are not available.

For roughly 500 million years, the western margin of 

North America has been an active tectonic margin that 

has experienced a broad spectrum of deformation. 

Sedimentary rock units have been folded and faulted and 

displaced from their original site of deposition (fig. 17).

Magma bodies have cooled at great depths or erupted 

violently at the surface. These igneous intrusions 

(batholiths, pluton, and stocks) and extrusive, volcanic 

rocks are now exposed along the crest of the Sierra 

Nevada. Episodes of tectonic compression dislodged and 

transported enormous masses of rock from west to east. 

In contrast, east-west extensional forces have pulled the 

region apart. Vast tracks of California coast have 

wrenched free from the rest of the continent and 

continue to slide northward. The world renowned 

columnar basalt columns in Devils Postpile National 

Monument record a significant, but relatively young,

chapter in this remarkable and exceptionally dynamic 

geologic history.

Paleozoic Era (542 to 251 million years ago)

Latest Proterozoic (2,500 to 542 million years ago) and 

Cambrian (542 to 488.3 million years ago) rocks in the 

western United States comprise three vertically stacked 

stratigraphic units: 1) a Late Proterozoic diamictite 

(poorly sorted sedimentary rock) and volcanic 

succession; 2) a latest Proterozoic and Lower Cambrian 

succession of terrigenous detritus; and 3) an uppermost 

Lower Cambrian through Upper Cambrian marine 

carbonate and shale sequence (Stewart 1991).

Approximately 500 million years ago, most of what is 

now California lay submerged to the west of the 

emerging North American continent (fig. 18). The 

western margin of North America was a passive margin—

like today’s East Coast—with the continent and its 

adjacent ocean basin traveling on the same lithospheric 

plate. 

Interpretation of the Cambrian through Silurian geologic 

history of the Sierra Nevada presents a challenge because 

subsequent mountain-building episodes, emplacement 

of Sierra Nevada batholiths, and other tectonic events 

have deformed and displaced these Early Paleozoic rock 

units. From the Late Devonian (385.3 to 359.2 million 

years ago) through the Early Mississippian (359.2 to 

345.3 million years ago), the passive western margin 

along the California coast transformed into an active 

subduction zone with oceanic crust being subducted 

beneath the North American plate in the initial phase of 

the Antler Orogeny (fig. 16) (Dickinson 1977; Poole and 

Sandberg 1977; Johnson et al. 1991). This oceaniccontinental crust collision generated the Roberts 

Mountains Thrust, a thrust fault that displaced Cambrian 

through Devonian strata from west to east. Mountains 

emerged in central Nevada, and marine waters spread 

over a large portion of the continent (fig. 19).

The Roberts Mountains Thrust and subsequent 

Paleozoic tectonic episodes are known as orogenic 

“continent-accretion phases” wherein rocks were added 

to the western margin of the craton. Mississippian 

through Permian strata in the southwestern United 

States document a series of tectonic episodes that were 

both local and regional in scale and included uplift, 

tilting, folding, erosion, basin segmentation, and 

subsidence (Trexler et al. 1991). 

During the Pennsylvanian, thrust faults associated with 

oceanic-continental convergence along the western 

margin accreted oceanic deposits to the mainland. These 

marine sediments were dominated by dark chert, deepmarine mud, igneous rocks, dark shale, siltstone, isolated 

carbonate plateaus and atolls, and locally thick basinal 

and slope-margin clastic sediments (Ross 1991). South 

America began closing with North America, and the 

forces of this continent-continent collision were felt far 

inland, generating the northwest-southeast trending 

Ancestral Rocky Mountains. 

Several basins that would eventually become prolific oiland gas- producing basins formed in the late Paleozoic

including the Delaware, Midland, and Paradox basins

(fig. 20). The Sonoma Orogeny, a Late Permian-Triassic 

tectonic episode, further accreted marine sediments onto 

the continental margin as the major land masses 

continued to suture together to form the supercontinent, 

Pangaea (Trexler et al. 1991; Dubiel 1994; Dunston et al. 

2001).

Mesozoic Era (251 to 65.5 million years ago)

Triassic-Jurassic Periods (251 to 145.5 million years ago)

Extension (plates pulling apart) and strike-slip (plates 

sliding past each other) faulting of the crust during the 

Early Triassic truncated the continental margin of 

California and formed a north-trending continental 

margin that paralleled the foothills of the current Sierra 
24 NPS Geologic Resources Division

Nevada. This north-trending margin became the locus of 

eastward subduction beneath North America in the Late 

Triassic (Schweickert 1978; Oldow et al. 1989; Saleeby et 

al. 1992; Stevens 1991). 

The Late Permian—Early Triassic Sonoma Orogeny 

compressed, shortened, and deformed the sequence of 

rocks now exposed in the Ritter Range, west and north 

of Devils Postpile National Monument (Schweickert 

1978; Oldow et al. 1989). Accreted Paleozoic and 

Mesozoic sedimentary and volcanic rocks in the Ritter 

Range record evidence of long vanished seaways and 

island volcanoes that existed west of the present-day 

Sierra Nevada. An 11 km (7 mi) thick sequence of ashflow tuffs, lava flows, bedded pyroclastic rocks, and 

marine limestones document latest Permian to midJurassic deposition across a low-lying terrain periodically 

inundated by rising sea level (Fiske and Tobisch 1978). 

Plate subduction along the active western margin of 

North America continued throughout the Mesozoic. As 

the oceanic plate subducted beneath the overriding 

North American continent, magma was generated at 

depth and belts of volcanoes formed atop the overriding 

plate, parallel to the subduction zone in a manner similar 

to today’s Mount St. Helens and other volcanoes in the 

Cascade Range (fig. 21A). 

Significant magma was generated beneath the Cordillera 

in the Middle Jurassic, and volcanic islands formed an 

unknown distance west or southwest of the west coast of 

North America (Huber and Rinehart 1965; Hamilton 

1978; Schweickert 1978; Oldow et al. 1989). During the 

Late Jurassic, these Middle Jurassic volcanic islands 

accreted to the North American continent.

Major tectonic plate reorganization occurred during the 

Late Jurassic. The Gulf of Mexico opened and the North 

American lithospheric plate rotated counterclockwise. 

To accommodate this plate motion, a large transform 

fault zone (or “megashear”), referred to as the MojaveSonora megashear, developed at a fairly high angle to the 

west coast (relatively parallel to what is now the MexicoUnited States border) and truncated the southwestern 

margin of North America. This northwest-southeast 

trending megashear zone resulted in approximately 800 

to 1,000 km (500 to 600 mi) of left-lateral, strike-slip

displacement (Kluth 1983; Stevens et al. 2005; Anderson 

and Silver 2005; Haenggi and Muehlberger 2005). 

Cretaceous Period (145.5 to 65.5 million years ago)

Continued subduction along the west coast of North 

America initiated the Sevier Orogeny about 105 million 

years ago in the latest Jurassic. The orogeny continued 

through the Cretaceous and into the Paleogene (fig. 16). 

The north-south trending Sevier fold-and-thrust belt 

extends from Canada through western Montana, eastern 

Idaho, southwestern Wyoming, central Utah, and into 

southeastern Nevada (Lageson and Schmitt 1994). 

During the Early Cretaceous, the orogeny transported

regional-scale Proterozoic and Paleozoic megathrust 

sheets of rock from west to east (DeCelles 2004). Later in 

the Cretaceous, the orogeny shortened the crust along 

weak bedding planes in relatively shallow Paleozoic and 

Mesozoic sedimentary rock, producing “thin-skinned” 

thrust faults that generally get younger to the east. In 

contrast, the Late Cretaceous to Eocene Laramide 

Orogeny produced “basement-cored” reverse faults that 

often took advantage of preexisting faults that formed 

during the Late Precambrian (Gries 1983; Erslev 1993; 

DeCelles 2004). 

Sevier thrusting resulted in a greatly thickened crust in 

the region that would become the Basin- and- Range 

physiographic province. The thickened crust played an 

important role in the later pull-apart (tensional) forces 

that produced the present Sierra Nevada, the Basin- andRange province, and episodes of Cenozoic volcanism 

(Livaccari 1991; Kiver and Harris 1999).

Emplacement of continental-margin plutons from 

Mexico to the Alaskan peninsula and volcanic activity

above the associated subduction zone reached maximum 

development in the Cretaceous (Oldow et al. 1989; 

Christiansen et al. 1994; Dubiel 1994; Lawton 1994; 

Peterson 1994). Rocks and sediment caught in the 

subduction zone were bent, broken, and 

metamorphosed as they were compressed against and 

under the North American plate. 

As the oceanic plate descended into the asthenosphere 

and mantle part of the lithosphere, rocks melted and 

magma was generated that had the composition of basalt 

or andesite, dark-colored rocks low in silica. The magma 

rose through the silica-rich continental crust, partially 

melting the overriding lithosphere, and becoming more 

granitic. About 140 to 80 million years ago, the granitic 

magma that would become the Sierra Nevada batholith 

pooled at depths of only 3 to 8 km (1.8 to 4.9 mi) beneath 

the active volcanoes at the surface (Fiske and Tobisch 

1978; Hamilton 1978; Huber 1987; Oldow et al. 1989; 

Kiver and Harris 1999). 

The Sierra Nevada batholiths (including those now 

exposed within Yosemite National Park), a composite 

mass about 100 km (40 mi) wide, consists of hundreds of 

distinct plutons that range in area up to 1,000 sq km (380 

sq mi) (Hamilton 1978). Volcanic deposits on the crest of 

the Sierra Nevada and Ritter Range are the extrusive 

equivalents of their adjacent plutons. Intense volcanic 

activity produced extraordinary amounts of volcanic 

material. For example, a 4-km (2.5-mi)- thick section of 

ash-flow tuff in the Ritter Range contains a lens of 

caldera-collapse breccia more than 1-km (0.6-mi)- thick, 

suggesting the sequence records the remains of a midCretaceous caldera fill complex (Fiske and Tobisch 

1978).

As Sevier orogenic thrust packages thickened the crust 

along the western margin of North America, the Western 

Interior Basin, the region east of the fold-and-thrust belt, 

subsided. At a time when mountains rose along the 

western margin, rifting between North and South 

America opened the Gulf of Mexico, and seawater 

spread northward into the Western Interior Basin, which 

would soon become the Western Interior Seaway. 
DEPO Geologic Resources Inventory Report 25

Marine water also began to transgress southward onto 

the continent from the Arctic region. 

The seas advanced and retreated many times during the 

Cretaceous until the most extensive interior seaway ever 

recorded drowned much of western North America. The 

elongate Western Interior Seaway extended from today’s 

Gulf of Mexico to the Arctic Ocean, a distance of about 

4,800 km (3,000 mi) (fig. 22). 

The Cretaceous seaway was the last marine incursion 

into the interior of North America. The seaway receded 

from the continental interior with the onset of the 

Laramide Orogeny (about 70 to 35 million years ago). 

This orogeny marked a pronounced eastward shift in 

tectonic activity as the angle of the subducting slab of 

oceanic crust flattened and compressive forces were felt 

throughout northern Arizona and Utah and into 

Colorado (fig. 21B). Unlike Sevier thrust faults, Laramide 

thrust faults displaced deeply-buried Precambrian 

plutonic and metamorphic rocks that are now exposed in 

the core of the Rocky Mountains. Sevier thrust faults dip 

at a low angle (generally 10° to 15°) relative to Earth’s 

surface. In contrast, Laramide thrust faults have steeplydipping fault planes at the surface that curve and flatten 

in Precambrian crystalline rocks at depths to 9 km (5.7 mi 

[30,000 ft]) below sea level (Gries 1983; Erslev 1993).

Once the magmatic source for the ancestral Sierra 

Nevada was eliminated, erosion became the dominant 

force shaping the range. By the end of the Cretaceous, 

most of the older volcanic and metamorphic rocks had 

been eroded, exposing the granite core of the ancestral 

Sierra (Huber 1987; Huber and Eckhardt 2002).

Elevations of the mountain summits were low compared 

to the present-day Sierra Nevada, and did not inhibit the 

westward flow of streams and rivers draining the interior 

of the continent. 

Cenozoic Era (65.5 million years ago to the present)

Paleogene and Neogene (“Tertiary”) Period (65.5 to

2.6 million years ago)

The Devils Postpile region contains exposures of 

Tertiary andesite and quartz latite, a light- gray to darkor purplish- gray volcanic rock with abundant 

plagioclase and lesser biotite and amphibole 

phenocrysts; however, no Tertiary exposures are found 

in the monument (Huber and Rinehart 1965). 

Until approximately 70 million years ago, nearly the 

entire western North American margin was in 

compression, causing thrusting and margin-parallel 

transcurrent faulting. In central California, west and 

south of the Sierra plutonic belt, the proto-San Andreas 

fault formed in the Late Cretaceous to Paleocene. 

Oblique subduction of the Farallon plate beneath North 

America resulted in approximately 1,500 km (930 mi) of 

northward displacement of the Salinian Terrane, a 

wedge-shaped crustal block of west-central California,

along the proto-San Andreas fault. The Salinian Terrane 

is bounded by the San Andreas fault on the east, the 

Pacific Ocean on the west, and is exposed from Point 

Arena south to Point Sur (Oldow et al. 1989). 

Widespread magmatism occurred along the continental 

margin during the late Oligocene and early Miocene. By 

the early Miocene (23 to 16 million years ago), the 

divergent plate boundary (spreading ridge) that 

separated the Pacific plate from the Farallon plate

intersected the western margin of the North American 

plate (fig. 23). The collision of the divergent boundary 

with the active margin terminated subduction along this 

segment of the coast and activated the San Andreas 

strike-slip fault. As one of California’s most outstanding 

geologic features, the San Andreas fault is more than 

1,000 km (620 mi) long, with a cumulative right-lateral 

displacement of greater than 320 km (200 mi) (Oldow et 

al. 1989).

The coastal region was segmented into individual basins. 

Crustal extension and strike-slip faulting (transtension), 

accompanied by oblique shortening and strike-slip 

(transpression), generated extensive folding and thrust 

faulting (Oldow et al. 1989).

The change from subduction to strike-slip movement 

further removed support for the thick crust in the Great 

Basin. The crust collapsed under the Great Basin, 

widening the Basin- and -Range Province. Crustal 

thinning produced tensional (pull-apart) faults in the 

eastern Sierra Nevada and Basin-and-Range and the 

subsequent rise of hot mantle material. The resulting 

thermal expansion and partial melting of the mantle 

reduced rock density, and account for the unusually high 

elevation of the eastern Sierra (Huber 1987; Park et al. 

1996). 

Considerable debate and research continues with regard 

to when the Sierra Nevada developed as a mountain 

range. One view, based on the isotopic composition of 

authigenic minerals (typically clay minerals that have not 

been transported from the spot where they formed), 

suggests that the Sierra Nevada existed as a major 

topographic feature throughout much of the Cenozoic

(Chamberlain and Poage 2000; Chamberlain et al. 2002; 

Chamberlain et al. 2005; Mulch et al. 2005; Mulch et al. 

2006; Cassel et al. 2009). In this view, most of the 

topography was established in the early Tertiary with 

little change in elevation occurring over the past 16 

million years.

A contrary opinion, based on river incision rates and 

cosmogenic dating of cave sediments, suggests that a late 

Cenozoic uplift gave rise to the present elevation of the 

Sierra Nevada (Stock et al. 2004; Stock et al. 2005). In this 

view, rapid river incision of approximately 0.2 mm/yr

(0.008 in/yr) from 2.7 to 1.5 million years ago supports a 

tectonically driven, late Pliocene to Quaternary uplift.

Until about 3 million years ago, the main fork of the San 

Joaquin River may have had its headwaters as far east as 

Nevada (Huber and Eckhardt 2002). The river crossed 

what is today the Sierran crest north of Minaret Summit. 

Highly resistant rocks in the Ritter Range diverted the 

southwestward flow of the San Joaquin River to the 
26 NPS Geologic Resources Division

southeast and then south through the Devils Postpile 

area. South of the Devils Postpile, the river changed its 

course to the southwest, flowing across the less resistant 

granite at the south end of the Ritter Range. 

About 3 million years ago, lava flows filled the river 

channel north of Minaret Summit. These lava flows are 

exposed today as the reddish-colored, layered rocks 

visible on the slope above the road descending to Agnew 

Meadows (Huber and Eckhardt 2002). The lava flow and 

the growth of the east-facing Sierra Nevada escarpment 

isolated the present San Joaquin drainage basin and 

blocked any renewal of a trans-Sierra San Joaquin River. 

Quaternary Period (2.6 million years ago to present)

Quaternary rocks and sediments unconformably overlie 

Cretaceous granite and granodiorite in Devils Postpile 

National Monument (fig. 4). During the Pleistocene 

Epoch (2.6 million to 11,700 years ago), heavy snowpacks

in the Sierra Nevada fed glaciers that descended through

stream-cut canyons, deepening and widening them. Ice

accumulated on the east slope of the Ritter Range, 

forming glaciers that flowed down the Middle Fork of 

the San Joaquin River, shaping today’s U-shaped valley. 

Fractures in the rock helped the glaciers erode and shape 

the bedrock. The glaciers carved cirques and sculpted

the jagged peaks in the neighboring Ritter Range and 

Minarets.

Volcanic activity coincided with Sierran alpine 

glaciation. Deposition of the tuff near Reds Meadow 

occurred concurrent with the volcanic activity that 

created the Long Valley Caldera about 760,000 years ago. 

River erosion removed much of the tuff from the central 

part of the valley and exposed the basalt at the 

Buttresses. The rhyodacite lava of Rainbow Falls erupted 

from vents downstream from the present site of the 

Devils Postpile. About 67,000 years ago, andesite lava 

erupted near Mammoth Pass and flowed into the Middle 

Fork valley.

The basaltic lava responsible for the Devils Postpile 

erupted less than 100,000 years ago, forming a lake of 

lava that covered several square kilometers of the valley

floor. Stream and glacial erosion removed much of the 

accumulated volcanic rock from the Middle Fork valley 

and exposed a vertical section of the Devils Postpile. The 

last glaciation, which ended approximately 12,000 years 

ago, polished the tops of the famous columns and 

marked the rocks with glacial striations and grooves. 

Less than 10,000 years ago, after the last glacier melted 

from the valley, the Red Cones and their associated lava 

flow formed. Airfall pumice deposits along the trails and 

hillsides fell on the area during the past few hundred 

years, likely from an eruption from one of the plug 

domes located along the Mono Craters fissure just east of 

the Sierra Nevada.

The Mono Craters and Inyo domes between Mono Lake 

and Mammoth Lakes have been erupting episodically 

during the past few thousand years. The most recent 

domes were formed about 600 years ago. The results of 

glacial activity and recent erosion processes are visible in 

the dramatic landscape of Yosemite National Park. The 

Geologic Story of Yosemite National Park (Huber 1987) 

contains a detailed description of the effect of these 

erosion processes on the landscape at Yosemite, and on 

the Sierra Nevada in general.
DEPO Geologic Resources Inventory Report 27

Figure 16. Geologic time scale. Included are major life history and tectonic events occurring on the North American continent. Red lines 

indicate major unconformities between eras. Radiometric ages shown are in millions of years (Ma). Compass directions in parentheses 

indicate the regional location of individual geologic events. Adapted from the U.S. Geological Survey, http://pubs.usgs.gov/fs/2007/3015/

with additional information from the International Commission on Stratigraphy. http://www.stratigraphy.org/view.php?id=25. Accessed 

November 2009.
28 NPS Geologic Resources Division

A) Normal Fault

B) Reverse (thrust) Fault

C) Strike-slip Fault

Figure 17. Diagrams of general fault types. A) In a “normal” fault (top diagram), rocks in the “hanging wall” above the fault plane move 

downward relative to rocks in the “footwall” below the fault plane. These terms developed as a result of early mining geology. Walking down 

a fault plane in a mine, miners walked on the “foot” wall, while the rocks that hung above their heads were in the “hanging” wall. 

Extensional forces commonly generate normal faults. B) In a “reverse” fault (middle diagram), the hanging wall has moved up relative to the 

footwall. The only difference between a “reverse” fault and a “thrust” fault lies in the angle of the fault plane from the surface of the Earth. If 

the angle is more than about 15%, the fault is a “reverse” fault. In reverse or thrust faults, compressive forces juxtapose older (underlying), 

hanging wall strata against younger, footwall strata. Typically, compressive forces fold the strata prior to breaking along the fault plane. C) 

In “strike-slip” faulting, the rocks on each side of the fault slide laterally past each other. In this case, the slip is “right-lateral” because 

features (e.g., the fence) on one side of the fault have moved to the right relative to the other side of the fault (as viewed across the fault). 

Strike-slip faulting usually contains elements of normal faulting and reverse faulting, as well. U.S. Geological Survey graphics, available at:

http://geomaps.wr.usgs.gov/parks/deform/gfaults.html. Accessed November 2009.

EXTENSION

COMPRESSION
DEPO Geologic Resources Inventory Report 29

Figure 18. Late Cambrian paleogeographic map of North America. Approximately 500 million years ago, the Sierra Nevada region and future 

site of Devils Postpile National Monument (yellow star) lay offshore of the “passive” western margin of the emerging North America 

continent. The brown color indicates exposed land, light blue represents shallow marine, and dark blue shows deep marine. Map modified 

from the Late Cambrian map of Dr. Ron Blakey (Northern Arizona University), available online at: http://jan.ucc.nau.edu/rcb7/namC500.jpg. 

Accessed November 2009.

500 Million Years Ago

Equator
30 NPS Geologic Resources Division

Figure 19. Early Mississippian paleogeographic map of southwestern North America. Approximately 340 million years ago, the western 

margin of North America was an “active” tectonic margin with a slab of oceanic lithosphere being subducted beneath the North American 

continent. The Antler Orogeny (mountain-building episode) caused mountains to emerge in central Nevada and Idaho and a major 

transgression to spread marine environments across western North America. The black line (dashed where uncertain) represents the 

general location of subduction zones and active margins that bordered western and southeastern North America in the Devonian and 

Mississippian. The yellow star represents the approximate location of today’s Devils Postpile National Monument. The brown color denotes

land, light blue represents shallow marine, and dark blue represents deeper marine environments. The general direction of movement of 

both plates is indicated by the white arrows. Modified from Dr. Ron Blakey (Northern Arizona University), available online at: 

http://jan.ucc.nau.edu/rcb7/garm340.jpg. Accessed November 2009.

North American Plate

Oceanic Plate

340 Million Years Ago
DEPO Geologic Resources Inventory Report 31

Figure 20. Late Permian paleogeographic map of southwestern North America. About 255 million years ago, the Sonoma Orogeny accreted 

marine sediments to the western margin of North America. South America (SA) continued to close the proto-Gulf of Mexico and collide with 

North America. Forces associated with this collision formed the northwest-southeast trending Ancestral Rocky Mountains. By the Late 

Permian, many of the basins that began forming in the Late Mississippian and Pennsylvanian had filled with sediment, but the Delaware 

Basin (DeB) and Midland Basin (MiB), prolific oil- and gas- producing basins, continued to subside. By the Triassic, all of the major 

landmasses had come together to form the supercontinent, Pangaea. The yellow star represents the approximate location of today’s Devils 

Postpile National Monument. The black line marks the general trend of the subduction zone between the North American lithospheric plate 

and the oceanic plate. The dashed red line represents a very approximate location between South America and North America. The brown 

and yellowish-brown colors denote land, light blue represents shallow marine, and dark blue represents deeper marine environments. 

Modified from Dr. Ron Blakey (Northern Arizona University), available online at: http://jan.ucc.nau.edu/rcb7/garm255.jpg. Accessed 

November 2009.

North American Plate

Oceanic Plate

SA

Ancestral Rocky Mountains

255 Million Years Ago
32 NPS Geologic Resources Division

A) Oceanic-continental convergence (Andean-style, or Cascadian-style, subduction).

B) “Flat slab”-style subduction that gave rise to the Laramide Orogeny and the Rocky Mountains.

Figure 21. Schematic drawings of subduction zones off the western margin of the United States during the Mesozoic. A) In the Early 

Triassic, the angle of subduction was relatively steep as the oceanic plate converged with the North American continent. This type of 

subduction is seen today along the western margin of North and South America. B) In the Cretaceous, the subduction zone flattened out in a 

style known as “flat slab” subduction. Compressive forces and melting were felt much farther inland than normal, giving rise to the Rocky 

Mountains. Schematics are from the U.S. Geological Survey, available online at: http://geomaps.wr.usgs.gov/parks/province/rockymtn.html. 

Accessed November 2009.
DEPO Geologic Resources Inventory Report 33

Figure 22. Late Cretaceous paleogeographic map of North America. About 85 million years ago, the Sevier Orogeny, caused by subduction 

of the Kula and Farallon plates beneath the North American plate, deformed the western margin into a linear chain of mountains. The 

Western Interior Seaway (WIS) connected the Arctic Ocean with the widening Gulf of Mexico. The yellow star represents the approximate 

location of today’s Devils Postpile National Monument. The thick black line marks the approximate location of the subduction zone. The red 

line is the approximate location of the spreading center separating the Farallon and Kula plates. The brown color denotes land, light blue 

represents shallow marine, and dark blue represents deeper marine environments. Modified from Dr. Ron Blakey’s (Northern Arizona 

University) paleogeographic map, available online at: http://jan.ucc.nau.edu/rcb7/namK85.jpg. Accessed November 2009. Western Interior Seaway

85 Million Years Ago
34 NPS Geologic Resources Division

Figure 23. Growth of the San Andreas Fault System. When the spreading center between the Pacific plate and Farallon plate intersected the 

North American plate, a transform fault formed (San Andreas Fault zone), causing strike-slip (transpressional) movement. The Farallon plate 

has been subdivided into the Juan de Fuca plate, to the north, and the Cocos plate, to the south. Modified by Jason Kenworthy (NPS 

Geologic Resources Division) from Dr. Ron Blakey’s (Northern Arizona University) paleogeographic maps: 

http://jan.ucc.nau.edu/~rcb7/nam.html, accessed January 2010.
DEPO Geologic Resources Inventory Report 35

Glossary

This glossary contains brief definitions of technical geologic terms used in this report. Not all 

geologic terms used are referenced. For more detailed definitions or to find terms not listed 

here please visit: http://geomaps.wr.usgs.gov/parks/misc/glossarya.html. Definitions are 

based on those in the American Geological Institute Glossary of Geology (fifth edition; 2005).

absolute age. The geologic age of a fossil, rock, feature, 

or event in years; commonly refers to radiometrically 

determined ages.

active margin. A tectonically active margin where 

lithospheric plates come together (convergent 

boundary), pull apart (divergent boundary) or slide 

past one another (transform boundary). Typically 

associated with earthquakes and, in the case of 

convergent and divergent boundaries, volcanism. 

Compare to “passive margin.”

alluvium. Stream-deposited sediment.

alpine glacier. A glacier occurring in a mountainous 

region; also called a valley glacier.

amygdule. A gas cavity or vesicle in an igneous rock, 

which is filled with secondary minerals.

andesite. Volcanic rock commonly associated with 

subduction zone volcanoes. Named for the subduction 

zone volcanoes of the Andes Mountains.

aphanitic. Describes the texture of fine-grained igneous 

rocks where the different components are not 

distinguishable with the unaided eye.

ash (volcanic). Fine pyroclastic material ejected from a 

volcano (also see “tuff”).

authigenic. Describes rocks or minerals that have not 

been transported from where they formed.

basalt. A dark-colored, often low-viscosity, extrusive

igneous rock.

basement. The undifferentiated rocks, commonly 

igneous and metamorphic, that underlie rocks 

exposed at the surface.

basin (sedimentary). Any depression, from continental 

to local scales, into which sediments are deposited.

basin (structural). A doubly-plunging syncline in which 

rocks dip inward from all sides (also see dome).

batholith. A massive, discordant pluton, larger than 100 

km2 (40 mi2

), and often formed from multiple 

intrusions of magma.

bed. The smallest sedimentary strata unit, commonly 

ranging in thickness from one centimeter to a meter or 

two and distinguishable from beds above and below.

bedding. Depositional layering or stratification of 

sediments.

block (fault). A crustal unit bounded by faults, either 

completely or in part.

breccia. A coarse-grained, generally unsorted 

sedimentary rock consisting of cemented angular 

clasts greater than 2 mm (0.08 in).

calcareous. Describes rock or sediment that contains the 

mineral calcium carbonate (CaCO3).

calcic. Describes minerals and igneous rocks containing 

a relatively high proportion of calcium.

caldera. A large bowl- or cone-shaped depression at the 

summit of a volcano. Formed by explosion or collapse.

carbonaceous. Describes a rock or sediment with 

considerable carbon content, especially organics, 

hydrocarbons, or coal.

cementation. Chemical precipitation of material into 

pores between grains that bind the grains into rock.

chemical sediment. A sediment precipitated directly 

from solution (also called nonclastic).

cirque. A deep, steep-walled, half-bowl-like recess or 

hollow located high on the side of a mountain and 

commonly at the head of a glacial valley. Produced by 

the erosive activity of a mountain glacier.

clastic. Describes rock or sediment made of fragments of 

pre-existing rocks (clasts).

clay. Can be used to refer to clay minerals or as a 

sedimentary fragment size classification (less than 

1/256 mm [0.00015 in]).

clinopyroxene. A group name for pyroxene minerals

crystallizing in the monoclinic system.

conglomerate. A coarse-grained, generally unsorted, 

sedimentary rock consisting of cemented, rounded 

clasts larger than 2 mm (0.08 in).

continental crust. Crustal rocks rich in silica and alumina 

that underlie the continents; ranging in thickness from 

35 km (22 mi) to 60 km (37 mi) under mountain ranges.

continental shield. A continental block of Earth’s crust 

that has remained relatively stable over a long period 

of time and has undergone minor warping compared 

to the intense deformation of bordering crust.

convergent boundary. A plate boundary where two 

tectonic plates are colliding.

cordillera. A Spanish term for an extensive mountain 

range; used in North America to refer to all of the 

western mountain ranges of the continent.

country rock. The rock surrounding an igneous intrusion 

or pluton. Also, the rock enclosing or traversed by a 

mineral deposit.

craton. The relatively old and geologically stable interior 

of a continent (also see “continental shield”).

crust. Earth’s outermost compositional shell, 10 to 40 km 

(6 to 25 mi) thick, consisting predominantly of 

relatively low-density silicate minerals (also see 

“oceanic crust” and “continental crust”).

cryptocrystalline. Describes a rock texture where 

individual crystals are too small to be recognized and 

separately distinguished with an ordinary microscope.

crystalline. Describes a regular, orderly, repeating 

geometric structural arrangement of atoms.

dacite. A fine-grained extrusive igneous rock similar to 

andesite but with less calcium-plagioclase minerals and 

more quartz.
36 NPS Geologic Resources Division

deformation. A general term for the process of faulting, 

folding, and shearing of rocks as a result of various 

Earth forces such as compression (pushing together) 

and extension (pulling apart).

dextral fault. See “strike-slip fault.”

diamictite. Poorly sorted, noncalcareous, sedimentary 

rock with a wide range of particle sizes.

dike. A narrow igneous intrusion that cuts across 

bedding planes or other geologic structures.

dip. The angle between a bed or other geologic surface 

and horizontal.

dip-slip fault. A fault with measurable offset where the 

relative movement is parallel to the dip of the fault.

divergent boundary. An active boundary where tectonic 

plates are moving apart (e.g., a spreading ridge or 

continental rift zone).

drainage basin. The total area from which a stream 

system receives or drains precipitation runoff.

drift. All rock material (clay, silt, sand, gravel, boulders) 

transported by a glacier and deposited directly by or 

from the ice, or by running water emanating from a 

glacier.

epiclastic rock. A rock formed at Earth’s surface by 

consolidation of fragments of pre-existing rocks.

extrusive. Describes igneous material that has erupted 

onto Earth’s surface.

fault. A break in rock along which relative movement has 

occurred between the two sides.

feldspar. A group of abundant (more than 60% of Earth’s 

crust), light-colored to translucent silicate minerals 

found in all types of rocks. Usually white and gray to 

pink. May contain potassium, sodium, calcium, 

barium, rubidium, and strontium along with 

aluminum, silica, and oxygen.

felsic. Describes an igneous rock having abundant lightcolored minerals such as quartz, feldspars, or 

muscovite. Compare to “mafic”.

flat slab subduction. Refers to a tectonic plate being 

subducted beneath another tectonic plate at a 

relatively shallow angle.

footwall. The mass of rock beneath a fault surface (also 

see “hanging wall”).

formation. Fundamental rock-stratigraphic unit that is 

mappable, lithologically distinct from adjoining strata, 

and has definable upper and lower contacts.

fracture. Irregular breakage of a mineral. Any break in a 

rock (e.g., crack, joint, fault).

gabbro. A group of dark-colored, intrusive igneous 

rocks. The intrusive equivalent of basalt. 

glacial erratic. Boulders transported by glaciers some 

distance from their point of origin.

granite. A plutonic (intrusive) rock that has large crystals 

of quartz (10–50%) and potassium and sodium-rich 

feldspar (65–90%). Mica and amphibole minerals are 

also common.

granoblastic. Describes the texture of a metamorphic 

rock in which recrystallization formed crystals of 

nearly the same size in all directions.

granodiorite. A group of plutonic rocks containing 

quartz, plagioclase, and potassium feldspar minerals 

with biotite, hornblende, or, more rarely, pyroxene, as 

the mafic components.

hanging wall. The mass of rock above a fault surface 

(also see “footwall”).

hornfels. A fine-grained rock composed of a mosaic of 

same-sized grains without preferred orientation; 

typically formed by contact metamorphism 

(metamorphism taking place in rocks at or near the 

contact with a body of igneous rock).

hypabyssal. An igneous rock formed at a shallow depth. 

igneous. Refers to a rock or mineral that originated from 

molten material; one of the three main classes of 

rocks—igneous, metamorphic, and sedimentary.

intrusion. A body of igneous rock that invades (pushes 

into) older rock. The invading rock may be a plastic 

solid or magma.

joint. A break in rock without relative movement of rocks 

on either side of the fracture surface.

landslide. Any process or landform resulting from rapid, 

gravity-driven mass movement.

latite. A porphyritic extrusive volcanic rock having large 

crystals of plagioclase and potassium feldspar minerals 

in nearly equal amounts, little or no quartz, and a finely 

crystalline to glassy groundmass. 

lava. Still-molten or solidified magma that has been 

extruded onto Earth’s surface though a volcano or 

fissure.

left lateral fault. See “strike-slip fault.”

leucogranite. A light colored intrusive igneous rock rich 

in potassium feldspar and aluminum. 

lithic. A sedimentary rock or pyroclastic deposit that 

contains abundant fragments of previously formed 

rocks.

lithification. The conversion of sediment into solid rock.

lithology. The physical description or classification of a 

rock or rock unit based on characters such as its color, 

mineral composition, and grain size.

lithosphere. The relatively rigid outmost shell of Earth’s 

structure, 50 to 100 km (31 to 62 miles) thick, that 

encompasses the crust and uppermost mantle.

mafic. Describes dark-colored rock, magma, or minerals 

rich in magnesium and iron. Compare to “felsic.”

magma. Molten rock beneath Earth’s surface capable of 

intrusion and extrusion. 

mantle. The zone of Earth’s interior between the crust 

and core.

matrix. The fine grained material between coarse (larger) 

grains in igneous rocks or poorly sorted clastic 

sediments or rocks. Also refers to rock or sediment in 

which a fossil is embedded.

metamorphic. Describes the process of metamorphism 

or its results. One of the three main classes of rocks—

igneous, metamorphic, and sedimentary.

metamorphism. Literally, a change in form. 

Metamorphism occurs in rocks through mineral 

alteration, formation, and/or recrystallization from 

increased heat and/or pressure.

metavolcanic. An informal term for volcanic rocks that 

show evidence of metamorphism.

mid-ocean ridge. The continuous, generally submarine

and volcanically active mountain range that marks the 

divergent tectonic margin(s) in Earth’s oceans.

migmatite. Literally, “mixed rock” with both igneous and 

metamorphic characteristics due to partial melting 

during metamorphism.
DEPO Geologic Resources Inventory Report 37

migmatization. The formation of a migmatite.

mineral. A naturally occurring, inorganic crystalline solid 

with a definite chemical composition or compositional 

range.

monzonite. A group of plutonic (intrusive igneous) rocks 

of intermediate color containing approximately equal 

amounts of alkali feldspar and plagioclase, little or no 

quartz, and commonly augite as the main mafic 

mineral. Intrusive equivalent of latite. 

moraine. A mound, ridge, or other distinct accumulation 

of unsorted, unstratified glacial drift, predominantly 

till, deposited by glacial ice movement.

normal fault. A dip-slip fault in which the hanging wall 

moves down relative to the footwall.

oceanic crust. Earth’s crust formed at spreading ridges 

that underlies the ocean basins. Oceanic crust is 6 to 7 

km (3 to 4 miles) thick and generally of basaltic 

composition.

orogeny. A mountain-building event.

outcrop. Any part of a rock mass or formation that is 

exposed or “crops out” at Earth’s surface.

paleogeography. The study, description, and 

reconstruction of the physical landscape from past 

geologic periods.

Pangaea. A theoretical, single supercontinent that 

existed during the Permian and Triassic periods.

parent rock. The original rock from which a 

metamorphic rock was formed. Can also refer to the 

rock from which a soil was formed.

passive margin. A margin where no plate-scale 

tectonism is taking place; plates are not converging, 

diverging, or sliding past one another. An example is 

the east coast of North America. (also see “active 

margin”).

pebble. Generally, small rounded rock particles from 4 to 

64 mm (0.16 to 2.52 in) in diameter.

pelitic. Describes a sedimentary rock composed of clay 

(pelite) or a metamorphic rock derived by 

metamorphism of a pelite.

phenocryst. A coarse (large) crystal in a porphyritic

igneous rock.

plate tectonics. The concept that the lithosphere is 

broken up into a series of rigid plates that move over 

Earth’s surface above a more fluid asthenosphere.

platy. Refers to a sedimentary particle whose length is 

more than 3 times its thickness. Also refers to a 

sandstone or limestone that splits into thin layers

having thicknesses in the range of 2 to 10 mm (0.08 to 

0.4 in).

pluton (plutonic). A body of intrusive igneous rock that

crystallized at some depth beneath Earth’s surface.

porphyry. An igneous rock consisting of abundant coarse 

crystals in a fine-grained matrix.

potassium feldspar. A feldspar mineral rich in potassium 

(e.g., orthoclase, microcline, sanidine, adularia).

pumice. Solidified “frothy” lava. It is highly vesicular and 

has very low density.

pumiceous. Volcanic vesicular texture involving tiny gas 

holes such as in pumice. Finer than scoriaceous.

pyroclastic. Describes clastic rock material formed by 

volcanic explosion or aerial expulsion from a volcanic 

vent; also pertaining to rock texture of explosive 

origin. In the plural, the term is used as a noun.

pyroxene. A common rock-forming mineral. It is 

characterized by short, stout crystals. 

radiometric age. An age expressed in years and 

calculated from the quantitative determination of 

radioactive elements and their decay products. 

regression. A long-term seaward retreat of the shoreline 

or relative fall of sea level.

relative dating. Determining the chronological 

placement of rocks, events, or fossils with respect to 

the geologic time scale and without reference to their 

numerical age.

reverse fault. A contractional high-angle (greater than 

45°

) dip-slip fault in which the hanging wall moves up 

relative to the footwall (also see “thrust fault”).

rhyodacite. A now-obsolete term for volcanic rock 

intermediate between rhyolite and dacite. 

rhyolite. A group of extrusive volcanic rocks, typically 

porphyritic and commonly exhibiting flow texture, 

with phenocrysts of quartz and alkali feldspar in a 

glassy to cryptocrystalline groundmass. The finegrained extrusive equivalent of granite.

right lateral fault. See “strike-slip fault.”

rock. A solid cohesive aggregate of one or more minerals.

rouche moutonnée. An elongate, eroded ridge or knob of 

bedrock carved by a glacier parallel to the direction of 

motion with gentle upstream and steep downstream 

surfaces.

sandstone. Clastic sedimentary rock of predominantly 

sand-sized grains.

scarp. A steep cliff or topographic step resulting from 

displacement on a fault, or by mass movement, or 

erosion. Also called an “escarpment.”

schist. A strongly foliated metamorphic rock that can be 

readily be split into thick flakes or slabs. Micas are 

arranged in parallel, imparting a distinctive sheen, or 

“schistosity” to the rock.

schistose. A rock displaying schistosity, or foliation.

scoria. A bomb-size pyroclast that is irregular in form 

and generally very vesicular.

scoriaceous. Volcanic igneous vesicular texture 

involving relatively large gas holes such as in vesicular 

basalt. Coarser than pumiceous.

seafloor spreading. The process by which tectonic plates 

pull apart and new lithosphere is created at oceanic 

ridges.

sediment. An eroded and deposited, unconsolidated 

accumulation of rock and mineral fragments.

sedimentary rock. A consolidated and lithified rock 

consisting of clastic and/or chemical sediment(s). One 

of the three main classes of rocks—igneous, 

metamorphic, and sedimentary.

shale. A clastic sedimentary rock made of clay-sized 

particles that exhibit parallel splitting properties.

sierra. An often-used Spanish term for a rugged 

mountain range.

silt. Clastic sedimentary material intermediate in size 

between fine-grained sand and coarse clay (1/256 to 

1/16 mm [0.00015 to 0.002 in]).

siltstone. A variably lithified sedimentary rock composed 

of silt-sized grains.

sinistral fault. See “strike-slip fault.”

slope. The inclined surface of any geomorphic feature or 

measurement thereof. Synonymous with “gradient.”
38 NPS Geologic Resources Division

sodic. Pertaining to minerals and igneous rocks 

containing a relatively high proportion of sodium.

stock. An igneous intrusion exposed at the surface; <100 

km2 (40 mi2

) in size.

strata. Tabular or sheet-like masses or distinct layers of 

rock.

striations. Parallel scratches or lines.

strike. The compass direction of the line of intersection 

of an inclined surface with a horizontal plane.

strike-slip fault. A fault with measurable offset where the 

relative movement is parallel to the strike of the fault.

Said to be “sinistral” (left-lateral) if relative motion of 

the block opposite the observer appears to be to the 

left. “Dextral” (right-lateral) describes relative motion 

to the right.

subduction zone. A convergent plate boundary where 

oceanic lithosphere descends beneath a continental or 

oceanic plate and is carried down into the mantle.

subsidence. The gradual sinking or depression of part of 

Earth’s surface.

tectonic. Relating to large-scale movement and 

deformation of Earth’s crust.

terrane. A large region or group of rocks with similar 

geology, age, or structural style.

terrestrial. Relating to land, Earth, or its inhabitants.

thrust fault. A contractional dip-slip fault with a 

shallowly dipping fault surface (less than 45°

) where 

the hanging wall moves up and over relative to the 

footwall.

till. Unstratified drift, deposited directly by a glacier 

without reworking by meltwater, and consisting of a 

mixture of clay, silt, sand, gravel, and boulders ranging 

widely in size and shape.

topography. The general morphology of Earth’s surface, 

including relief and locations of natural and 

anthropogenic features.

transcurrent fault. A term for a continental strike-slip 

fault that does not terminate at lithospheric plate 

boundaries.

transform fault. A strike-slip fault that links two other 

faults or two other plate boundaries (e.g. two segments 

of a mid-ocean ridge). A type of plate boundary at 

which lithosphere is neither created nor destroyed, 

and plates slide past each other on a strike-slip fault.

transgression. Landward migration of the sea as a result 

of a relative rise in sea level.

transpression. A system of stresses that tends to cause

oblique shortening (combined shortening and strikeslip).

transpressional fault. A strike-slip fault across which 

there is a component of shortening.

transtension. A system of stresses that tends to cause 

oblique extension. Combined extension and strike slip 

faulting.

trend. The direction or azimuth of elongation of a linear 

geologic feature.

tuff. Generally fine-grained, igneous rock formed of 

consolidated volcanic ash.

unconformity. An erosional or non-depositional surface 

bounded on one or both sides by sedimentary strata 

that marks a period of missing time.

undercutting. The removal of material at the base of a 

steep slope or cliff or other exposed rock by the 

erosive action of falling or running water (such as a 

meandering stream), of sand-laden wind in the desert, 

or of waves along the coast.

uplift. A structurally high area in the crust, produced by 

movement that raises the rocks.

vent. An opening at Earth’s surface where volcanic 

materials emerge.

vesicular. Describes a volcanic rock with abundant holes 

that formed from the expansion of gases while the lava 

was still molten.

vitric. Describes pyroclastic material that is 

characteristically glassy.

volcanic. Describes anything related to volcanoes. Can 

refer to igneous rock crystallized at or near Earth’s 

surface (e.g., lava).

weathering. The physical, chemical, and biological 

processes by which rock is broken down.
DEPO Geologic Resources Inventory Report 39

Literature Cited

This section lists references cited in this report. A more complete geologic bibliography is 

available from the National Park Service Geologic Resources Division.

Anderson, T. H. and L. T. Silver. 2005. The MojaveSonora megashear; field and analytical studies leading to 

the conception and evolution of the hypothesis. Special 

Paper 393. Boulder, CO: Geological Society of 

America.

Archuleta, R. J., E. Cranswick, C. Mueller, and P. 

Spudich. 1982. Source parameters of the 1980 

Mammoth Lakes, California, earthquake sequence. 

Journal of Geophysical Research 87: 4585-4607.

Cassel, E. J., S. A. Graham, and C. P. Chamberlain. 2009. 

Cenozoic tectonic and topographic evolution of the 

northern Sierra Nevada, California, through stable 

isotope paleoaltimetry in volcanic glass. Geology 37 (6): 

547-550.

Chamberlain, C. P. and M. A. Poage. 2000. 

Reconstructing the paleotopography of mountain belts 

from the isotopic composition of authigenic minerals. 

Geology 28 (2): 115-118.

Chamberlain, C. P., D. Sjostrom, M. Poage, and T. 

Horton. 2002. Cenozoic topography of the western 

United States. Geological Society of America Abstracts 

with Programs 34 (6): 62.

Chamberlain, C. P., A. Mulch, T. W. Horton, M. L. KentCorson, L. S. Sherman, S. Davis, M. Hren, and C. 

Teyssier. 2005. The Cenozoic rise and fall of the 

Western United States. Eos, Transactions, American 

Geophysical Union 86 (52): Suppl.

Christiansen II, E., B.J. Kowallis, and M.D. Barton. 1994. 

Temporal and spatial distribution of volcanic ash in 

Mesozoic sedimentary rocks of the Western Interior: 

an alternative record of Mesozoic magmatism. In 

Mesozoic systems of the Rocky Mountain region, USA, 

ed. M. V. Caputo, J. A. Peterson, and K. J. Franczyk, 

73-94. Denver, CO: Rocky Mountain Section, Society

for Sedimentary Geology.

Clow, D. W. and K. R. Collum. 1983. Geology of volcanic 

rocks of the Devils Postpile National Monument and 

vicinity, Sierra Nevada, California. Mammoth Lakes, 

CA: Unpublished report on file at Devils Postpile 

National Monument.

DeCelles, P. G. 2004. Late Jurassic to Eocene evolution 

of the Cordilleran thrust belt and foreland basin 

system, western U.S.A. American Journal of Science 304 

(2): 105-168.

Dickinson, W. R. 1977. Paleozoic plate tectonics and the 

evolution of the Cordilleran continental margin. In 

Paleozoic paleogeography of the western United States, 

ed. J. H. Stewart, C. H. Stevens, and A. E. Fritsche, 137-

156. Los Angeles, CA: Society of Economic 

Paleontologists and Mineralogists, Pacific Section, 

Pacific Coast Paleogeography Symposium I.

Dubiel, R. F. 1994. Triassic deposystems, 

paleogeography, and paleoclimate of the Western 

Interior. In Mesozoic systems of the Rocky Mountain 

region, USA, ed. M. V. Caputo, J. A. Peterson, and K. J. 

Franczyk, 133-168. Denver, CO: Rocky Mountain 

Section, Society for Sedimentary Geology.

Dunston, J. F., C. J. Northrup, and W. S. Snyder. 2001. 

Post-latest Triassic thrust emplacement of the 

Golconda allochthon, Sonoma Range, Nevada. 

Geological Society of America Abstracts with Programs

33 (6): 327. http://gsa.confex.com/gsa/2001AM/

finalprogram/abstract_22392.htm. 

Erslev, E. A. 1993. Thrusts, back-thrusts, and detachment 

of Rocky Mountain foreland arches. In Laramide 

basement deformation in the Rocky Mountain foreland 

of the western United States, ed. C. J. Schmidt, R. B. 

Chase, and E. A. Erslev, 339-358. Special Paper 280. 

Boulder, CO: Geological Society of America.

Fiske, R. S. and O. T. Tobisch. 1978. Paleogeographic 

significance of volcanic rocks of the Ritter Range 

pendant, central Sierra Nevada, California. In Mesozoic 

paleogeography of the western United States, ed. D. G. 

Howell and K. A. McDougall, 209-222. Los Angeles, 

CA: Pacific Section, Society of Economic 

Paleontologists and Mineralogists, Pacific Coast 

Paleogeography Symposium 2.

Gries, R. 1983. North-south compression of Rocky 

Mountain foreland structures. In Rocky Mountain 

foreland basins and uplifts, ed. J. D. Lowell and R. 

Gries, 9-32. Rocky Mountain Association of 

Geologists.

Haenggi, W. T. and W. R. Muehlberger. 2005. Chihuahua 

Trough; a Jurassic pull-apart basin. Special Paper 393. 

Boulder, CO: Geological Society of America.

Hamilton, W. 1978. Mesozoic tectonics of the Western 

United States. In Mesozoic paleogeography of the 

western United States, ed D. G. Howell and K. A. 

McDougall, 33-70. Los Angeles, CA: Pacific Section, 

Society of Economic Paleontologists and 

Mineralogists, Pacific Coast Paleogeography 

Symposium 2.
40 NPS Geologic Resources Division

Harp, E. L., K. Tanaka, J. Sarmiento, and D. K. Keefer. 

1984. Landslides from the May 25-27, 1980, Mammoth 

Lakes, California, earthquake sequence. Scale 1:62,500. 

Miscellaneous Investigations Series I-1612. Reston, 

VA: U. S. Geological Survey.

Huber, N. K. 1987. The geologic story of Yosemite 

National Park. Bulletin 1595. Reston, VA: U.S. 

Geological Survey. http://www.yosemite.ca.us/library/

geologic_story_of_yosemite/. 

Huber, N. K. and W. W. Eckhardt. 2002. The story of 

Devils Postpile. Three Rivers, CA: Sequoia Natural 

History Association.

Huber, N.K. and C.D. Rinehart. 1965. Geologic map of the 

Devils Postpile quadrangle, Sierra Nevada, California. 

Scale 1:62,500. Geologic Quadrangle GQ-437. Reston, 

VA: U.S. Geological Survey.

Johnson, J. G., C. A. Sandberg, and F. G. Poole. 1991. 

Devonian lithofacies of western United States. In 

Paleozoic paleogeography of the western United States –

II, ed. J. D. Cooper and C. H. Stevens, 83-106. Los 

Angeles, CA: Society of Economic Paleontologists and 

Mineralogists , Pacific Section I.

Kiver, E. P. and D. V. Harris. 1999. Geology of U.S. 

Parklands. 5th ed. New York: John Wiley & Sons, Inc.

Kluth, C. F. 1983. Geology of the northern Canelo Hills 

and implications for the Mesozoic tectonics of 

southeastern Arizona. In Mesozoic paleogeography of 

west-central United States, ed. M. W. Reynolds and E.

D. Dolly, 159-171. Denver, CO: Society of Economic 

Paleontologists and Mineralogists, Rocky Mountain 

Section, Symposium 2.

Lageson, D. R. and J. G. Schmitt. 1994. The Sevier 

orogenic belt of the western United States: Recent 

advances in understanding its structural and 

sedimentologic framework. In Mesozoic systems of the 

Rocky Mountain region, USA, ed. M. V. Caputo, J. A. 

Peterson, and K. J. Franczyk, 27-65. Denver, CO: 

Rocky Mountain Section, Society for Sedimentary 

Geology.

Lawton, T. F. 1994. Tectonic setting of Mesozoic 

sedimentary basins, Rocky Mountain region, United 

States. In Mesozoic systems of the Rocky Mountain 

region, USA, ed. M. V. Caputo, J. A. Peterson, and K. J. 

Franczyk, 1-26. Denver, CO: Rocky Mountain Section, 

Society for Sedimentary Geology.

Lillie, R. J. 2005. Parks and Plates: The geology of our 

national parks, monuments, and seashores. New York, 

NY: W. W. Norton and Company.

Livaccarvi, R. F. 1991. Role of crustal thickening and 

extensional collapse in the tectonic evolution of the 

Sevier-Laramide Orogeny, western United States. 

Geology 19: 1104-1107.

Mahood, G. A., J. H. Ring, and M. McWilliams. 2000. 

Contemporaneous mafic and silicic eruptions during 

the past 160 ka at Long Valley Caldera, California:

implications of new 40Ar/39Ar eruption ages for 

current volcanic hazards. Eos, Transactions, American 

Geophysical Union 81 (48): 1321.

Matthes, F. E. 1930. Geologic history of the Yosemite 

Valley. Professional Paper 160. Reston, VA: U. S. 

Geological Survey. http://www.nps.gov/history/

history/online_books/geology/publications/pp/160/se

c2a.htm. 

Miller, C. D. 1989. Potential hazards from future volcanic 

eruptions in California. Bulletin 1847. Reston, VA: U. S.

Geological Survey. http://vulcan.wr.usgs.gov/

Volcanoes/California/Hazards/Bulletin1847. 

Mulch, A., S. A. Graham, and C. P. Chamberlain. 2005. 

Topography of the Eocene Sierra Nevada: evidence 

from stable isotopes of kaolinite in paleo-stream 

chanels. Geological Society of America Abstracts with 

Programs 37 (4): 87.

Mulch, A., S. A. Graham, and C. P. Chamberlain. 2006. 

Hydrogen isotopes in Eocene river gravels and 

paleoelevation of the Sierra Nevada. Science 313 

(5783): 87-89.

Oldow, J. S., A. W. Bally, H. G. Avé Lallemant, and W. P. 

Leeman. 1989. Phanerozoic evolution of the North 

American Cordillera: United States and Canada. In The 

geology of North America: An overview, ed. A. W. Bally 

and A. R. Palmer, 139-232. Boulder, CO: Geological 

Society of America, The Geology of North America-A.

Park, S. K., B. Hirasuna, G.R. Jiracek, and C.L Kinn. 

1996. Magnetotelluric evidence of lithospheric mantle 

thinning beneath the southern Sierra Nevada. Journal 

of Geophysical Research 101: 16241-16255.

Peterson, F. 1994. Sand dunes, sabkhas, streams, and 

shallow seas: Jurassic paleogeography in the southern

part of the Western Interior Basin. In Mesozoic systems 

of the Rocky Mountain region, USA, ed. M. V. Caputo, J. 

A. Peterson, and K. J. Franczyk, 233-272. Denver, CO: 

Rocky Mountain Section, Society for Sedimentary 

Geology.

Poole, F. G. and C. A. Sandberg. 1977. Mississippian 

paleogeography and tectonics of the western United 

States. In Paleozoic paleogeography of the western 

United States, ed. J. H. Stewart, C. H. Stevens, and A. E.

Fritsche, 67-86. Los Angeles, CA: Society of Economic 

Paleontologists and Mineralogists, Pacific Section, 

Pacific Coast Paleogeography Symposium I.

Ross, C. 1991. Pennsylvanian paleogeography of the 

western United States. In Paleozoic paleogeography of 

the western United States – II, ed. J. D. Cooper and C. H. 

Stevens, 137-148. Los Angeles, CA: Society of 

Economic Paleontologists and Mineralogists, Pacific 

Section.
DEPO Geologic Resources Inventory Report 41

Saleeby, J. B., C. Busby-Spera, J.S. Oldow, G.C. Dunne, 

J.E. Wright, D.S. Cowan, N.W. Walker, and R.W. 

Allmendinger. 1992. Early Mesozoic tectonic 

evolution of the western U.S. Cordillera. In The 

Cordilleran Orogen: conterminous U.S., ed. B. C. 

Burchfiel, P. W. Lipman, and M. L. Zoback, 107-168. 

Boulder, CO: Geological Society of America, The 

Geology of North America-G-3.

Schweickert, R. A. 1978. Triassic and Jurassic 

paleogeography of the Sierra Nevada and adjacent 

regions, California and western Nevada. In Mesozoic 

paleogeography of the western United States, ed. D. G. 

Howell and K. A. McDougall, 361-384. Los Angeles, 

CA: Pacific Section, Society of Economic 

Paleontologists and Mineralogists, Pacific Coast 

Paleogeography Symposium 2.

Stevens, C. H. 1991. Permian paleogeography of the 

western United States. In Paleozoic paleogeography of 

the western United States – II, ed. J. D. Cooper and C. H. 

Stevens, 149-166. Los Angeles, CA: Society of 

Economic Paleontologists and Mineralogists, Pacific 

Section.

Stevens, C. H., P. Stone, and J. S. Miller. 2005. A new 

reconstruction of the Paleozoic continental margin of 

southwestern North America: implications for the nature 

and timing of continental truncation and the possible role 

of the Mojave-Sonora megashear. Special Paper 393.

Boulder, CO: Geological Society of America.

Stewart, J. H. 1991. Latest Proterozoic and Cambrian 

rocks of the western United States – an overview. In 

Paleozoic paleogeography of the western United States –

II, ed. J. D. Cooper and C. H. Stevens, 13-38. Los 

Angeles, CA: Society of Economic Paleontologists and 

Mineralogists, Pacific Section.

Stock, G. M, R. S. Anderson, and R. C. Finkel. 2004. Pace 

of landscape evolution in the Sierra Nevada, 

California, revealed by cosmogenic dating of cave 

sediments. Geology 32 (3): 193-196.

Stock, G. M, R. S. Anderson, and R. C. Finkel. 2005. 

Rates of erosion and topographic evolution of the 

Sierra Nevada, California, inferred from cosmogenic 

(super 26) Al and (super 10) Be concentrations. Earth 

Surface Processes and Landforms 30 (8): 985-1006.

Trexler, Jr., J. H., W. S. Snyder, P. H. Cashman, D. M. 

Gallegos, and C. Spinosa. 1991. In Paleozoic 

paleogeography of the western United States – II, ed. J. D. 

Cooper and C. H. Stevens, 317-329. Los Angeles, CA: 

Society of Economic Paleontologists and 

Mineralogists, Pacific Section.
DEPO Geologic Resources Inventory Report 43

Appendix A: Overview of Digital Geologic Data

The following page is an overview of the digital geologic data for Devils Postpile 

National Monument. For a poster-size PDF of this overview and complete digital data, 

please see the included CD or visit the Geologic Resources Inventory publications web 

site (http://www.nature.nps.gov/geology/inventory/gre_publications.cfm).


DEPO Geologic Resources Inventory Report 45

Appendix B: Scoping Summary

The following excerpts are from the GRI scoping summary for Devils Postpile National 

Monument. The scoping meeting occurred September 25-26, 2002; therefore, the contact 

information and Web addresses referred to herein may be outdated. Please contact the 

Geologic Resources Division for current information.

A Geologic Resources Inventory (GRI) workshop was 

held for Yosemite National Park (YOSE) and Devils 

Postpile National Monument (DEPO) on September 25-

26, 2002. The purpose was to view and discuss the park’s 

geologic resources, to address the status of geologic 

mapping for compiling both paper and digital maps, and 

to assess resource management issues and needs. 

Cooperators from the NPS Geologic Resources Division 

(GRD), YOSE, DEPO, the University of North Carolina, 

and the United States Geologic Survey (USGS) were 

present for the workshop.

This involved field trips to various points of interest in 

YOSE, led by King Huber, as well as another full-day 

scoping session to present overviews of the NPS 

Inventory and Monitoring (I&M) program, the GRD, 

and the on-going GRI. Round table discussions involving 

geologic issues for YOSE and DEPO included the status 

of geologic mapping efforts, interpretation, sources of 

available data, and action items generated from this 

meeting. Because of time and logistical limitations, DEPO 

did not get a site visit during the scoping session.

(The following excerpts involve only Devils Postpile 

National Monument. Information regarding Yosemite 

National Park may be found in the Yosemite National 

Park Geological Resource Evaluation report.)

Existing Geologic Maps and Digital Data

After bibliographies were assembled, a separate search 

was made for any existing surficial and bedrock geologic 

maps for YOSE and DEPO. The USGS has published 

numerous quadrangles in the area at various scales and of 

variable vintage.

DEPO has a published paper map at 1:62,500 scale 

(Huber, N.K.; Rinehart, C.D., 1965, Geologic map of the 

Devils Postpile quadrangle, Sierra Nevada, California, US 

Geological Survey, GQ-437, 1:62500 scale) that 

encompasses four 7.5' quadrangles (Mount Ritter, 

Mammoth Mountain, Crystal Crag, and Cattle 

Mountain). It is not known whether this map has been 

digitized at the present time.

However, a more refined map has been produced by the 

USGS by David Clow and Kenneth Collum. It is not 

known if this map is published, but it was suggested 

during the scoping session to use this map instead of GQ437 for the official park map. Bruce Heise is tracking 

down more information about this map. It is previewed 

in "The Story of Devils Postpile: A Land of Volcanic Fire, 

Glacial Ice and an Ancient River". This publication was 

released by the Sequoia Natural History Association in 

2002.

DEPO Management Needs 

Research projects

• Dating of lava flows

• Monitoring glacial polish

• Ground water chemistry of springs in the 

meadow

• Carbon dioxide flow in the soil and possible 

tree kill

• Hydrology/geomorphology of San Joaquin 

River

• Global climate change relative to species 

diversity (high snowfall now)

• Historic flows of the San Joaquin (contact NPSWater Resources Division)

• Possible effects to DEPO’s springs and 

watershed from proposed ground water 

pumping on San Joaquin ridge

Issues/Hazards

• Need climate summary

Geologic Reports 

• Huber, N. K. 1987. The geologic story of Yosemite 

National Park. Bulletin 1595. Reston, VA: U.S. 

Geological Survey.

• Matthes, F. E. 1930. Geologic history of the 

Yosemite Valley. Professional Paper 160. Reston, 

VA: U.S. Geological Survey.

• Huber, N. K. and Eckhardt, W. W. 2002. The 

story of Devils Postpile: A land of volcanic fire, 

glacial ice and an ancient river. Three Rivers, 

CA: Sequoia Natural History Association.

All reports are written for interpretive needs for the park, 

not technical needs or resource management issues, so 

would need to be enhanced for the purposes of the GRI 

report.
46 NPS Geologic Resources Division

NAME AFFILIATION TITLE PHONE E-MAIL

Allen, Lindy NPS-GRD admin. Assistant 303-969-2090 lindy_allen@Nps.gov

Bumgardner, Steve videographer 559-565-3949 s_bumgardner@hotmail.com

Butler, Mark NPS-YOSE physical scientist 209-379-3260 mark_butler@nps.gov

Connors, Tim NPS, Geologic Resources 

Division geologist (303) 969-2093 Tim_Connors@nps.gov

Despain, Joel NPS-SEKI cave specialist 559-565-3717 joel_despain@nps.gov

Dulen, Deanna NPS-DEPO superintendent 760-934-8100 deanna_dulen@nps.gov

Galipeau, Russell NPS-YOSE chief of cultural 

resources 209-379-1219 russell_galipeau@nps.gov

Glazner, Allan University of North Carolina at 

Chapel Hill professor 919-962-0689 afg@unc.edu

Gregson, Joe NPS, Natural Resources 

Information Division physical scientist (970) 225-3559 Joe_Gregson@nps.gov

Heise, Bruce NPS, Geologic Resources 

Division geologist (303) 969-2017 Bruce_Heise@nps.gov

Huber, King USGS geologist 650-329-4925 khuber@usgs.gov

Meyer, Joe NPS-YOSE GIS 209-379-1185 joe_meyer@nps.gov

Murchey, Bonnie USGS geologist 650-329-4926 bmurchey@usgs.gov

VanWagtendonk, Jan USGS-WERC research forester 209-379-1306 jan_van_wagtendonk@usgs.gov
Devils Postpile National Monument

Geologic Resources Inventory Report

Natural Resource Report NPS/NRPC/GRD/NRR—2009/160

National Park Service

Director • Jonathan Jarvis

Natural Resource Stewardship and Science

Associate Director • Bert Frost

Natural Resource Program Center

The Natural Resource Program Center (NRPC) is the core of the NPS Natural Resource Stewardship and 

Science Directorate. The Center Director is located in Fort Collins, with staff located principally in Lakewood 

and Fort Collins, Colorado and in Washington, D.C. The NRPC has five divisions: Air Resources Division, 

Biological Resource Management Division, Environmental Quality Division, Geologic Resources Division, and 

Water Resources Division. NRPC also includes three offices: The Office of Education and Outreach, the Office 

of Inventory, Monitoring, and Evaluation, and Office of Natural Resource Information Systems. In addition, 

Natural Resource Web Management and Partnership Coordination are cross-cutting disciplines under the 

Center Director. The multidisciplinary staff of NRPC is dedicated to resolving park resource management 

challenges originating in and outside units of the National Park System.

Geologic Resources Division

Chief • Dave Steensen

Planning, Evaluation, and Permits Branch Chief • Carol McCoy

Geoscience and Restoration Branch Chief • Hal Pranger

Credits

Author • John Graham

Review • Alan Glazner and Bruce Heise

Editing • Bonnie Dash

Digital Map Production • Greg Mack and Stephanie O’Meara

Map Layout Design • Josh Heise and Georgia Hybels

The Department of the Interior protects and manages the nation’s natural resources and cultural heritage; provides scientific and other 

information about those resources; and honors its special responsibilities to American Indians, Alaska Natives, and affiliated Island 

Communities

NPS 120/100620, December 2009
EXPERIENCE YOUR AMERICATM 

Geologic Resources Division 

Natural Resource Program Center 

P.O. Box 25287 

Denver, CO 80225 

www.nature.nps.gov 

National Park Service 

U.S. Department of the Interior