Chiricahua National Monument 

Geologic Resources Inventory Report 

Natural Resource Report NPS/NRPC/GRD/NRR—2009/081 

National Park Service 

U.S. Department of the Interior 

Natural Resource Program Center 
THIS PAGE: THIS PAGE: 

Close up of the many rhyolitic hoodoos Close up of the many rhyolitic hoodoos 

within the Monument within the Monument

ON THE COVER: ON THE COVER: 

Scenic vista in Chiricahua NM Scenic vista in Chiricahua NM

NPS Photos by: Ron Kerbo NPS Photos by: Ron Kerbo 
Chiricahua National Monument 

Geologic Resources Inventory Report 

Natural Resource Report NPS/NRPC/GRD/NRR—2009/081 

Geologic Resources Division 

Natural Resource Program Center 

P.O. Box 25287 

Denver, Colorado 80225 

June 2009 

U.S. Department of the Interior 

National Park Service 

Natural Resource Program Center 

Denver, Colorado
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the back cover. 

Please cite this publication as: 

Graham, J. 2009. Chiricahua National Monument Geologic Resources Inventory Report. 

Natural Resource Report NPS/NRPC/GRD/NRR—2009/081. National Park Service, Denver, 

Colorado. 

NPS D-94, June 2009 

ii 
CHIR Geologic Resource Inventory Report iii 

Contents 

Figures .......................................................................................................................... iv

Executive Summary ...................................................................................................... 1

Introduction ................................................................................................................... 2

Purpose of the Geologic Resources Inventory ........................................................................................................... 2

Regional and Geologic Setting ................................................................................................................................... 2

Park History ................................................................................................................................................................ 3

Geologic Issues ............................................................................................................. 6

Flooding ...................................................................................................................................................................... 6

Mass Wasting and Hoodoo Stability ........................................................................................................................... 6

Information for Interpretation ...................................................................................................................................... 7

Other Issues ............................................................................................................................................................... 7

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

Features Related to Differential Weathering and Erosion ......................................................................................... 11

Volcanic Features Related to the Turkey Creek Caldera .......................................................................................... 13

Features that Predate the Turkey Creek Caldera ..................................................................................................... 14

Structural Features ................................................................................................................................................... 15

Map Unit Properties .................................................................................................... 18

Map Unit Properties Table ........................................................................................................................................ 19

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

Paleozoic History ...................................................................................................................................................... 23

Mesozoic History ...................................................................................................................................................... 24

Cenozoic History ...................................................................................................................................................... 24

Glossary ....................................................................................................................... 31

References ................................................................................................................... 35

Appendix A: Geologic Map Graphic .......................................................................... 37

Appendix B: Scoping Summary ................................................................................. 39

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

Figures 

Figure 1. Pinnacles, columns, and balanced rocks in the Rhyolite Canyon Tuff in Chiricahua NM ................................ 3

Figure 2. Location map for Chiricahua National Monument ........................................................................................... 4 

Figure 3. General stratigraphic column for Chiricahua National Monument ................................................................... 5

Figure 4. The Visitor Center at Chiricahua National Monument ..................................................................................... 8

Figure 5. Surge deposits and welded tuff deposits ......................................................................................................... 9

Figure 6. Landslide potential ........................................................................................................................................ 10

Figure 7. Surge beds, fumarole pipe, and Liesegang bands ........................................................................................ 16

Figure 8. A fumarole pipe preserved in the Rhyolite Canyon Tuff, Sugarloaf Mountain Trail ....................................... 17

Figure 9. Geologic Timescale....................................................................................................................................... 26

Figure 10. Early Permian paleogeographic map of the southwestern United States .................................................... 27

Figure 11. Early Cretaceous paleogeographic map of the southwestern United States ............................................... 28

Figure 12. Late Cretaceous paleogeographic map of North America ........................................................................... 29

Figure 13. Oligocene paleogeographic map of the southwestern United States .......................................................... 30
CHIR Geologic Resource Inventory Report 1 

Executive Summary 

This report accompanies the digital geologic map for Chiricahua National Monument in 

Arizona, 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. 

The geologic features preserved in Chiricahua National 

Monument are spectacular examples of physical and 

chemical weathering processes. The Monument was 

established in 1924 to protect its distinctive pinnacles, 

columns, spires, and balanced rocks that seem to defy 

gravity. The remarkable rock spires, known as ‘hoodoos,’ 

are erosional features formed in the Rhyolite Canyon 

Tuff. The volcanic eruption that produced the abundant 

Rhyolite Canyon Tuff ejected more than a thousand 

times the amount of material than was ejected during the 

May 1980 Mount St. Helens eruption in Washington 

State. The explosion and collapse of the magma chamber 

formed the giant Turkey Creek caldera, a depression 

19 km (12 mi) across and 1,500 m (5,000 ft) deep. In 

addition to the unusual erosional features, Chiricahua 

National Monument preserves and protects geologically 

significant remnants of the Turkey Creek caldera. 

Located in southeastern Arizona, the Chiricahua 

Mountain Range is an inactive volcanic range 32 km 

(20 mi) wide and 64 km (40 mi) long. It lies within the 

Basin and Range physiographic province of mountain 

ranges separated by fault-bounded, sediment-filled 

basins. Although Paleozoic and Mesozoic sedimentary 

rocks are exposed in Chiricahua National Monument, 

Cenozoic volcanic rocks dominate the landscape. These 

volcanic rocks, weathered into a maze of pinnacles and 

passageways, provided an impenetrable stronghold for 

the Chiricahua Band of the Apache Indian Nation during 

the nineteenth century. 

The most significant geologic issues facing resource 

management at Chiricahua National Monument include 

flooding, mass wasting, and information for 

interpretation. The Visitor Center and the Bonita Creek 

Campground are located at the head of Faraway 

Meadow, a narrow canyon surrounded by steep slopes. 

They lie within the floodplain and are susceptible to 

flooding. The flash flood risk is monitored on a day-byday basis and the campground is closed periodically in 

response to predicted weather conditions. 

Mass wasting occurs along the Sugarloaf Mountain Trail. 

An easily eroded volcanic ash layer undercuts a cliff of 

densely welded tuff, causing potential collapse of the 

overlying rock. Slumps and landslides may present safety 

and maintenance issues for the park. 

In the past, interpretation focused almost exclusively on 

the pinnacles, hoodoos, and unusual geologic formations 

in the Monument, ignoring the dynamic history of the 

Turkey Creek caldera. This report provides information 

that may be used to help develop programs and exhibits 

that better explain the whole geologic story at Chiricahua 

National Monument. The interpretive displays at 

Sugarloaf Mountain, for example, could be revised to 

more accurately explain the exceptional volcanic 

eruption that produced the Rhyolite Canyon Tuff. 

Additional geologic issues include acid mine drainage 

from the King of Lead Mine, illegal mineral and 

specimen collecting, and soil and groundwater 

contamination from an underground storage tank that 

leaked in 1994. Stability of the pinnacles and balanced 

rocks is not an issue for management. Although the 

slender pinnacles appear ready to collapse, studies show 

that the hoodoos and spires are remarkably stable. 

Features associated with volcanic activity, regional 

tectonic deformation, and weathering processes are 

displayed in Chiricahua National Monument. 

Weathering and erosion processes have created slot 

canyons, slumps, a natural bridge, solution pans, rock 

varnish, tafoni, spherulites, and inverted topography in 

addition to the Monument’s distinctive pinnacles, spires, 

balanced rocks, and columns. Volcanic features, 

primarily related to the Turkey Creek caldera, include 

the caldera, welded tuff of the Rhyolite Canyon Tuff, 

fiamme, fumarole pipes, moat deposits, surge deposits, 

and igneous dikes. The volcanic features were displaced 

and fractured by steep normal faults that resulted from 

crustal extension during the past 20 million years. 

While much of the geologic history of the Precambrian, 

Paleozoic and Mesozoic eras is absent in Chiricahua 

National Monument, the rocks that are exposed record a 

dynamic Cenozoic history of volcanic eruptions. 

Remnants of the Turkey Creek caldera provide evidence 

for three successive large volcanic eruptions beginning 

about 26.9 million years ago that blasted more than 

400 km3

 (100 mi3) of magma from a buried magma 

chamber and covered a region of at least 3,100 km2

(1,200 mi2

) with pyroclastic debris. Volcanic ash, glowing 

gas cloud deposits, steam vents, lava flows, and highvelocity surge deposits can be found in Chiricahua 

National Monument. Hot glass shards fused together to 

form the welded tuff of the Rhyolite Canyon Tuff, a 

deposit at least 490 m (1,600 ft) thick. Upon cooling, 

vertical joints formed in the erosion-resistant Rhyolite 

Canyon Tuff and provided conduits for water. Continual 

freezing and thawing expanded the joints and dislodged 

pieces of the rock. Over time, chemical and physical 

weathering processes acted together to carve the 

pinnacles, spires, and columns for which the Monument 

is known.
2 NPS Geologic Resources Division 

Introduction 

The following section briefly describes the National Park Service Geologic Resources 

Inventory and the regional geologic setting of Chiricahua 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 and Geologic Setting 

Chiricahua National Monument was established in 1924 

to protect and preserve the exceptional geologic features 

found in the Monument including pinnacles, columns, 

spires and balanced rocks (fig. 1). While these features 

are spectacular examples of physical and chemical 

weathering processes, the monument also preserves 

remnants of the 19-km- (12-mi) diameter Turkey Creek 

caldera that formed about 26.9 million years ago. 

Eruption of the associated volcano produced a volume of 

volcanic material a thousand times larger than that 

produced by the 1980 eruption of Mount St. Helens and 

five to ten times the volume produced by the great 

volcanic explosion of Krakatoa in 1883. The amount of 

molten material erupted from a shallow reservoir in the 

crust was so large that the ground surface collapsed into 

the resulting void, thereby creating the Turkey Creek 

caldera (Pallister et al. 1997). 

The Monument’s 4,850.22 hectares (11,984.73 acres) are 

in the Chiricahua Mountains of extreme southeastern 

Arizona (fig. 2). Chiricahua National Monument is a 

biological crossroads where four different ecological 

regions meet. The convergence of the Sonoran desert, 

Chihuahuan desert, the Rocky Mountain biome, and the 

Sierra Madre biome makes this region unusually diverse 

in both flora and fauna. In 1976, 86% of the Monument 

(4,164 hectares; 10,290 acres) received Wilderness 

designation from Congress. 

The Chiricahua Mountains, a range of inactive volcanoes 

32 km (20 mi) wide by 64 km (40 mi) long, are part of the 

Mexican Highland section of the Basin and Range 

province. Although part of a desert landscape, the ranges 

and basins are relatively higher than those to the west in 

the Sonoran Desert Section of the Basin and Range 

province. Peaks as high as 2,986 m (9,796 ft) receive both 

snow and rain sufficient to support a dense growth of 

vegetation, especially in shaded canyons (Kiver and 

Harris 1999). 

The oldest rocks in the Monument are late Paleozoic, 

Permian limestones about 280 million years old that are 

exposed in fault blocks in the northeast corner of the 

Monument (fig. 3). Volcanic ash and welded tuff 

deposits record a series of explosive eruptions that shook 

the area during the Tertiary and buried Paleozoic and 

Mesozoic sedimentary rocks. Although rocks of the same 

age exist elsewhere in Arizona, the volcanic rocks that 

resulted from eruption of the Turkey Creek volcano are 

found only in the Chiricahua Mountains and 

immediately adjacent areas. 

The complex geologic history of southeastern Arizona 

includes not only volcanic events but also episodes of 

tectonic compression and extension. Convergence of 

lithospheric plates during the Late Cretaceous to middleTertiary cuased the regional folding and thrust faulting 

found in the Chiricahua and Dos Cabezas Mountains to 

the north. Crustal extension during the Cenozoic 

produced normal faults, which border the structural 
CHIR Geologic Resource Inventory Report 3 

basins as well as blocks within the mountain ranges, and 

gave rise to today’s basin and range topography. 

Weathering and other erosion processes over the past 

two million years, especially during the wetter 

Pleistocene Ice Ages, carved the volcanic deposits into 

the maze of columns and passageways that characterize 

Chiricahua National Monument. Chemical and physical 

weathering processes continue to shape the landscape. 

Park History 

The Chiricahua Mountains were part of the traditional 

homeland of the Chiricahua Band of the Apache Indian 

Nation. The Apaches called this part of the Chiricahua 

Mountains “The Land of Standing-Up Rocks.” During 

the conflicts of the nineteenth century between the 

Apaches and the U.S. military, the labyrinth of rock 

pillars and passageways provided an essentially 

impenetrable stronghold for the skillful and effective 

Apache warriors Cochise and Geronimo (Kiver and 

Harris 1999; http://www. nps.gov/chir, accessed March 

2007). 

Upon surrendering at Fort Bowie in 1886, Geronimo and 

the other Apaches were exiled to Florida. Along the way, 

one of his lieutenants, “Bigfoot” Massai, leapt from the 

train and returned to the Chiricahua Mountains where 

he eluded his pursuers for more than 20 years in the 

maze of pinnacles in what is now Chiricahua National 

Monument. He was never caught. Massai Canyon and 

Massai Point derive their names from him. 

After Geronimo surrendered, Swedish immigrants Neil 

and Emma Erickson settled in Bonita Canyon and 

operated the Faraway Ranch, which is now on 

Monument property. Their closest neighbors were the 

Stafford family, whose cabin can be found farther up the 

canyon. Rumor has it that Bigfoot Massai stole a horse 

from the Staffords, rode to Massai Point, and was never 

seen again. 

The Erickson’s daughter and her husband turned 

Faraway Ranch into a guest (“dude”) ranch and worked 

toward making the area into a national park. In 1924, 

President Calvin Coolidge designated Chiricahua 

National Monument. In 1976, Congress designated 86% 

of the monument as Wilderness. When the Faraway 

Ranch property was sold to the National Park Service in 

1979, it became a historic district within the Monument. 

Figure 1. Pinnacles, columns, and balanced rocks in the Rhyolite Canyon Tuff in Chiricahua National Monument, Arizona. Photograph 

by John Graham (Colorado State University), April 5, 2006. 

CHIR Geologic Resource Inventory Report 5 

Era Period Formation/Unit General Lithology CENOZOIC 

Quaternary Alluvium, colluvium Various subdivisions of sand, silt, and 

gravel 

Tertiary 

Conglomerate Poorly sorted fine- and coarse-grained 

sediments 

Rocks of the 

Turkey Creek Caldera 

Moat deposits: mostly rhyolite lava flows 

Dacite of Sugarloaf Mountain: dacite lava 

flow 

Rhyolite Canyon Tuff: welded-ash-flow 

deposit 

Jesse James Canyon Tuff Welded ash-flow deposit

Faraway Ranch Formation Assemblage of rhyolite, dacite, and andesite 

lavas & pyroclastic rocks 

Sedimentary rocks of 

Bonita Park 

Red-weathering clay-rich sandstone, 

siltstone, and claystone 

Welded tuff of 

Joe Glen Ranch Welded rhyolite ash-flow deposit 

Volcanic flows and dikes Andesite and dacite lava flows; rhyolite 

dikes 

Regional Unconformity 

MESOZOIC 

Cretaceous 

Bisbee Group

Mural Limestone Tan, thin-bedded silty limestone 

Bisbee Group

Morita Formation Siltstone, sandstone, shale, conglomerate 

Glance Conglomerate Cobble, pebble, & boulder conglomerate 

Volcaniclastic and volcanic 

rocks 

Metamorphosed greywacke, andesite, and

basalt 

Regional Unconformity 

PALEOZOIC 

Permian 

Concha Limestone Dark-gray, cherty, fossiliferous limestone 

Scherrer Formation Light-gray fine-grained sandstone and 

quartzite 

Epitaph Dolomite and 

Colina Formation 

Dark-gray, coarse-grained slightly cherty 

limestone and light-gray, fine-grained 

dolomite 

Earp Formation Pale-red siltstone and argillaceous 

limestone 

Horquilla Limestone Upper member: limestone and siltstone 

Figure 3. General stratigraphic column for Chiricahua National Monument. Regional unconformities represent major gaps in time 

within the geologic record at the Monument. 
6 NPS Geologic Resources Division 

Geologic Issues 

The National Park Service held a Geologic Resources Inventory scoping session for 

Chiricahua National Monument on April 5, 2006, 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. 

Narrow canyons, intense rainfall events, and easily 

eroded volcanic rock layers contribute to significant 

geologic issues facing Chiricahua National Monument 

resource management. Geological research in the last 15 

years has also exposed a need for improved interpretive 

materials to explain the geologic history of the 

Monument. 

Flooding 

Bonita Canyon, Rhyolite Canyon, Newton Canyon, and 

their tributary canyons drain into Faraway Meadow, 

located in a narrow canyon surrounded on three sides by 

steep slopes (fig. 2) (Pallister and du Bray 1997). Both the 

Chiricahua National Monument Visitor Center and the 

Bonita Creek Campground at the head of Faraway 

Meadow lie within the floodplain (fig. 4). 

Precipitation within the Monument averages 49.58 cm 

(19.52 in) a year, most of which falls during the summer 

monsoons from July through mid-September. Rainfall 

events occur as high intensity thunderstorms. Rocky 

slopes encourage runoff. Because the slopes are so steep, 

any flooding will be sudden and likely preclude 

evacuation (Carrie Dennett, NPS Chiricahua National 

Monument ecologist, personal communication, April 5, 

2006). 

Chiricahua National Monument managers have no plans 

to relocate facilities that currently lie within the 

floodplain, but the Monument may identify areas prone 

to flooding and avoid constructing new facilities in these 

areas. In the past, the campground has been closed due 

to flooding. The flash flood risk will continue to be 

monitored on a daily basis, and selective closures of the 

Bonita Creek Campground will be based on seasonal and 

predicted weather conditions at Chiricahua National 

Monument (National Park Service 2001). 

Mass Wasting and Hoodoo Stability 

Landslides 

An ash-rich, white-to-light gray bed forms a conspicuous 

layer at the contact of the Upper and Middle Members of 

the Rhyolite Canyon Tuff along Sugarloaf Mountain 

Trail (figs. 5). The ash layer is soft and more easily eroded 

than the overlying layers of welded tuff. During wet 

years, water moves along joints and saturates the white 

ash, thereby reducing its strength and causing slumping. 

With undercutting, the overlying cliff becomes unstable 

and collapses (fig. 6) (Pallister and du Bray 1997; Bezy 

2001). Destabilized blocks in the overlying cliffs break 

loose and tumble down the slopes of Sugarloaf 

Mountain. 

A February 2001 landslide closed the Sugarloaf 

Mountain Trail for a year and a half. Management may 

wish to consult a rockfall expert such as Gerry 

Wieczorek (USGS), who has worked with NPS 

personnel on large rockfalls in Yosemite National Park 

(Ed du Bray, USGS geologist, written communication, 

March 12, 2009). Re-routing the trail onto the southern, 

gentler slopes may be an alternative, also. 

The Upper Member of the Rhyolite Canyon Tuff is only 

found atop Sugarloaf Mountain in the Monument. 

Landslide deposits are also mapped in the northeastern 

part of the Monument along East Whitetail Trail 

(Pallister and du Bray 1997). However, these are older, 

relatively stable deposits (Ed du Bray, USGS geologist, 

written communication, March 12, 2009). Landslide 

potential is further reduced because the terrain isn’t too 

steep in this area. In this remote part of the Monument, 

infrastructure is relatively minor and hikers are few. 

Extensive landslide deposits in Pinery Canyon are 

located adjacent to the southeastern boundary of 

Chiricahua National Monument (Pallister and du Bray 

1997). These older deposits lie outside the Monument on 

relatively gentle topography. 

Hoodoo Stability 

Tall, slender pinnacles, like those in Chiricahua National 

Monument, are known as hoodoos and look as if they 

could easily collapse. Balanced rocks, notched where 

horizontal joints have weathered, appear ready to topple. 

However, studies show that the pinnacles could 

withstand 12–13 times their weight in stress before they 

would collapse (Bezy 2001). Engineering analysis of the 

columns shows that the columns are quite strong and 

well within their mechanical failure limits for static load 

(Hall 1996). In fact, columns supporting balanced rocks 

above V-shaped incuts have been shown to be more 

stable than those columns that do not have necks. 

Neither they nor the balanced rocks are about to fail 

under their own weight (Pallister et al. 1997). Even the 

Totem Pole (height 57 m [187 ft]) could be suspended 

upside-down without breaking. 

Dynamic failure, which involves seismic shaking by a 

lateral force, is more likely to topple columns than 

gravity. Earthquakes produce lateral forces, but the 7.2-

M Pitaycachi earthquake in 1887 did relatively little 
CHIR Geologic Resource Inventory Report 7 

damage to the columns in Chiricahua National 

Monument (Hall 1996). The Pitaycachi earthquake, 

whose epicenter was located approximately 120 km (75 

mi) south-southeast of Chiricahua National Monument, 

shook all of southeastern Arizona and caused rockslides 

as far away as the Santa Catalina Mountains north of 

Tucson but did not destabilize the hoodoos. 

When a large rock fell onto the main road after a 

rainstorm, seismometers were placed to monitor 

vibrations from heavy equipment and small dynamite 

charges (Alan Whalon, Chiricahua National Monument 

superintendent, personal communication, April 5, 2006). 

Road maintenance did not destabilize the pinnacles and 

other rock structures, but the study did show that 

climbing on the rocks promoted rockfall. Chiricahua 

National Monument does not allow rock climbing, and 

the study offered additional evidence to support a ban on 

rock climbing in the Monument. 

Information for Interpretation 

At the scoping session, Ed du Bray, U.S. Geological 

Survey geologist, emphasized the need to update the 

interpretive displays at Sugarloaf Mountain. Displays 

currently represent the Turkey Creek volcano as a 

stratovolcano with steep slopes, similar to Mount 

Rainier, for example. However, the Turkey Creek 

caldera resulted from an entirely different type of 

volcanic eruption. 

The Turkey Creek caldera is a product of a large mass of 

rhyolite magma that accumulated near the surface in the 

area south of the Monument. Eventually, the overlying 

rock ruptured, resulting in a decrease in confining 

pressure. As pressure decreased, volatiles (mostly water 

and carbon dioxide) separated from the magma and 

formed gas bubbles. The frothy magma expanded as 

much as 50 times in volume, causing a series of large 

explosive eruptions of pumice and ash (Pallister and du 

Bray 1997). Clouds of ash blanketed a vast area of what is 

today southern Arizona and New Mexico. Dense, hot 

clouds of pumice, ash, and volcanic gases filled the 

Monument valley to a depth of more than 490 m (1,600 

ft). More than 400 km3 (100 mi3) of molten rock erupted 

from the volcano. In comparison, Mount St. Helens 

produced 0.4 km3

 (0.1 mi3) of magma, and the 1991 

eruption of Mount Pinatubo in the Philippines, which 

was one of the largest eruptions of the 20th century, 

produced only about 4 km3 (1 mi3) of magma (Pallister et 

al. 1997). When the magma erupted from Turkey Creek 

volcano, the magma chamber collapsed and the floor of 

the volcano subsided, forming the 19-km (12-mi) 

diameter Turkey Creek caldera. 

The extraordinary volume of volcanic material produced 

by the Turkey Creek volcano is typically associated with 

catastrophic eruptions from stratovolcanoes, such as the 

Mount Mazama eruption that produced the Crater Lake 

caldera, or the more recent eruptions from Mount 

Pinatubo and Mount St. Helens. However, the Turkey 

Creek magma erupted explosively through ring fractures, 

not through a central vent as in a stratovolcano. 

In the past, interpretation at Chiricahua National 

Monument focused on the pinnacles and other unusual 

geological formations rather than the history of the 

Turkey Creek caldera. This report may help the 

interpretive staff at the Monument develop materials and 

programs that present a more accurate and complete 

geologic story. 

Other Issues 

King of Lead Mine 

The King of Lead Mine is located adjacent to the 

northeast boundary of Chiricahua National Monument. 

The mine has four patented mining claims and was active 

until 1984 when access to the mine through the 

Monument became an issue (see Appendix B). The 

primary ore deposits are lead-zinc deposits that formed 

when magma that may be associated with an unknown 

caldera at Cochise Head, northeast of the Monument, 

reacted with Paleozoic rocks. 

The King of Lead Mine and smaller lead-zinc deposits in 

the area cannot be extracted economically in today’s 

market. If economic conditions change and the 

extraction of lead from this mine becomes economic, the 

park may need to work with GRD staff to address 

impacts from adjacent mining. Although this is unlikely 

to occur in the near future, potential impacts from 

renewed mining may include acid mine drainage, impacts 

to the Monument’s viewshed, and access issues. 

The King of Lead Mine drains to Bonita Creek, but there 

is no surface flow for most of the year. Water-quality 

tests of Bonita Creek showed no impacts from acid mine 

drainage, but hydrologist Mike Martin of the NPS Water 

Resources Division was skeptical of these results. 

Groundwater and surface-water sampling may provide 

more definitive information for use in land-use planning 

for the Monument. 

About 13 years ago, old mines presented safety and bat 

habitat issues for Chiricahua National Monument 

management. Today, however, there are no safety or bat 

habitat issues related to these old mines in the 

Monument (Alan Whalon, Chiricahua National 

Monument superintendent, personal communication, 

April 5, 2006). 

Mineral Specimen Collecting 

Mineral specimens are non-renewable resources that 

require park protection. Collecting, rockhounding, and 

gold panning of rocks, minerals, and paleontological 

specimens, for either recreational or educational 

purposes is generally prohibited in all units of the 

National Park System (36 C.F.R. § 2.1(a) and § 2.5(a)). 

Violators of this prohibition are subject to criminal 

penalties. 

Collecting rock specimens is an issue for park 

management. Visitors collect samples of galena and 

sphalerite (lead-zinc minerals) as well as spherulites 

along Monument trails. The marble-like spherulites, 

known as “hailstones,” weather out of volcanic tuff, 

especially along Hailstone Trail. The number of 
8 NPS Geologic Resources Division 

specimens removed from the Monument has not been 

documented, and it is unclear how large a problem 

mineral theft is for the Monument. Nevertheless, 

improving visitor education regarding the prohibition 

against collecting may help to reduce mineral theft. 

Subsurface Contamination/Decontamination 

Soil and groundwater were contaminated in 1994 when 

an underground storage tank leaked. The tank was 

pulled, and decontamination at the site is ongoing 

because the contaminant plume is difficult to define and 

mitigate (see Appendix B). 

Sewer and Septic Problems 

The septic system for Chiricahua National Monument is 

old and deteriorating, but issues associated with the 

system are related more to park finances than to geology 

(see Appendix B). Management of Monument finances is 

beyond the scope of this report. The septic system that 

serves the campground is often used to capacity 

(National Park Service 2001). Because Faraway Meadow 

is narrow and much of the area is within the floodplain, a 

good location for a new septic system is difficult to 

identify. Issues concerning the hydrology of Chiricahua 

National Monument may be addressed to the Water 

Resources Division of the National Park Service. 

Figure 4. The Visitor Center at Chiricahua National Monument lies within Faraway Meadows and is susceptible to flash flooding. 

Photograph courtesy of the National Park Service, http://www.nps.gov/chir/planyourvisit/hours.htm. 
CHIR Geologic Resource Inventory Report 9 

Figure 5. Surge deposits (white) and welded tuff deposits (brown) along Sugarloaf Mountain Trail pose a landslide hazard at Chiricahua 

National Monument. Photograph by John Graham (Colorado State University), April 5, 2006. 
10 NPS Geologic Resources Division 

Figure 6. Landslide potential. Erosion of the soft, ash-rich white layer at the base of the Upper Member of the Rhyolite Canyon Tuff 

causes undercutting of the more resistant welded tuff and subsequent cliff collapse. 
CHIR Geologic Resource Inventory Report 11 

Geologic Features and Processes 

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

in Chiricahua National Monument. 

Weathering, volcanic activity, and faulting combined to 

form the principal geologic features found within 

Chiricahua National Monument. The unusual pinnacles, 

columns, and balanced rocks owe their origin to 

differential weathering processes and are the reason for 

the Monument. Other equally outstanding geologic 

features resulted from volcanic episodes that impacted 

the southeastern Arizona area and from regional 

tectonics associated with the western margin of North 

America. 

Features Related to Differential Weathering and Erosion 

Hoodoos, Balanced Rocks, and Slot Canyons 

The pinnacles and balanced rocks, for which the 

Monument is best known, are exposed in what look like 

organ pipes about 0.8 km (0.5 mi) from the Visitor 

Center, along the main park road, and in the Heart of 

Rocks area (fig. 1) (Pallister and du Bray 1997; Pallister et 

al. 1997; Bezy 2001). The spires are particularly abundant 

in canyons on the west side of the Chiricahua Mountains 

(Chronic 1983). Few columns are present on the eastern 

slope due to the lack of vertical fractures in the rocks in 

that area. These hoodoos are erosional features that 

formed as the Rhyolite Canyon Tuff was dissected by 

water and wind (Pallister et al. 1997). Weathering along 

horizontal fractures in the welded tuff is responsible for 

the irregular profiles. 

Chemical and physical weathering processes are 

commonly concentrated along joints in the rock. In the 

volcanic rocks at Chiricahua National Monument, joints 

intersect one another at high angles to form rectangular 

blocks. Along Sugarloaf Mountain Trail, the average 

spacing between extensive ‘master’ joints is 4.3–5.5 m 

(14–18 ft) (Bezy 2001). Water from rain or snowmelt 

seeps into fractures. When the water freezes, the increase 

in volume exerts sufficient pressure to shatter rock 

through a process called ‘frost wedging.’ When the ice 

thaws, pieces of shattered rock that were held in place by 

the ice collapse and are washed away, thereby widening 

fractures. 

Plant roots also seek water in joints. Their continued 

growth exerts pressures that also lead to rock 

degradation along joints. The slightly acidic water can 

also cause chemical degradation of rock along joint walls. 

Over hundreds of thousands of years, weathering and 

erosion have widened and deepened crevices developed 

along joints, leading to the formation of rectilinear 

ridges, pinnacles, and slot canyons. 

The hoodoos are relict landforms from the Pleistocene 

ice ages (approximately 1.6 million to 10,000 years ago). 

Frost wedging during the wetter glacial climate sculpted 

the bedrock into angular columns. During the last 10,000 

years, the pinnacles have been smoothed to their present 

cylindrical and hourglass shapes by chemical weathering, 

repeated freezing and thawing, lichen attack, and other 

processes. Wind erosion helps shape the balanced rocks. 

Sand grains, blown by the wind, act like sandpaper or 

sand blasting to effectively round the corners of the 

columns. 

Slot canyons can be found along Echo Canyon Loop 

Trail. These canyons are commonly as much as 40 times 

deeper than they are wide. Cut into the rhyolite, they are 

almost exclusively controlled by rectilinear joint sets. 

These narrow canyons and the fin-like, pinnacle-lined 

walls that separate them are the result of repeated 

freezing and thawing and subsequent flushing away of 

rock fragments by running water. 

Natural Bridge 

A natural bridge with a 9-m (30 ft) span of welded tuff 

can be seen from the overlook at the end of the Natural 

Bridge Trail. The trailhead is located approximately 2 km 

(1.25 mi) from the Visitor Center along the Bonita 

Canyon scenic drive. The trail traverses the Middle 

Member of the Rhyolite Canyon Tuff and climbs to a 

high plateau where piñon pine and alligator juniper rise 

above a chaparral community of manzanita, bear grass, 

and yucca. High on the far wall of the canyon, the natural 

bridge crosses a narrow gulch lined by oak trees. 

Natural bridges differ from arches, such as those at 

Arches National Park in Utah, in that they are formed by 

flowing water. The natural bridge in Chiricahua National 

Monument probably formed during the wetter 

Pleistocene glacial period when flowing water eroded the 

weaker rock beneath the bridge. 

Case Hardening 

Case hardening is the process that has caused the 

surfaces of most of the pinnacles and cliffs in Chiricahua 

National Monument to develop a protective mineral 

rind. Ongoing water evaporation at the rock’s surface 

draws moisture from pore spaces within the rock. This 

water is re-precipitated on the surface and evaporates. As 

the water evaporates, it leaves behind, or deposits, a 

durable film of amorphous silica. The silica accumulates, 

hardens, and enhances rock strength, thereby protecting 

the surface from chemical weathering and low energy 

erosion. However, the rock beneath the surface becomes 

weaker than the case-hardened surface so that once the 

protective outer surface is broken, the softer, weathered 

zone is exposed to differential erosion and develops 

tafoni, which are commonly referred to as ‘stonepecker 

holes’ (Bezy 2001). 
12 NPS Geologic Resources Division 

Tafoni 

Tafoni are cavernous openings or pits that are common 

along joints, bedding planes, or other zones of weakness 

in the bedrock. These openings can range from the size 

of bottle caps up to several meters in diameter. The word 

comes from spectacular honeycomb structures that form 

in granite along the coast of Sicily. Tafoni are the result 

of several processes acting together. Differential erosion 

causes small depressions to form adjacent to surfaces 

hardened by mineral crusts. These openings enlarge as 

erosive agents attack the more porous interior rock 

adjacent to case-hardened zones. Resulting shaded 

cavities have higher humidity and lower temperatures 

than adjacent rock and experience continued differential 

erosion as a consequence, resulting in accelerated 

disintegration. 

Desert Varnish 

Desert varnish (also called ‘rock varnish’) consists of 

brown and black blotches on the buff-colored rock 

pinnacles in the Monument. Sandstone, basalt, and many 

metamorphic rocks have hard, erosion-resistant surfaces 

that promote the formation of rock varnish. Typically 

less than a quarter of a millimeter (a hundredth of an 

inch) thick, desert varnish is a coating formed by 

colonies of microscopic bacteria. The bacteria absorb 

trace amounts of manganese and iron from the 

atmosphere and precipitate the minerals as a black layer 

of manganese oxide or reddish iron oxide on the rock 

surface. The thin layer of desert varnish also includes 

clay particles that help shield the bacteria against 

desiccation, extreme heat, and intense solar radiation. 

Solution Pans 

Flat-bottomed solution pans form on many relatively 

horizontal surfaces, including the level tops of many 

hoodoos. These circular, dish-shaped depressions may 

reach 1 m (3 ft) in diameter and 10 cm (4 in) in depth and 

can hold water for weeks after rain or snowmelt (Bezy 

2001). Chemical and physical weathering processes, 

similar to those responsible for tafoni formation, attack 

the rock at points of weakness. An orange, iron-rich rock 

varnish coats the rims of many solution pans. The orange 

tint results from the oxidation (rust) of small quantities 

of iron (Bezy 2001). 

Horizontal Ribs 

Horizontal ribs appear as small-scale ridges exposed on 

the surface of rock pinnacles. The ribs and adjacent 

depressions vary from about 1 to 10 cm (0.5 to 4 in) in 

width and are as much as 20 cm (8 in) long. The 

depressions between the ribs are cavities formed by 

weathering of softer ash layers and fiamme (pumice 

blocks flattened and deflated during welding of rhyolite). 

The welded tuff composing the ribs is more resistant to 

weathering than the ash layers, and consequently forms 

positive features on the rock. 

Talus Cones 

Steep, triangular piles of rock rubble, known as talus 

cones, are common landforms in high mountains and 

deserts. Talus cones form from the accumulation of 

fallen, angular rock fragments dislodged by ice wedging, 

plant roots, chemical decomposition, and other 

weathering processes. 

In the Chiricahua Mountains, talus cones may be relict 

features produced during the cooler and wetter climate 

of the Pleistocene ice ages (1.6 million to 10,000 years 

ago) when freeze-thaw cycles were more frequent (Bezy 

2001). Talus rocks are encrusted with lichen and have 

been partially stabilized by vegetation, which indicates 

minor recent movement. Talus cones can be seen along 

the Hailstone segment of Echo Canyon Loop Trail. 

Most slope angles are near their upper limit (angle of 

repose) and can be very unstable. Climbing on the cones 

can trigger rockslides. 

Exfoliation Shingles 

Blocky features that resemble small, overlapping shingles 

cover the narrow necks of many pinnacles along Echo 

Canyon Loop Trail. Shingles extend only a few inches 

into the bedrock. Desert varnish coats the exfoliation 

shingles, which are case hardened. The origin of these 

weathering features is still unknown (Bezy 2001). 

Chicken Heads 

Knobby or plate-like protrusions called ‘chicken heads’ 

have developed on otherwise smooth rock surfaces near 

the base of many pinnacles. These features contain 

remnant coatings of rock varnish and lichen, have been 

case hardened, and are more resistant to weathering than 

the surrounding rock surfaces. Once the protective 

coating is worn away, the chicken heads weather to a 

smooth surface. 

Inverted Topography 

Inverted topography represents a large-scale geomorphic 

feature that formerly was a topographic low but 

presently is a topographic high that reflects the 

difference in erosion resistance between adjacent rock 

bodies. For example, the Rhyolite Canyon Tuff flowed 

into a valley when it erupted from the Turkey Creek 

caldera. However, over the past 26.9 million years, the 

welded tuff did not erode as quickly as the surrounding 

rocks. Now, because of its relative resistance to erosion, 

the Rhyolite Canyon Tuff stands above the surrounding 

terrain. 

Sugarloaf Mountain is another excellent example of 

inverted topography. The dacite that caps the mountain 

once filled a valley eroded into the Rhyolite Canyon 

Tuff. Dacite is more resistant to erosion than the tuff, so 

as erosion continued to degrade the tuff, the top of 

Sugarloaf became a prominent knob above the 

surrounding landscape. What was once a valley bottom is 

now a mountaintop. 

Lichens 

Lichen colonies are common features on rocks at 

Chiricahua National Monument. These colonies of algae 

and fungi weather rocks by both chemical and physical 

processes. Acids produced by lichens etch minerals such 

as feldspar and quartz. Lichens, attached firmly to rock 

surfaces, expand and shrink when they are wet and 
CHIR Geologic Resource Inventory Report 13 

dried, and in doing so, they exert enough pressure to 

dislodge mineral grains, chip off rock flakes, and enlarge 

cracks. The process is slow but relentless. Over time, the 

rock disintegrates grain-by-grain. 

Volcanic Features Related to the Turkey Creek Caldera 

Turkey Creek Caldera 

Visible on the southern skyline from the top of Sugarloaf 

Mountain, the highest peaks of the Chiricahua 

Mountains represent remnants of the Turkey Creek 

caldera. Magma, water vapor, carbon dioxide, and other 

gases accumulated in a massive magma chamber a few 

miles below the land surface and erupted explosively 

26.9 million years ago. More than 400 km3

 (100 mi3) of 

pumice and ash were blown into the atmosphere. The 

pyroclastic material blanketed more than 3,100 km2

(1,200 mi2

) and compacted to become the Rhyolite 

Canyon Tuff. The magma chamber collapsed following 

the explosion and formed the Turkey Creek caldera, a 

giant depression 19 km (12 mi) across and 1,500 m (5,000 

ft) deep (Pallister et al. 1997; Bezy 2001). Subsequent 

burial by additional pumice and ash, faulting, and 

erosion have obscured the circular form of the caldera. 

As mentioned in the Geologic Issues section, the volume 

of material from the Turkey Creek volcano was much 

greater than 19th and 20th century stratovolcano 

eruptions. In addition, the Turkey Creek eruption did 

not proceed from a central vent but from a series of vents 

that ruptured the land surface. Although larger than 

Krakatoa, Mount St. Helens, and Mount Pinatubo, the 

Turkey Creek eruption is not the biggest known. Similar 

types of eruptions in the San Juan Mountains of 

Colorado and in what is now Yellowstone National Park 

each vented more than 2,000 km3

 (500 mi3) of magma 

(Pallister et al. 1997). Still, the Turkey Creek caldera 

remains an excellent example of this style of volcanic 

eruption. 

Rhyolite Canyon Tuff 

When the Turkey Creek volcano erupted, the liberated 

gas produced both ash clouds and pyroclastic flows. The 

ash clouds consisted of billions of microscopic shards of 

volcanic glass, fragments of crystals, and microscopic 

rock fragments. Boiling clouds of very hot (> 540 °C 

[1,000°F]) ash, pumice, rock fragments and gas were 

blown into the atmosphere and propelled across the land 

surface at speeds of 80 to more than 160 km/hr (50 to 

more than 100 mi/hr) (Pallister et al. 1997). The intense 

heat scoured everything in its path. Pyroclastic flows 

developed as the ash clouds lost gas and deflated. The 

pyroclastic flows ponded in valleys to form thick 

deposits of steaming ash and pumice. A ‘tuff’ is a volcanic 

rock composed primarily of ash and pumice, and if the 

shards of volcanic glass and the pumice fragments are 

still hot when deposited, they fuse together and compact 

under their own weight to form a rock called ‘welded 

tuff.’ 

Before the Turkey Creek eruption, the Chiricahua 

National Monument area was a valley. Pyroclastic flows 

from the caldera-forming eruption filled the valley to a 

depth of at least 490 m (1,600 ft) (Pallister et al. 1997). 

The deposit was named the Rhyolite Canyon Tuff for the 

excellent exposures in Rhyolite Canyon. Primary 

components of the tuff include pumice, ash, rock 

fragments, and crystals of feldspar and quartz. Most of 

the Rhyolite Canyon Tuff is densely welded, but some 

layers of poorly welded ash and pumice and surge beds 

of ash form horizontal white bands within the unit. 

The white, poorly welded layers are visible in the cliffs of 

the Monument and mark contacts between distinct 

sequences of pyroclastic flows (fig. 5). In Chiricahua 

National Monument, two such contacts divide the 

Rhyolite Canyon Tuff into three members. Contacts 

between each member are defined by white, ash-rich 

surge beds formed from material that was blasted from 

the volcano at high velocity. The surge beds are poorly 

welded relative to the densely welded pyroclastic flows 

that subsequently buried them. 

The three members of the Rhyolite Canyon Tuff 

represent three giant eruptions that occurred in rapid 

succession and that dwarf historic eruptions (Pallister et 

al. 1997; Kiver and Harris 1999). The Middle Member 

alone is a startling 268 m (880 ft) thick. Each member 

consists of densely welded pyroclastic flows composed 

of pumice, ash, rock fragments, and crystals of feldspar 

and quartz. 

Welded Tuff and Fiamme 

Both the welded tuff and the unwelded tuff layers in the 

Rhyolite Canyon Tuff are well preserved along Sugarloaf 

Mountain Trail. White streaks in the rock are flattened 

pumice fragments, called ‘fiamme.’ Pumice, a soft 

volcanic material permeated by formerly gas-bubblefilled cavities was compressed, while still hot, and the 

bubbles were deflated by the weight of overlying volcanic 

ash. Volcanic rock that encloses fiamme is composed of 

microscopic pieces of volcanic glass and crystal 

fragments. 

Surge Beds, Liesegang Bands, and Fumarole Pipes 

The only location in the Chiricahua Mountains where 

the contact between the Upper Member and the Middle 

Member of the Rhyolite Canyon Tuff is exposed is along 

Sugarloaf Mountain Trail (fig. 5). White, ash-rich surge 

beds at the base of the Upper Member mark the dynamic 

contact between these pyroclastic flows and the ash-fall 

layers of the Middle Member. 

Surge beds are a type of pyroclastic flow deposit that 

record lateral explosions that blasted ash from the 

volcano at high velocity. As gases escaped from the 

violent explosions that propelled ash clouds down the 

slopes of the Turkey Creek caldera, a frothy ash cloud, 

flowed, or surged, from the volcano and settled in 

topographically low areas. The surge beds intersect one 

another at low angles, producing cross-bedding. In some 

places, coarser grained beds overlie finer grained beds to 

form a feature called ‘inverse graded bedding.’ 

Volcanic ash subsequently settled on top of the 

pyroclastic flows and fused into thick layers of welded 

tuff. The soft, ash-rich, white- to- light gray surge layers 
14 NPS Geologic Resources Division 

contribute to mass wasting along Sugarloaf Mountain 

Trail (fig. 6) (Pallister et al. 1997; Bezy 2001). 

Secondary chemical processes produced features called 

‘Liesegang bands’ in the surge beds along Sugarloaf 

Mountain Trail. These bands formed when water in the 

ash boiled and precipitated less-soluble minerals 

(Pallister et al. 1997; Bezy 2001). They can be found at the 

base of some preserved fumarole pipes and within the 

surge deposits (fig. 7). 

When water in the ash boiled, the resulting steam blasted 

to the surface through the overlying ash-flow tuff to form 

irregular vertical conduits. These features, called 

‘fumarole pipes,’ are preserved in the ash and the 

overlying welded tuff along Sugarloaf Mountain Trail 

(fig. 8) (Pallister et al. 1997; Bezy 2001). Fine-grained ash 

was blown out of the fumarole pipe, leaving behind 

coarser ash and crystals in the pipe-like conduit. The 

preserved fumarole pipes suggest that the top of the 

Middle Member of the Rhyolite Canyon Tuff and/or the 

overlying basal white ash were wet prior to deposition of 

the hot ash of the Upper Member (Pallister and du Bray 

1997). 

Moat Deposits and Flow Ramps 

Following the eruption of the Rhyolite Canyon Tuff, the 

central part of the caldera depression was uplifted south 

of the Monument, forming a feature known as a 

resurgent dome. A circular valley, or moat, formed 

between the resurgent dome and the edge of the caldera 

depression. Highly viscous rhyolite lava leaked into the 

moat, piled up on itself, and solidified into vertical 

features called ‘flow ramps.’ Visible from the lookout 

atop Sugarloaf Mountain, moat lava rock forms the eastwest ridgeline south of Pinery Canyon and extends to the 

south along the crest of the Chiricahua Mountains. The 

hillside above and just south of Downings Pass on the 

Methodist Camp road, a side road south of the Pinery 

Canyon road between the Monument and Portal, 

Arizona, contains an excellent exposure of flow-ramped 

moat lava (Pallister et al. 1997). 

Columnar Joints 

Columnar-jointed rocks that have not weathered to 

hoodoos form cliffs of Rhyolite Canyon Tuff north of 

Picket Canyon. The columns are parallel cracks that 

formed as the volcanic ash beds cooled and contracted. 

These contraction joints form at right angles to cooling 

surfaces of lava flows or tuffs. The intersection of the 

joint sets form rock columns, or ‘columnar joints.’ 

Columnar joints are also well developed at Devils 

Postpile National Monument in California. 

Dacite Caprock 

Sugarloaf Mountain is capped by a dacite lava flow that 

weathers to form a blocky, rubbly surface. Dacite 

contains about 63-70% silica compared to rhyolite, 

which contains about 77% silica. Magma of this 

composition resided in the lower part of the magma 

chamber and was erupted after the Rhyolite Canyon 

Tuff. It did not erupt as violently as the rhyolite because 

it contained less water and volatiles. Most of the dacite 

lava flowed into the caldera depression although some of 

the lava flowed out of the caldera and down the former 

valley into the area of the Monument. The dacite 

contains large crystals of feldspar. A rock in which large 

crystals are surrounded by fine-grained groundmass, 

such as this dacite, is called a ‘porphyry’ and the large 

crystals are called ‘phenocrysts.’ 

Igneous Dikes 

Not all of the magma was extruded onto the surface. 

Rhyolite magma that intruded into pre-Turkey Creek 

caldera rocks and formed tabular features called ‘igneous 

dikes.’ Igneous dikes form discordant to the bedding or 

layering of the rocks they intrude. The igneous dike near 

the King of Lead Mine is visible from Sugarloaf 

Mountain Trail. This dike and others like it stand out 

from the surrounding topography because they are more 

resistant to weathering than the rocks that they intruded. 

Spherulites 

Rounded spherulites, found along Hailstone Trail, 

formed as volcanic ash cooled and began to crystallize. 

The spheroidal, marble-like shape resulted from radial 

growth of secondary needle-shaped crystals of quartz 

and feldspar around a common center. At one time, they 

were thought to be volcanic hailstones formed by 

repeated accumulation of concentric ash layers around 

water droplets or crystals rising and falling through 

volcanic ash clouds (Chronic 1983; Kiver and Harris 

1999). However, the pellets along Hailstone Trail contain 

radiating crystals, lack concentric layering, and except 

for being harder, are similar in composition to the 

surrounding tuff. Evidence suggests an origin following 

deposition of the tuff (Pallister and du Bray 1997; Bezy 

2001). 

Features that Predate the Turkey Creek Caldera 

Volcanic Features 

The hills north and south of Faraway Ranch consist of 

rhyolite formed from lava in that pooled around 

eruption vents prior to the Turkey Creek caldera 

eruptions. Rhyolite of Erickson Ridge, a unit in the 

Faraway Ranch Formation, contains phenocrysts of 

plagioclase and biotite. Dark colored andesite and basalt, 

which form from magma low in silica, are exposed in 

road cuts uphill from Bonita Park on the road to 

Sugarloaf Mountain and Massai Point (Pallister et al. 

1997). 

A vertical flow ramp in Faraway Ranch Formation 

rhyolite lava is exposed in the cliff north of the Faraway 

Ranch parking lot (Pallister et al. 1997; Pallister and du 

Bray 1997). Thin beds of rhyolite ash and rock debris in 

the Faraway Ranch Formation represent small 

explosions that accompanied the eruption of rhyolite 

lava and produced swiftly flowing, turbulent gaseous 

clouds of pyroclastic material called ‘nuée ardente’ 

(glowing cloud and avalanche) deposits. 

Sedimentary Features 

The Tertiary-age, red-weathering beds of sandstone and 

conglomerate of Bonita Park underlie the Faraway 

Ranch Formation (fig. 3). These sedimentary rocks 
CHIR Geologic Resource Inventory Report 15 

represent stream deposits laid down along the floor of 

the ancient Monument valley about 30 million years ago 

(Pallister et al. 1997). 

Features in the Lower Permian limestones in the 

northeastern section of the Monument provide evidence 

of a time when marine environments transgressed into 

southeastern Arizona. Productid brachiopods 

(brachiopods with long spines to attach to the substrate), 

echinoids (related to modern sea urchins and sand 

dollars), and other marine invertebrates inhabited 

offshore, well-oxygenated marine environments. Tweet 

et al. (2008) summarized the paleontological resources 

(fossils)of Chiricahua National Monument and the other 

parks of the Sonoran Desert Inventory and Monitoring 

Network. 

Structural Features 

During the Miocene (20-15 million years ago), rising heat 

from the mantle began to thin the crust beneath the 

southwestern United States, causing the crust to bulge 

upward. The crust began to stretch or pull apart, and as it 

stretched, steeply-dipping normal faults developed to 

accommodate the extension. Uplifted blocks of crust 

called ‘horsts’ (German for ‘heap’) developed into 

today’s fault-bounded, north-south trending mountain 

ranges. Downdropped blocks filled with sediment to 

form relatively flat, fault-bounded valleys, or ‘grabens’ 

(German for ‘ditch’). San Simon Valley to the east and 

parts of Sulphur Springs Valley to the west are normalfault-bounded grabens. 

At the eastern boundary of Chiricahua National 

Monument, where the paved road to Sugarloaf 

Mountain and Massai Point turns south after ascending 

Bonita Canyon, the steep-sided Whitetail Valley is 

parallel to a fault zone across which distinct rock masses 

have been juxtaposed (Pallister et al. 1997). The most 

recent movement along the fault dropped the block east 

of the fault down relative to the rocks west of the fault, 

forming Whitetail Valley; these fault displacements 

dragged and folded the Rhyolite Canyon Tuff down into 

the valley. Formerly horizontal welded- pumice fiamme 

are now steeply tilted into the valley. 
16 NPS Geologic Resources Division 

Figure 7. The “boiling pot” at the base of a fumarole pipe (arrow). Concentric layers are Liesegang bands. The light-gray layers below the 

fumarole pipe are surge beds, which were deposited from horizontally directed explosive blasts of ash, crystals, and rock debris. Liesegang 

bands also overprint these layers. Photograph by John Graham (Colorado State University), April 5, 2006. 
CHIR Geologic Resource Inventory Report 17 

Figure 8. A fumarole pipe preserved in the Rhyolite Canyon Tuff, Sugarloaf Mountain Trail. Photograph by John Graham (Colorado State 

University), April 5, 2006. 
18 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 Chiricahua National Monument. The accompanying 

table is highly generalized and 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 Chiricahua 

National Monument informed the “Geologic History,” 

“Geologic Features and Processes,” and “Geologic 

Issues” sections of this report. Geologic maps are 

essentially two-dimensional representations of complex 

three-dimensional relationships. The various colors on 

geologic maps illustrate 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 to 

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 do 

not show soil types and are not soil maps, 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. Geologic 

maps do not show where the next landslide, rockfall, or 

volcanic eruption will occur, but mapped deposits show 

areas that have been susceptible to such geologic 

hazards. Geologic maps do not show archaeological or 

cultural resources, but past peoples may have inhabited 

or been influenced by various geomorphic features that 

are shown on geologic maps. For example, alluvial 

terraces may preserve artifacts, 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. 9) for the age 

associated with each time period. This table highlights 

characteristics of map units such as susceptibility to 

hazards; the occurrence of fossils, cultural resources, 

mineral resources, and caves; and the suitability as 

habitat or for recreational use. 

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 map for Chiricahua National Monument: 

Pallister, J. S., and E. A. du Bray. 1997. Interpretive map 

and guide to the volcanic geology of Chiricahua National 

Monument and vicinity, Cochise County, Arizona. Scale 

1:24,000. Miscellaneous Investigations Series Map I2541. 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 shapefile and coverage 

GIS formats, 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 with appropriate symbology. GRI 

digital geologic data are included on the attached CD and 

are available through the NPS Data Store 

(http://science.nature.nps.gov/nrdata/). 
CHIR Geologic Resource Inventory Report 23 

Geologic History 

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

geologic map of Chiricahua National Monument, the environment in which those units 

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

Paleozoic rocks about 280 million years old are the oldest 

rocks exposed in Chiricahua National Monument 

(Pallister and du Bray 1997). However, the oldest rock in 

southeastern Arizona is the Pinal Schist that formed 

about 1.7 billion years ago during Precambrian time (fig. 

9). This metamorphic rock is exposed in the Dos Cabezas 

Mountains, between Chiricahua National Monument 

and Willcox, Arizona. At the time of its deposition, the 

Southwest may have looked like today’s western Pacific, 

where numerous volcanic belts are separated by seas 

(Hoffman 1989; Pallister et al. 1997). 

During Precambrian time, the southwestern coastline of 

North America paralleled the present border of 

Wyoming and Colorado. A sequence of volcanic belts, or 

island arcs, were plastered, or accreted, onto the margin 

of North America in a process of continental growth that 

is part of the global process of plate tectonics. By 1.4 

billion years ago, most of what is now the Arizona land 

surface had been added to the North American 

continent, forming a new coastal province. 

New masses of molten rock then intruded the accreted 

coastal province. The granodiorite in Fort Bowie 

National Historic Site, for example, intruded the Pinal 

Schist about 1.375 billion years ago (Drewes 1981). 

Another example of these Precambrian granitic 

intrusions can be found in nearby road cuts on Arizona 

highway 181, about 2.4 km (1.5 mi) east of Dos Cabezas, 

Arizona (Pallister et al. 1997). This granite contains 

feldspar crystals 2.54 cm (1 in) or more across. 

The next 800 million years of the geologic history of 

southeastern Arizona are a mystery. Erosion has 

removed any rocks that were deposited during this time, 

leaving an unconformity in the geologic record that 

separates the 1.4-billion-year-old Precambrian rocks 

from the 510–542-million-year-old Cambrian rocks (fig. 

9). This remarkable unconformity is exposed in road cuts 

5.6 km (3.5 mi) east of Dos Cabezas (Pallister et al. 1997). 

Paleozoic History 

Throughout the Paleozoic (542–251 million years ago), 

southeastern Arizona was covered by an ancient sea. 

Thick layers of carbonate and siliceous sediments 

accumulated on the sea floor. 

Ranging in age from 299 to 265 million years old, 

Permian-aged strata on the rugged flank of Timber 

Mountain are the only Paleozoic rocks exposed in 

Chiricahua National Monument. Fossil brachiopods, 

echinoid spines, and gastropods are abundant in the 

Concha Limestone, Colina Limestone, Epitaph 

Dolomite, Earp Formation, and Horquilla Limestone 

(fig. 3). These Permian strata record shallow-water coral 

reef environments (fig. 10) (Pallister et al. 1997). Also in 

the Permian, a shallow marine embayment encroached 

into southeastern New Mexico from the south. This 

embayment produced the Permian reef complex, 

exposed today in Guadalupe National Park and Carlsbad 

Caverns National Park. 

During the Permian (about 275 million years ago), what 

is now Wyoming and eastern Utah was located near the 

equator along the western margin of Pangaea (Biek et al. 

2000; Morris et al. 2000). Pangaea was the 

supercontinent that formed during the late Paleozoic as 

the globe’s landmasses sutured together. A dry, high 

atmospheric pressure climatic belt prevailed in this 

western part of Pangaea and resulted in restricted marine 

evaporitic conditions (Peterson 1980). Warm, shallow 

seas and sabkhas (broad, very flat surfaces near sea level) 

covered the area. 

At the close of the Permian, continental shelf and slope 

rocks were compressed against the western continental 

margin in the vicinity of what is now Nevada. Southeast 

of Arizona, the South American tectonic plate collided 

with the North American plate and closed the proto-Gulf 

of Mexico. The collision caused the uplift of the 

northwest-southeast-trending Ancestral Rocky 

Mountains in Colorado, the northeast-southwesttrending Sedona Arch in central Arizona, and the 

Mogollon Rim, an uplift in east-central Arizona. South of 

the Mogollon Rim, an offshore carbonate shelf 

developed in southeastern Arizona (Blakey 1980; 

Peterson 1980). 

The close of the Permian brought the third, and most 

severe, major mass extinction of geologic time. This 

extinction marked the end of the Paleozoic Era. Much 

more extensive than the extinction event that terminated 

the dinosaurs at the end of the Mesozoic, the end of the 

Permian extinction eliminated approximately 96% of all 

species (Raup 1991). There are a number of hypotheses 

regarding the processes that could cause such an 

extinction. One recent extinction hypothesis suggests 

that a comet, about 6–13 km (4–8 mi) in diameter, 

slammed into Earth (Becker et al. 2001). Such an impact 

could have triggered vast volcanic eruptions that spread 

lava over an area two-thirds the size of the United States. 

Powerful updrafts would have carried dust and grit 

swirling into the upper atmosphere. Particulate matter 

would have reflected and scattered sunlight, resulting in 

years of global cooling with freezing temperatures even 

during summertime. A recent example of this type of 

global cooling occurred in 1816, called “the year without 

a summer,” following an 1815 volcanic explosion in 

Tambora, Indonesia. Sulfuric emissions from the 
24 NPS Geologic Resources Division 

eruptions would have mixed with atmospheric water to 

produce downpours of corrosive acid rain. During the 

end of the Permian extinction, thousands of species of 

insects, reptiles, and amphibians died on land while in 

the oceans, coral formations vanished, as did snails, 

urchins, sea lilies, some fish, and the once-prolific 

trilobites. Five million years later, at the dawn of the 

Mesozoic Era, the oceans began to evolve into the 

chemistry of the modern oceans, and on land, the first 

mammals and dinosaurs emerged. 

Mesozoic History 

The next 150–180 million years of local geologic history 

is not represented in Chiricahua National Monument. 

The Permian Concha Limestone (about 280 million years 

old) is overlain by conglomerate and sandstone of the 

Cretaceous Bisbee Group (about 100 million years old) 

(fig. 11). The unconformity represents a period of uplift 

and erosion in southeastern Arizona. 

From middle Paleozoic through Mesozoic time, the 

western margin of North America was an active plate 

margin where dense oceanic crust was subducted 

beneath lighter continental crust. In plate tectonic 

theory, spreading ocean ridges and subduction zones act 

as “conveyer belts” that move lithospheric plates around 

the globe. As plates collide, sediments deposited in the 

trench that forms at the juncture of the two plates, as well 

as bits of oceanic crust (including islands like Hawaii and 

island arcs like Japan), are scraped off the top of the 

“conveyor belt” and accreted onto the edge of the 

continent, thereby contributing to continental growth. 

As oceanic crust sinks beneath continental crust, 

overlying rocks melt and begin to rise through the crust, 

becoming enriched in volatiles and melting some 

continental rocks. Magma may ascend directly to the 

surface and erupt as a volcano, or it may pond beneath 

the surface to form subterranean reservoirs of molten 

rock, known as magma chambers. Magma in these 

reservoirs cools slowly and eventually forms coarsegrained igneous rocks such as granite. 

During much of the Mesozoic Era, subduction zones 

underlay southeastern Arizona (Pallister et al. 1997). 

Volcanoes are common above subduction zones, and 

during the Mesozoic Era a volcanic island arc, similar to 

those that formed in the Precambrian and Paleozoic, 

formed off the coast of western North America. Magma 

chambers developed, forming island arc volcanoes and 

the Sierra Nevada batholith (including the granitic 

masses in Yosemite National Park) in California. About 

165 million years ago, huge volcanic eruptions in 

southeastern Arizona formed calderas in the Huachuca 

and southern Dragoon Mountains. 

During the Early Cretaceous in southern Arizona, the 

tectonic regime was dominated by rifting along the 

northwest-southeast-trending Bisbee Basin, which was 

located near the southwestern margin of the North 

American tectonic plate (fig. 11) (Elder and Kirkland 

1994; Dickinson and Lawton 2001; Haenggi and 

Muehlberger 2005). Rather than accreting land to the 

continent in this region, tectonic forces were pulling the 

land apart. Rifting associated with the Mojave-Sonora 

megashear, a strike-slip fault with horizontal 

displacement measured in tens to hundreds of 

kilometers, tilted the Mogollon slope towards the 

northeast and opened a series of local pull-apart basins 

(Elder and Kirkland 1994; Anderson and Nourse 2005). 

The Glance Conglomerate, the basal unit of the Bisbee 

Group in this area, represents proximal deposits of 

alluvial fan systems that rimmed local fault-block 

mountain ranges and basins (Bilodeau and Lindberg 

1983). Conglomerate beds in the Bisbee Group, which 

are widely exposed in the hills east of Whitetail Pass, 

contain cobbles of fossil-rich limestone shed from 

uplifted mountains composed of the underlying 

Paleozoic rocks. Fine-grained sedimentary rocks and 

lava flows overlie the conglomerate beds. Some 

sandstone beds contain petrified wood from fossilized 

trees while other beds are colored dark green or gray 

from abundant volcanic fragments. Lava that flowed into 

water formed pillow-like shapes (“pillow lava”) that can 

be seen along the road across Onion Saddle, between 

Chiricahua National Monument and Portal, Arizona. 

The Bisbee Group rocks record deposition in a shallow 

inland sea that extended from southeastern Arizona 

across southern New Mexico and to the Gulf of Mexico 

(fig. 11) (Pallister et al. 1997). 

During the Late Cretaceous, southeastern Arizona 

formed part of the western border of the most extensive 

interior seaway ever recorded in North America (fig. 12). 

As mountains rose in the west, the Gulf of Mexico 

continued to rift open in the south, and seawater 

encroached northward into an elongate depression 

forming in the western interior of North America. 

Marine water also began to transgress southward from 

the Arctic region. The seas advanced and retreated many 

times during the Cretaceous until a seaway extended 

from today’s Gulf of Mexico to the Arctic Ocean, a 

distance of about 5,000 km (3,000 mi) (Kauffman 1977). 

At the close of the Mesozoic Era, about 65 million years 

ago, another burst of volcanic activity and faulting in 

southeastern Arizona resulted from the Laramide 

orogeny (about 75–35 million years ago), an episode of 

tectonic compression and mountain-building that is 

responsible for the modern Rocky Mountains and most 

of the ores of copper, silver, and gold deposited in the 

southwestern United States (Pallister et al. 1997). Welded 

tuff that forms the summit of the Dos Cabezas 

Mountains erupted during this period, also. 

Cenozoic History 

Volcanism continued during the first half to two-thirds 

of the Tertiary because a subduction zone was present 

beneath the southwestern United States (fig. 13). The 

Santa Catalina Mountains of southern Arizona contain at 

least 12 plutons that can be divided into three intrusive 

epochs: (1) 70-65 million years ago (Latest Cretaceous to 

Paleocene), (2) 50-44 million years ago (Eocene), and (3) 

29-25 million years ago (Oligocene) (Anderson 1988). In 

the Chiricahua Mountains, most of the volcanic activity 

occurred between about 35 and 25 million years ago, 

primarily in the Oligocene epoch (fig. 13). 
CHIR Geologic Resource Inventory Report 25 

Dark andesitic and basaltic lava flows, exposed in the 

road cuts uphill from Bonita Park on the road to 

Sugarloaf Mountain and Massai Point, erupted from 

scattered volcanoes. Viscous rhyolite flows erupted from 

small volcanoes and were accompanied by nuée ardente 

(glowing cloud and avalanche) deposits consisting of thin 

beds of rhyolite ash and rock debris. Viscous rhyolite 

accumulated to form vertical flow ramps. Sedimentary 

rocks near Bonita Park were deposited by streams along 

the floor of the ancient Chiricahua National Monument 

valley about 30 million years ago (Pallister et al. 1997). 

About 32–28 million years ago, an assemblage of rhyolite, 

dacite, and andesite lavas and pyroclastic rocks were 

erupted into the area of Chiricahua National Monument. 

These became the Faraway Ranch Formation and 

underlie the Jesse James Canyon Tuff and Rhyolite 

Canyon Tuff in the Monument area (Pallister et al. 1997). 

This formation also includes the ash-rich deposits of the 

rhyolite on Erickson Ridge. 

As much as 240 m (790 ft) of rhyolite ash-flow tuff (the 

Jesse James Canyon Tuff) was deposited in an ancient 

valley in Chiricahua National Monument shortly before 

the Rhyolite Canyon Tuff was erupted. Since their 

compositions are similar, the Jesse James Canyon Tuff 

can be difficult to distinguish from the Rhyolite Canyon 

Tuff. 

As described in the Features and Processes section, the 

eruption that produced the Turkey Creek caldera 

occurred about 26.9 Ma. More than 400 km3

 (100 mi3) of 

magma was erupted from vents above the extensive pool 

of rhyolite magma and buried a region of at least 

3,100 km2

 (1,200 mi2) under a thick blanket of ash and 

pumice. The roof of the magma chamber collapsed, 

producing the Turkey Creek caldera (Pallister et al. 

1997). 

During the caldera-forming eruption, pyroclastic flows 

filled valleys adjacent to the volcano, including the valley 

where Chiricahua National Monument is today. Because 

of its dense welding and great thickness, this valley-filling 

deposit has not completely eroded away during the past 

26.9 million years. After millions of years, at least 490 m 

(1,600 ft) of pyroclastic flows still remain in the 

Monument. 

The dacite lava atop Sugarloaf Mountain records the 

final chapter in the volcanic history of Chiricahua 

National Monument. The source of this flow was about 

10 km (6 mi) southeast of Sugarloaf Mountain. 

Although the dacite atop Sugarloaf Mountain is the 

youngest volcanic rock in Chiricahua National 

Monument, caldera development continued in the area 

south of the Monument, where the central part of the 

caldera depression was uplifted to form a resurgent 

dome. Rhyolite lavas leaked out to fill the moat 

surrounding the dome. 

Faulting and erosion have dramatically changed the 

topography of the Chiricahua Mountains over the past 

27 million years. About 20 million years ago, subduction 

off the southwestern coast of North America ceased as 

the former East Pacific Ocean spreading ridge ran into 

the subduction zone (Pallister et al. 1997; Kiver and 

Harris 1999). Plate motion shifted to strike-slip faulting, 

initiating the San Andreas Fault system of California. 

When subduction ceased, volcanism waned in the 

Chiricahua region. Strike-slip faulting and high heat flow 

beneath the southwestern region of the United States 

combined to cause the crust to stretch, or pull apart. 

Large crustal blocks were downdropped along highangle normal faults, creating grabens, while other blocks 

were uplifted into mountain ranges, known as horsts. 

This type of regional faulting produced the Basin and 

Range Province of today’s southwestern landscape. 

Nearly vertical normal faults separate the Chiricahua 

Mountains from the San Simon Valley to the east and 

parts of the Sulphur Springs Valley to the west (Pallister 

et al. 1997). In some areas, such as in the Pinaleno and 

Rincon–Santa Catalina Mountains, low-angle faulting 

also accommodated crustal extension. During this 

extension process, small amounts of basalt magma leaked 

from the underlying mantle to form the San Bernadino 

volcanic field along the southeastern flank of the 

Chiricahua Mountains. 

Downward-cutting streams, faulting, and erosion 

exposed the rocks in the Chiricahua Mountains as uplift 

of southeastern Arizona continued into the Quaternary. 

Sediments flushed from the canyons during flash floods 

have formed alluvial fans along the mountain fronts and 

continue to fill the basins adjacent to the mountain 

ranges. Focused along joint planes, wind and water 

erosion proceeded to dissect the welded tuff into the 

extraordinary pinnacles and columns characteristic of 

Chiricahua National Monument today. 
26 NPS Geologic Resources Division 

Figure 9. Geologic Timescale. Adapted from the U.S. Geological Survey (http://pubs.usgs.gov/fs/2007/3015/). Red lines indicate major 

unconformities between eras. Included are major events in the history of life on Earth and tectonic events occurring on the North American 

continent. Absolute ages shown are in millions of years (Ma). Compass directions in parentheses indicate the regional location of individual 

geologic events.
CHIR Geologic Resource Inventory Report 27 

Figure 10. Early Permian paleogeographic map of the southwestern United States. About 270 million years ago, a shallow sea encroached 

into southeastern Arizona. The yellow star is the approximate location of today’s Chiricahua National Monument. Browns and yellows 

denote land, light blue represents shallow marine, and dark blue represents deeper marine environments. The arrow in the lower left corner 

of the map shows the relative direction of movement of the offshore land masses relative to the North American margin. The “transform 

fault” marks the suture zone between the oceanic plate and the North American plate, although Permian plate boundaries are not well 

defined. The “Cordilleran (Wasatch) hingeline” marks the location of the future Wasatch Mountains. Map modified from Dr. Ron Blakey 

(Northern Arizona University), http://jan.ucc.nau.edu/~rcb7/perpaleo.html, accessed February 2007. 
28 NPS Geologic Resources Division 

Figure 11. Early Cretaceous paleogeographic map of the southwestern United States. The yellow star is the approximate location of today’s 

Chiricahua National Monument. About 130 million years ago, the shallow marine Bisbee Basin in southeastern Arizona was the site of 

tectonic rifting in which lithospheric plates are in the process of splitting apart. An epicontinental seaway encroached from the north. The 

“transtensional basin,” “accretionary prism mélange,” “fore arc basin,” and “fore-arc subduction complex” are associated with the oceaniccontinental (Andean-style) subduction zone between the North American Plate and the Farallon Plate. The thick, black line marks the 

approximate location of the subduction zone. Basins in southern Arizona and California formed due to strike-slip, extensional faulting 

(dashed lines) and were the sites of thick marine and continental deposition. Map modified from Dr. Ron Blakey (Northern Arizona 

University), http://jan.ucc.nau.edu/~rcb7/crepaleo.html, accessed March 2007. 
CHIR Geologic Resource Inventory Report 29 

A) Western Interior Seaway of North America (light blue) 

B) Depositional patterns in the southwestern United States during the Late Cretaceous 

Figure 12. Late Cretaceous paleogeographic map of North America. (A) About 80 million years ago, an inland seaway (light blue) extended 

from the Gulf of Mexico to the Arctic Ocean. Map courtesy of Dr. Ron Blakey (Northern Arizona University), 

http://jan.ucc.nau.edu/rcb7/namK85.jpg. (B) Vast alluvial plains formed in the southwest as the seaway slowly retreated to the northeast 

about 75 million years ago. The yellow star is the approximate location of today’s Chiricahua National Monument. Mountains rose from 

compression of the Cordilleran arc along the western margin of North America, marked by the thick, dashed lines. Transform faults, caused 

by oblique collision with the Farallon Plate, transported pieces of the western margin northward along the edge of North America. Map 

modified from Dr. Ron Blakey (Northern Arizona University), http://jan.ucc.nau.edu/rcb7/crepaleo.html, accessed February 2009. . 
30 NPS Geologic Resources Division 

Figure 13. Oligocene paleogeographic map of the southwestern United States. About 30-35 million years ago, volcanism was widespread 

across much of the Western Interior of North America. The first stages of the Rio Grande Rift in New Mexico and southern Colorado 

developed as parts of western North America changed from compressional tectonics to extensional tectonics. The East Pacific Rise (orange 

line), a Pacific spreading center, neared the coast of southwestern North America. Its impending collision would cause subduction to cease 

and initiate strike-slip faulting and the San Andreas Fault system. The arrows in the lower left corner show the direction of movement along 

the Medocino transform fault (green line), which separated the Pacific Plate (south of the fault) from the Farallon Plate (north of the fault). 

The thick, black line represents the boundary between the North American Plate and the Farallon Plate. The yellow star is the approximate 

location of today’s Chiricahua National Monument. Map modified from Dr. Ron Blakey (Northern Arizona University), 

http://jan.ucc.nau.edu/~rcb7/terpaleo.html, accessed February 2009. 
CHIR Geologic Resource Inventory Report 31 

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://wrgis.wr.usgs.gov/docs/parks/misc/glossarya.html. 

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

or event in years; commonly refers to ages determined 

radiometrically. 

accreted. The process by which continental crust grows 

thorugh the addition of smaller fragments of crust to 

its margins. 

alluvial fan. A fan-shaped deposit of sediment that 

accumulates where a high-gradient stream flows out of 

a mountain front into an area of lesser gradient. 

alluvium. Stream-deposited sediment that is generally 

rounded, sorted, and stratified. 

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

which is filled with minerals. 

andesite. A volcanic rock with about 52–63% silica. 

anhedral. A grain lacking well-developed crystal faces. 

aphanitic. Fine-grained igneous rock whose components 

are not distinguishable with the unaided eye. 

ash (volcanic). Fine pyroclastic material ejected from a 

volcano (also see tuff). 

ash flow. A dense cloud composed predominantly of hot 

ash and pumice. Moves rapidly due to liberation of gas 

from pumice and to ingestion of air at flow front. A 

type of pyroclastic flow. 

asthenosphere. Weak layer in the upper mantle below 

the lithosphere where seismic waves are attenuated. 

basalt. A dark-colored volcanic rock low in silica 

(<52%). 

basement. The undifferentiated rocks, commonly 

igneous and metamorphic, that underlie the rocks at 

the surface. 

basin (sedimentary). Any depression, from continental 

to local scales, into which sediments are deposited. 

basin (structural). A regional depression bounded on at 

least one side by a fault zone. 

batholith. A massive, discordant pluton, greater than 100 

km2 (40 mi2), and often formed from multiple 

intrusions. 

bed. The smallest lithostratigraphic unit, distinguishable 

from beds above and below, and commonly ranging in 

thickness from 1 cm (0.4 in) to 1–2 m (3–6 ft). 

bedding. Depositional layering or stratification of 

sediments. 

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

breccia. A coarse-grained, generally unsorted, 

sedimentary rock with cemented angular clasts. 

calcilutite. A limestone consisting predominantly (>50%) 

of detrital calcite particles of silt and/or clay size; a 

consolidated carbonate mud. 

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

summit of a volcano formed by explosion or collapse. 

celadonite. A soft, green or gray–green, earthy, 

dioctahedral mineral of the mica group. 

chatoyant. The property of some minerals to produce a 

distinct reflected color or luster. The feldspar mineral 

sanidine in the Rhyolite Canyon Tuff shows this 

property. 

cementation. The process by which clastic sediments are 

converted into rock by precipitation of mineral cement 

among the grains of the sediment. 

chemical weathering. Chemical breakdown of minerals 

at Earth’s surface via reaction with water, air, or 

dissolved substances; commonly results in a change in 

chemical composition more stable in the current 

environment. 

chicken head. Knobby or plate-like protrusions that are 

case-hardened and developed on otherwise smooth 

rock. 

clastic. Rock or sediment made of fragments of preexisting rocks. 

columnar joints. Planar or curvilinear fractures that 

bound polygonal columns of rock. Typically form due 

to contraction during cooling of volcanic rocks. 

conglomerate. A coarse-grained sedimentary rock with 

clasts >2 mm (0.08 in) in a fine-grained matrix. 

continental crust. The type of crustal rocks underlying 

the continents and continental shelves; having a 

thickness of 25–60 km (16–37 mi)and a density of 

approximately 2.7 grams per cubic centimeter. 

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. 

craton. The relatively old and geologically stable interior 

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

cross-bedding. Uniform to highly varied sets of inclined 

sedimentary beds deposited by wind or water. 

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

(6–25 mi) thick, consisting predominantly of relatively 

low-density silicate minerals (also see oceanic crust 

and continental crust). 

dacite. A volcanic rock with about 63–69% silica. 

debris flow. A moving mass of rock fragments, soil, and 

mud; more than half the particles being larger than 

sand size. 

deformation. A general term for the process of faulting, 

folding, shearing, extension, or compression of rocks 

as a result of various Earth forces. 

devitrification. Conversion of glass to crystalline 

material. 

dike. A tabular, discordant igneous intrusion. 

dip. The angle between a structural surface and a 

horizontal reference plane measured normal to their 

line of intersection. 

distal. A sedimentary deposit consisting of fine clastics 

that formed farthest from the source area. 

dolomite. A carbonate sedimentary rock consisting of 

>50% of the mineral dolomite (calcium-magnesium 

carbonate). 
32 NPS Geologic Resources Division 

epicontinental. Situated on the continental shelf or on 

the continental interior, as a epicontinental sea. 

euhedral. A grain bounded by perfect crystal faces. 

eutaxitic. Said of the banded structure in certain 

extrusive rocks, resulting from the parallel 

arrangement and alteration of layers of different 

textures, mineral composition, or color. 

extrusive. Of or pertaining to the eruption of igneous 

material onto Earth’s surface. 

facies (metamorphic). Rocks of any origin formed within 

certain pressure-temperature conditions. 

fault. A subplanar break in rock along which relative 

movement occurs between the two sides. 

feldspar. The most common mineral group in the 

shallow levels of Earth’s crust. Composed of 

combinations of potassium, sodium, and calcium 

combined with aluminum and silica. 

fiamme. Italian for “flame.” Refers to lens-shaped, 

flattened pumice fragments in a welded tuff. In crosssection such fragments commonly have jagged 

terminations, giving the appearance of flames. 

flow ramp. A sequence of layers in a lava flow that ramp 

abruptly upward. Most common in high-silica 

(rhyolite) lavas due to their high viscosity. 

footwall. The mass of rock beneath a fault, orebody, or 

mine working, especially the wall rock beneath an 

inclined vein or fault. 

formation. Fundamental rock-stratigraphic unit that is 

mappable and lithologically distinct from adjoining 

strata and has definable upper and lower contacts. 

fracture. Irregular breakage of a mineral; also any break 

in a rock (e.g., crack, joint, or fault). 

frost wedging. The breakup of rock due to the expansion 

of water freezing in fractures. 

fumarole pipes. Steam vents within volcanic rocks that 

result from degassing after deposition of ash-flow 

deposits, or from steam from underlying wet ground. 

graben. A down-dropped structural block bounded by 

steeply dipping, normal faults (also see horst). 

graded bedding. The result of gravitational settling of 

particles in a fluid which results in larger and heavier 

grains being concentrated at the base of a deposit.. 

granite. A high-silica rock (typically more than 70% 

silica) composed mainly of coarse-grained crystals of 

quartz and feldspar. 

granophyre. An irregular microscopic intergrowth of 

quartz and alkali feldspar. 

hanging wall. The overlying side of an orebody, fault, or 

mine working, especially the wall rock above an 

inclined vein or fault. 

hoodoo. A pillar of rock developed by erosion of 

horizontal strata of varying hardness. Typically found 

in climatic zones where most rainfall is concentrated 

during a short period of the year. 

horst. An uplifted structural block bounded by highangle normal faults (also see graben). 

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 older 

rock. The invading rock may be a plastic solid or 

magma that pushes its way into the older rock. 

inverse grading. Graded bedding in which larger grains 

settle above smaller ones. Indicates rapid lateral flow. 

A characteristic feature of surge beds. 

island arc. A line or arc of volcanic islands formed over 

and parallel to a subduction zone. 

joint. A semi-planar break in rock without relative 

movement on either side of the fracture surface. 

lahar. A mudflow composed chiefly of volcaniclastic 

materials on the flank of a volcano. 

landslide. Any process or landform resulting from rapid, 

gravity-driven mass movement. 

lava. Fluid rock that issues from a volcano or fissure; 

also, the same material solidified by cooling. 

Liesegang bands. Secondary, nested rings or bands 

caused by chemical deposition from a fluid that 

migrated through the pore space of the rock. 

limestone. A sedimentary rock consisting chiefly of 

calcium carbonate. 

lithology. The physical description of a rock, especially 

its color, mineralogic composition, and grain size. 

lithophysa. A hollow, bubble-like structure composed of 

concentric shells of finely crystalline alkali feldspar, 

quartz, and other minerals; found in volcanic rocks 

containing abundant silica. 

lithosphere. Earth’s relatively rigid outmost shell, 50–100 

km (30–60 mi) thick that encompasses the crust and 

uppermost mantle. 

magma. Molten rock capable of intrusion and extrusion. 

magma chamber. A reservoir of molten rock beneath 

Earth’s surface. 

mantle. The zone between Earth’s crust and core. 

matrix. The groundmass of an igneous rock or the finer 

grained material enclosing the larger grains in a 

sedimentary rock; also the rock or sediment in which a 

fossil is embedded. 

mechanical weathering. The physical breakup of rocks 

without change in composition. 

megashear. A strike-slip fault with a horizontal 

displacement measured in tens to hundreds of 

kilometers. 

member. A lithostratigraphic unit with definable 

contacts; a member subdivides a formation. 

metamorphic. Pertaining to the process of 

metamorphism or its results. 

metamorphism. Literally, “change in form.” 

Metamorphism occurs in rocks through mineral 

alteration, genesis, and/or recrystallization from 

increased heat and pressure. 

mineral. A naturally occurring, inorganic crystalline solid 

with a definite chemical composition. 

moat. An annular depression between the central 

resurgent dome and the edge of a caldera depression. 

neck (volcanic). An eroded, vertical, pipe-like intrusion 

that represents the vent of a volcano. 

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

moves down relative to the footwall. 

nuée ardente. A “glowing cloud” of hot ash that rises 

from an avalanche of volcanic ash and rock fragments. 

A type of pyroclastic flow. 

oceanic crust. Earth’s crust formed at spreading ridges 

that underlie the ocean basins. Oceanic crust is 6–7 km 

(3–4 mi) thick and generally of basaltic composition. 

orogeny. A mountain-building event. 
CHIR Geologic Resource Inventory Report 33 

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 geography from past 

geologic periods. 

parent (rock). The original rock from which sediments or 

other rocks are derived. 

perlitic. Said of the texture of glassy volcanic rocks 

characterized by numerous curving cracks roughly 

concentric around closely spaced centers. 

phenocryst. A coarse crystal in a porphyritic igneous 

rock. 

pillow lava. Lava that flowed under water and formed 

pillow-shaped masses as a consequence of chilling and 

solidification of the outer surface while the inner part 

of the lava flow was still flowing. 

plate tectonics. The theory that the lithosphere is broken 

up into a series of rigid plates that move over Earth’s 

surface above a more fluid aesthenosphere. 

pluton. A body of intrusive igneous rock. 

porphyry. An igneous rock with abundant coarse crystals 

in a fine-grained groundmass. 

proximal. A sedimentary deposit consisting of coarse 

clastics that formed nearest the source area. 

pumice. A gas-bubble-rich volcanic rock typically with 

enough bubbles to allow it to float in water. 

pyroclastic. Clastic rock material formed by volcanic 

explosion or aerial expulsion from a volcanic vent; also 

pertaining to rock texture of explosive origin. 

pyroclastic flow. A dense could of hot ash, rock debris, 

pumice, and gas that moves rapidly downslope from a 

volcano and leaves an ash-rich deposit. 

radioactivity. The spontaneous decay or breakdown of 

unstable atomic nuclei. 

radiometric age. An age in years determined from 

radioisotopes and their decay products. 

relative dating. Determining the ageof rocks, events, or 

fossils without reference to their absolute age. 

resurgent dome. A region of domal uplift within a 

caldera depression. 

reverse fault. A contractional, high-angle (>45°), dip-slip 

fault in which the hanging wall moves up relative to the 

footwall (also see “thrust fault”). 

reomorphic. Said of a rock whose form and internal 

structure indicate that it was subjected to ductile flow; 

also, the phenomena causing such a rock. 

rhyolite. A silica-rich volcanic rock or magma (>70% 

silica). 

sandstone. Clastic sedimentary rock of predominantly 

sand-sized grains. 

schist. A metamorphic rock that is rich in the platy 

mineral mica. 

sediment. An eroded and deposited, unconsolidated 

accumulation of lithic and mineral fragments. 

sedimentary rock. A consolidated and lithified rock 

consisting of detrital and/or chemical sediment(s). 

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. 

sill. A tabular, igneous intrusion that is concordant with 

the country rock. 

siltstone. A variably lithified sedimentary rock composed 

of silt-sized grains. 

slope. The inclined surface of any geomorphic feature or 

rational measurement thereof (syn: gradient). 

slump. A generally large, coherent mass movement with 

a concave-up failure surface and subsequent backward 

rotation relative to the slope. 

spherulites. A spherical mass produced by crystallization 

of volcanic glass at high temperature and typically 

composed of minute crystal fibers of feldspar that 

radiate from a common point. 

spreading ridges. The globe-encircling submarine 

mountain ranges where the oceanic sea floor and crust 

is created by upwelling and eruption of basalt magma.. 

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

rock. 

stratigraphy. The geologic study of the origin, 

occurrence, distribution, classification, correlation, 

and age of rock layers, especially sedimentary rocks. 

strike. The compass direction of the line of intersection 

that an inclined surface makes with a horizontal plane. 

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

relative movement is parallel to the strike of the fault. 

structure. The attitude and relative positions of the rock 

masses of an area resulting from such processes as 

faulting, folding, and igneous intrusions. 

subduction zone. A convergent plate boundary where 

oceanic lithosphere descends beneath a continental or 

oceanic plate and is carried down into the mantle. 

subhedral. A grain partly bounded by crystal faces; 

intermediate between euhedral and anhedral. 

surge beds. Ash-rich beds that result from laterallydirected volcanic blasts. Characterized by inverse 

grading and low-angle cross-bedding. 

tectonic. Relating to large-scale movement and 

deformation of Earth’s crust. 

thrust fault. A contractional fault with a shallowly 

dipping fault surface (<45°

) where the hanging wall 

moves up and over relative to the footwall. 

topography. The general morphology of Earth’s surface, 

including relief and location of natural and 

anthropogenic features. 

trace (fault). The exposed intersection of a fault with 

Earth’s surface. 

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). 

trend. The direction or azimuth of elongation of a linear 

geologic feature. 

tuff. Generally fine-grained, igneous rock formed of 

consolidated volcanic ash. 

unconformity. A surface within sedimentary strata that 

marks a prolonged period of nondeposition or 

erosion. 

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

movement that raises the rocks. 

vent. An opening at Earth’s surface through which 

volcanic materials are extruded. 

vitrophyre. Dense volcanic glass produced by extreme 

welding at the base of a welded tuff deposit. 

volcanic. Related to volcanoes; describes igneous rock 

crystallized at or near Earth’s surface (e.g., lava). 

volcaniclastic. All clastic volcanic materials formed by 

any process of fragmentation, dispersed by any kind of 

transporting agent, deposited in any environment, or 
34 NPS Geologic Resources Division 

mixed in any significant proportion with nonvolcanic 

fragments. 

weathering. The set of physical, chemical, and biological 

processes by which rock is broken down in place. 

welded tuff. A pyroclastic rock that has been hardened 

by the welding together of its glass shards under the 

combined action of heat, pressure, and hot gases. 

xenocryst. A crystal that resembles a phenocryst in 

igneous rock but is a secondary mineral, forming after 

solidification of the rock in which it occurs.
CHIR Geologic Resource Inventory Report 35 

References 

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

available from the National Park Service Geologic Resources Division. 

Anderson, J. L. 1988. Core complexes of the MojaveSonoran Desert: Conditions of plutonism, 

mylonitization, and decompression. In Metamorphism 

and crustal evolution of the western United States, ed. W. 

G. Ernst, 502-525. Englewood Cliffs, N.J.: Prentice 

Hall. 

Anderson, T. H., and J. A. Nourse. 2005. Pull-apart basins 

at releasing bends of the sinistral Late Jurassic MojaveSonora fault system. Special Paper 393. Boulder, CO: 

Geological Society of America. 

Becker, L., R. J. Poreda, A. G. Hunt, T. E. Bunch, and M. 

Rampino. 2001. Impact event at the Permian-Triassic 

boundary: Evidence from extraterrestrial noble gases 

in fullerenes. Science 291 (5508): 1530-1533. 

Bezy, J. V. 2001. Rocks in the Chiricahua National 

Monument and the Fort Bowie National Historic Site. 

Down-to-Earth 11. Tucson, AZ: Arizona Geological 

Survey. 

Biek, R. F., G. C. Willis, M. D. Hylland, and H. H. 

Doelling. 2000. Geology of Zion National Park, Utah. 

In Geology of Utah’s Parks and Monuments, ed. D. A. 

Sprinkel, T. C. Chidsey, Jr., and P. B. Anderson, 107-

138. Salt Lake City, UT: Utah Geological Association 

Publication 28. 

Bilodeau, W. L., and F. A. Lindberg. 1983. Early 

Cretaceous tectonics and sedimentation in southern 

Arizona, southwestern New Mexico, and northern 

Sonora, Mexico. In Mesozoic paleogeography of westcentral United States, ed. M. W. Reynolds and E. D. 

Dolly, 173-188. Denver: Rocky Mountain Section, 

Society of Economic Paleontologists and 

Mineralogists. 

Blakey, R. C. 1980. Pennsylvanian and Early Permian 

paleogeography, southern Colorado Plateau and 

vicinity. In Paleozoic paleogeography of west-central 

United States, ed. T. D. Fouch and E. R. Magathan, 

239-258. Denver, CO: Rocky Mountain Section, 

Society of Economic Paleontologists and 

Mineralogists. 

Chronic, H. 1983. Roadside geology of Arizona. 

Missoula: Mountain Press Publishing Company. 

Dickinson, W. R., and T. F. Lawton. 2001. Tectonic 

setting and sandstone petrofacies of the Bisbee Basin 

(USA-Mexico). Journal of South American Earth 

Sciences 14 (5): 474-504. 

Drewes, H. 1981. Geologic map and sections of the Bowie 

Mountain South quadrangle, Cochise County, Arizona. 

Scale 1:24,000. Miscellaneous Investigations Series 

Map I-1363. Reston, VA: U.S. Geological Survey. 

Elder, W. P., and J. I. Kirkland. 1994. Cretaceous 

paleogeography of the southern Western Interior 

Region. In Mesozoic systems of the Rocky Mountain 

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

Franczyk, 415-440. Denver, CO: Rocky Mountain 

Section, Society for Sedimentary Geology. 

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

Chihuahua Trough; a Jurassic pull-apart basin. Special 

Paper 393. Boulder, CO: Geological Society of 

America. 

Hall, D. B. 1996. Modelling failure of natural rock 

columns. Geomorphology 15: 123-134. 

Hoffman, P. F. 1989. Precambrian geology and tectonic 

history of North America. In The geology of North 

America: An overview, ed. A. W. Bally and A. R. 

Palmer, 447-512. Boulder, CO: Geological Society of 

America, The Geology of North America-A. 

Kauffman, E. G., 1977, Geological and biological 

overview: Western Interior Cretaceous basin. 

Mountain Geologist 14: 75-99. 

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

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

Morris, T. H., V. W. Manning, and S. M. Ritter. 2000. 

Geology of Capitol Reef National Park, Utah. In 

Geology of Utah’s Parks and Monuments, ed. D. A. 

Sprinkel, T. C. Chidsey, Jr., and P. B. Anderson, 85-

106. Salt Lake City, UT: Utah Geological Association 

Publication 28. 

National Park Service. 2001. Record of decision: Final 

Chiricahua general management plan and final 

environmental impact statement Chiricahua National 

Monument: Arizona. 

http://legalminds.lp.findlaw.com/list/epaimpact/msg06376.html. 

Pallister, J. S., and E. A. du Bray. 1997. Interpretive map 

and guide to the volcanic geology of Chiricahua National 

Monument and vicinity, Cochise County, Arizona. Scale 

1:24,000. Miscellaneous Investigations Series Map I2541. Reston, VA: U.S. Geological Survey. 
36 NPS Geologic Resources Division 

Pallister, J. S., E. A. du Bray, and D. B. Hall. 1997. Guide 

to the volcanic geology of Chiricahua National 

Monument and vicinity, Cochise County, Arizona. 

Pamphlet to accompany the Miscellaneous 

Investigations Series Map I-2541. Reston, VA: U.S. 

Geological Survey. 

Peterson, J. A. 1980. Permian paleogeography and 

sedimentary provinces, west central United States. In 

Paleozoic paleogeography of west-central United States, 

ed. T. D. Fouch and E. R. Magathan, 271-292. Denver, 

CO: Rocky Mountain Section, Society of Economic 

Paleontologists and Mineralogists.

Raup, D. M. 1991. Extinction: Bad genes or bad luck? 

New York: W.W. Norton and Company. 

Tweet, J. S., V. L. Santucci, and J. P. Kenworthy. 2008. 

Paleontological resource inventory and monitoring—

Sonoran Desert Network. Natural Resource Technical 

Report NPS/NRPC/NRTR—2008/130. Fort Collins, 

CO: National Park Service. 
CHIR Geologic Resource Inventory Report 37 

Appendix A: Geologic Map Graphic 

The following page is a snapshot of the geologic map for Chiricahua National 

Monument. For a poster-size PDF of this map or for digital geologic map data, please see 

the included CD or visit the Geologic Resources Inventory publications Web page 

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

CHIR Geologic Resource Inventory Report 39 

Appendix B: Scoping Summary 

The following excerpts are from the GRI scoping summary for Chiricahua National 

Monument. The contact information and Web addresses in this appendix may be 

outdated. Please contact the Geologic Resources Division for current information. 

The National Park Service held a GRI scoping meeting 

for Chiricahua National Monument (CHIR) on April 5, 

2006, at park headquarters. Participants at the meeting 

included NPS staff from the park, Geologic Resources 

Division, and the Intermountain Region and cooperators 

from the United States Geological Survey (USGS), 

Arizona Geological Survey (AZGS), and Colorado State 

University (CSU) (see scoping table 3). 

Park and Geologic Setting 

Chiricahua National Monument was proclaimed a 

national monument on April 18, 1924, and transferred 

from the U.S. Department of Agriculture, Forest Service 

to the National Park Service on August 10, 1933. It 

presently encompasses 11,984.73 acres in extreme 

southeastern Arizona. In 1976, Congress designated 

10,290 acres as Wilderness (86% of the Monument). 

Chiricahua NM was established to protect and preserve 

the exceptional geologic features in the Monument 

including pinnacles, columns, spires and balanced rocks. 

Geologic Mapping for Chiricahua National Monument 

The NPS GRI Geology-GIS Geodatabase Data Model 

incorporates the standards of digital map creation set for 

the GRI Program. Staff members digitize maps or 

convert digital data to the GRI digital geologic map 

model using ESRI ArcMap software. Final digital 

geologic map products include data in geodatabase, 

shapefile, and coverage format, layer files, FGDCcompliant metadata, and a Windows HelpFile that 

captures ancillary map data. 

When possible, the GRI program provides large scale 

(1:24,000) digital geologic map coverage for each park’s 

area of interest, which is often composed of the 7.5-

minute quadrangles that contain park lands (fig. 1). Maps 

of this scale (and larger) are useful to resource 

management because they capture most geologic features 

of interest and are positionally accurate within 12 m (40 

ft). The process of selecting maps for management use 

begins with the identification of existing geologic maps 

and mapping needs in the vicinity of the park. Scoping 

session participants then select appropriate source maps 

for the digital geologic data to be derived by GRI staff. 

Map coverage for Chiricahua NM consists of 4 

quadrangles of interest mapped at a 1:24,000 scale 

(scoping fig. 1): Cochise Head, Bowie Mountain South, 

Rustler Peak, and Fife Peak. These quadrangles are 

located on the Wilcox and Chiricahua Peak 30’ x 60’ 

sheets. Table 1 lists the source maps chosen for 

Chiricahua National Monument. 

GRI staff have digitized GMAP 1120: 

Pallister, J. S., and E. A. du Bray. 1997. Interpretive map 

and guide to the volcanic geology of Chiricahua National 

Monument and vicinity, Cochise County, Arizona. Scale 

1:24,000. Miscellaneous Investigations Series Map I2541. U.S. Geological Survey. 

GMAP 1120 covers to the park boundary. The four 

intersecting 7.5’ quadrangles do have complete geologic 

map coverage, and if it is desired to have more of a buffer 

around the park, they could be digitized to enhance the 

existing digital geologic map. 

GMAP 1120 is probably the best map available (Ed du 

Bray). The map focuses on the Turkey Creek caldera and 

surrounding area and contains an interpretive pamphlet 

suitable for the non-geologist. Ed du Bray considers 

GMAP 1120, however, to be a map that simply lays out 

the geologic framework of the park. More detailed 

mapping and subsequent research could be done, for 

example, on the world-class tuff deposits in Chiricahua. 

GMAP 1120 is sold at the Visitor Center. 

Both the Paleozoic rocks in the northeastern part of 

Chiricahua NM and the Mesozoic rocks were difficult to 

map (Ed du Bray). Harald Drewes mapped the Paleozoic 

rocks in detail, but structural relations among these strata 

could probably be refined. 
40 NPS Geologic Resources Division 

Scoping table 1. GRI Mapping Plan for Chiricahua National Monument. 

Covered 

Quadrangle

s 

GMAP* Citation Scale Format Assessment GRI Action 

Parts of 

Bowie 

Mountain 

South, 

Cochise 

Head, 

Rustler Park, 

Fife Peak 

1120 Pallister, J. S., and E. A. duBray. 

1997. Interpretive map and guide 

to the volcanic geology of 

Chiricahua National Monument 

and vicinity, Cochise County, 

Arizona. Scale 1:24,000. Map I2541. Reston, VA: US Geological 

Survey. 

1: 24,000 paper GMAP 1120 

covers the park 

boundary 

Conversion of 

digital data to 

geodatabase 

data model will 

integrate into 

either FY06 or 

FY07 projects. 

Rustler Park 8436 Pallister, J. S., E. A. duBray, and J. 

S. Latta. 1994. Geologic map of the 

Rustler Park quadrangle, Cochise 

County, Arizona. Scale 1:24,000. 

Geologic Quadrangle Map GQ1696. Reston, VA: US Geological 

Survey. 

1: 24,000 paper 

and 

digital 

Maps Rustler Peak 

quadrangle and 

includes 

southeastern part 

of Monument 

Conversion of 

digital data to 

geodatabase 

data model/ will 

integrate into 

either FY06 or 

FY07 projects. 

Fife Peak 8439 Pallister, J. S., and E. A. duBray. 

1994. Geologic map of the Fife 

Peak quadrangle, Cochise County, 

Arizona. Scale 1;24,000. Geologic 

Quadrangle Map GQ-1708. 

Reston, VA: US Geological 

Survey. 

1: 24,000 digital Maps Fife Peak 

quadrangle, the 

quadrangle 

bordering the 

monument to the 

southwest 

Conversion of 

digital data to 

geodatabase 

data model/ will 

integrate into 

either FY06 or 

FY07 projects. 

* GMAP numbers are unique identification codes used in the GRI database 

Scoping figure 1. Quadrangles of Interest for Chiricahua National Monument, Arizona. The 7.5-minute quadrangles 

(scale 1:24,000) are labeled in black; names in yellow indicate 30-minute by 60-minute quadrangles (scale 1:100,000). 

Green outline indicates the boundary of the Monument. 
CHIR Geologic Resource Inventory Report 41 

Quaternary, surficial deposits at Chiricahua NM have 

not been mapped in detail although most every structure 

in the Monument is built on Quaternary deposits (Todd 

Shipman, AZGS; Ed du Bray). The Monument has a soils 

map, but the map has not been digitized (Carrie Dennett, 

NPS CHIR). Rhyolitic volcanic ash deposited in water 

alters to bentonite, a clay that has shrink and swell 

properties. Soils with shrink and swell characteristics and 

thin soils both could impact septic systems and the 

structural integrity of facilities so a soils map is important 

to the park. Pete Biggam (NPS GRD) should be 

consulted for questions regarding soils. 

Because of the flooding potential at the Visitor Center 

expansion and campgrounds, a map of the Quaternary 

showing potential flood areas would be beneficial. Mike 

Martin (NPS WRD) visited Chiricahua NM and 

generated a 100-year flood map. Stephanie will contact 

Mike to see about digitizing his map for Chiricahua. 

Colleen Filippone (NPS Intermountain Region) also 

would like a copy of the map for the Chiricahua NM 

library. 

Increased runoff and flooding associated with recent 

fires is an issue at the Monument (Carrie Dennett). Fire 

increases the potential for slope erosion, and hazard 

maps showing areas prone to mass slippage would be 

useful for management. Hazard maps showing rock 

outcrops as natural fire barriers and areas of recent burns 

could also be helpful to park staff. Ed du Bray suggested 

that remote sensing could be used for this. 

Colleen Filippone expressed an interest in more map 

coverage in Pine Canyon because of high visitation. Pine 

Canyon is located along the southern edge of GMAP 

1120. 

GRI mapping action planned for FY 2006 or FY 2007 

includes: 

• The GRI will convert existing digital data for GMAP 

1120 from the GRI coverage and shapefile data model 

to the GRI geodatabase data model. This is required, 

as integration of newly acquired digital data will need 

to be in the same GIS format for edge-matching and 

compilation, and because the geodatabase format is 

now the standard GRI supported deliverable format. 

• Ed du Bray of the USGS has recently supplied the GRI 

(acquisition date of April 17, 2006) with digital data in 

Shapefile (.shp) format, as well as digital text of 

ancillary text including map unit descriptions and 

references pertaining to GMAP 8436 (Rustler Park) 

and 8439 (Fife Peak quadrangle). The GRI will 

evaluate and convert the digital data to the GRI 

geodatabase data model format. The digital data will 

then be edge-matched and appended to existing GRI 

digital data GMAP 1120 to produce one compiled park 

map for Chiricahua NM. Ancillary text and figures 

associated with the two quadrangle maps will be 

formatted and incorporated with existing GRI CHIR 

project text and figures. 

• The GRI will contact Mike Martin (NPS Water 

Resources Division) in Fort Collins concerning a 

floodplain map he recently produced for Chiricahua 

NM. The GRI will then determine if the map can be 

georeferenced for GIS digitization (this requires 

coordinate tics and/or features present that can be 

used to assist georeferencing). If georeferencing is 

possible then the GRI will digitize the map to the GRI 

geodatabase data model format. 

• The GRI will evaluate a scoping proposal to map 

Quaternary surficial deposits within the Monument, 

primarily deposited within drainages. This should 

prove helpful for debris flow and post-fire 

management. 

• The GRI will evaluate a scoping proposal to re-map 

the area around the King of Lead Mine in and near the 

northeast area of the park. Ed du Bray stated that 

geology of the area was structurally complex and could 

be re-mapped by a geologist with more structural 

mapping experience. 

Geologic Resource Management Issues 

The scoping session for Chiricahua National Monument 

provided the opportunity to develop a list of geologic 

issues, features and processes, which will be further 

explained in the final GRI report. Scoping table 2 

presents a summary of potential hazards or features 

discussed during the scoping meeting and the issues 

these hazards may present to management. 

During the meeting, Alan Whalon (NPS CHIR-FOBO) 

prioritized the most significant issues as follows: 

(1) Flooding 

(2) Sewer and septic problems, and 

(3) Information for interpretation 

Other geologic resource management issues discussed 

included: mining issues, landslides, mineral specimen 

collecting, subsurface contamination from a leaking 

underground storage tank, and rock stability associated 

with fractures and faults in the rocks. 
42 NPS Geologic Resources Division 

Scoping table 2: Hazards associated with issues, features, and processes at Chiricahua National Monument. 

Hazard Issues, Feature and Processes 

Flooding Large watershed catchment area; affects Visitor Center & campgrounds 

Septic Thin soils; bentonite; flooding 

Shrink and swell soils Expansive clays; shrink and swell properties 

Interpretive needs Displays are not geologically correct 

Landslides Potential for large landslides in southeast Chiricahua NM & along Sugarloaf Trail 

Old mines Safety issues; acid mine drainage? 

Mineral and/or rock collecting Spherulites – collected by visitors; mineral (Pb/Zn) specimens 

Post-fire erosion Steep slopes denuded by fire tend to erode 

Rock climbing Not allowed in park 

Seismicity Not a significant issue for the pinnacle features and columns 

Caves/karst Not an issue 

Geothermal Not an issue 

Active faults Not an issue 

Flooding 

Mike Martin advised the Monument that slopes were so 

steep, flooding would occur too quickly for evacuation 

(Carrie Dennett). Todd Shipman (AZGS) suggested that 

rather than developing a warning system, which would 

not be adequate, the Monument could identify areas 

prone to flooding and avoid locating facilities in those 

areas. Carrie Dennett pointed out that, unfortunately, the 

Visitor Center and campgrounds are located in the 

floodplain, and the Monument has no plans to relocate 

those facilities. Campgrounds have been closed in the 

past due to 100-year floods. Monument management is 

concerned that visitors new to the area won’t recognize 

the potential for flooding in the campgrounds because 

they see the area as a “desert” (Alan Whalon). 

Sewer and Septic Problems 

Issues associated with the sewer and septic system at 

Chiricahua National Monument may be more related to 

money than to geology (Alan Whalon). The septic system 

is old and deteriorating. A good location for a septic 

system is difficult to find. 

Information for Interpretation 

The interpretive displays at Sugarloaf Mountain need to 

be redone (Ed du Bray). These displays show a 

stratovolcano with steep slopes, but the Turkey Creek 

caldera was a gently sloping volcano that erupted 

through ring fractures, not a central vent. Alan Whalon 

commented that the Monument focused on the pinnacle 

features, but the whole geologic story is much more 

interesting. However, a geologist has not been employed 

by Chiricahua National Monument for some time. 

Suzanne Moody (NPS CHIR) suggested a need to 

emphasize the caldera study in their interpretive 

material. The geology of Chiricahua NM might be used 

to tie in other themes such as natural history, culture, 

vegetation, and biology. 

Other Issues 

The King of Lead Mine, adjacent to the northeast 

boundary of Chiricahua NM, consists of four patented 

mining claims. The mine was active up to about 1984 

when access to the mine through the Monument became 

an issue. The lead-zinc deposits of the mine formed as a 

result of magma interacting with Paleozoic rocks and 

may be related to an unknown caldera around Cochise 

Head. Several other small, lead-zinc deposits are 

associated with Turkey Creek caldera magmatism. These 

mines, including the King of Lead Mine, are presently 

not economically exploitable. 

Acid mine drainage from mines adjacent to Chiricahua 

National Monument may be an issue. The King of Lead 

mine drains to Bonita Creek. There is no surface flow for 

Most of the year, however. Mike Martin performed 

some water quality tests and was skeptical of the results, 

which showed no impacts (Colleen Filippone). If funds 

for sampling could be found, groundwater sampling 

might prove beneficial. The mine owner would sell the 

mine to the Monument for several million dollars. Alan 

Whalon explained that old mines were an issue about ten 

years ago, but today there are no safety or bat habitat 

issues. 

Vast landslide deposits of an unknown age are located in 

the southeastern area of Chiricahua NM (Ed du Bray), 

creating the potential for large landslides. A slump 

recently occurred along the Sugarloaf trail closing it for 

1.5 years. The slump is associated with a distinctive white 

volcanic ash zone that is easily eroded, undercuts the 

overlying cliff, and results in collapse. Washouts along a 

Civilian Conservation Corps (CCC) trail during trail 

rehabilitation closed the trail for six months. 

Collecting mineral specimens probably is more of a 

Monument management issue than is hardrock mining 

for economic mineral deposits. In addition to lead-zinc 

mineral specimens (galena, sphalerite), spherulite 

collecting is an issue for management. The marble-like 

spherulites (nicknamed “hailstones”) weather out of 

volcanic tuff along the Hailstone Trail. 

Regarding subsurface contamination (soil and 

groundwater), an underground storage tank was pulled 

out in 1994 and found to be leaking. Decontamination 

continues because the geometry of the contaminant 

plume is difficult to define and mitigate (Alan Whalon). 

Although horizontal and vertical fractures cut the rocks, 

a study of some of these structures showed that they are 
CHIR Geologic Resource Inventory Report 43 

stable (Ed du Bray). In 1887, a 7.2 M earthquake (the 

Pitaycachi earthquake) did not destabilize the columns. 

During a road project, a large rock fell on the road 

following a rainfall (Alan Whalon). Seismometers were 

placed in the area to detect vibrations from heavy 

equipment and from small dynamite charges. This small 

but “interesting” study suggested that one of the biggest 

issues regarding rockfall was climbing on the rocks (Alan 

Whalon). Chiricahua NM does not allow climbing and 

the study is additional evidence for not allowing this 

recreational activity in the Monument. 

Features and Processes 

Ed du Bray led a field trip to the top of Sugarloaf 

Mountain to observe features related to the Turkey 

Creek caldera. Features observed along the Sugarloaf 

Trail included: 

• Pinnacles, columns, spires, and balanced rocks, 

• Erosional remnants of igneous dikes exposed near the 

King of Lead Mine, 

• Middle and Upper Members of the Rhyolite Canyon 

Tuff and associated features, 

• Remnants of the slump resulting from erosion of the 

conspicuous white ash unit and undercutting of the 

Upper Member, 

• Structures that suggest the white ash unit is a surge 

deposit at the base of the Upper Member rather the an 

ash cloud deposit at the top of the Middle Member, 

• Fumarole pipes, 

• The “boiling pot” of a fumaroles, 

• Liesegang bands where small amounts of chemical 

impurities from hot water were precipitated, 

• The only place in the Chiricahua Mountains where the 

dynamic contact between the Middle and Upper 

Members is exposed, 

• An overall panoramic display of the caldera remnants 

from the top of the mountain. 

Other geologic features in Chiricahua National 

Monument include: 

• Columnar joints in the rhyolite, 

• Spherulites (marble-like rocks found along Hailstone 

Trail), 

• Vertical volcanic flow structures, 

• Landslides and mass wasting features (erosional 

processes), 

• Vertical and horizontal fractures (tectonic and cooling 

processes), 

• Inverted topography. 

Recommendations 

Recommendations from the scoping meeting include: 

• More detailed mapping and research on the tuff 

deposits, 

• Maps showing the relationship between geology and 

vegetation, 

• A map identifying flood prone areas, 

• A hazard map showing rock outcrops and potential 

post-fire slope failure. 

Scoping table 3. Scoping Meeting Participants. 

Name Affiliation Position Phone E-Mail 

Covington, Sid Geologist NPS GRD 303-969-2154 sid_covington@nps.gov 

Dennett, Carrie Ecologist NPS CHIR-FOBO 520-824-3560 

ext. 601 carrie_Dennett@nps.gov 

du Bray, Ed Geologist USGS 303-236-5591 edubray@usgs.gov 

Filippone, Colleen Hydrologist NPS, Intermountain Region 520-546-1607 colleen_filippone@nps.gov 

Graham, John Geologist Colorado State University 970-581-4203 rockdoc250@comcast.net 

Kerbo, Ron Cave specialist NPS GRD 303-969-2097 Ron_Kerbo@nps.gov 

Moody, Suzanne Park Ranger, 

Interpretation NPS CHIR 520-824-3560 

ext. 305 suzanne_moody@nps.gov 

Olsen, Ruth Biological 

Science Tech NPS CHIR-FOBO 520-824-3560 

ext. 602 ruth_olsen@nps.gov 

O’Meara, 

Stephanie Geologist Colorado State University 970-225-3584 Stephanie_O’Meara@partner.nps.gov 

Shipman, Todd Geologist Arizona Geol. Survey 520-770-3500 todd.shipman@azgs.az.gov 

Whalon, Alan Superintendent NPS CHIR-FOBO 520-824-3560 

ext. 202 alan_whalon@nps.gov 

Chiricahua National Monument 

Geologic Resources Inventory Report 

Natural Resource Report NPS/NRPC/GRD/NRR—2009/081 

National Park Service 

Acting Director • Dan Wenk 

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 the 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 

Geosciences and Restoration Branch Chief • Hal Pranger 

Credits 

Author • John Graham

Review • Ed du Bray and Pat O’Dell 

Editing • Diane Lane 

Digital Map Production • Anne Poole 

Map Layout Design • Josh Heise

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 D-94, June 2009 
EXPERIENCE YOUR AMERICATM 

National Park Service 

U.S. Department of the Interior 

Geologic Resources Division 

Natural Resource Program Center 

P.O. Box 25287 

Denver, CO 80225 

www.nature.nps.gov