Petrified Forest National Park 

Geologic Resources Inventory Report 

Natural Resource Report NPS/NRPC/GRD/NRR—2010/218 

National Park Service 

U.S. Department of the Interior 

Natural Resource Program Center 
THIS PAGE:

Much of the petrified wood in the 

park is Araucarioxylon arizonicum—

the state fossil of Arizona. These logs

are in the Rainbow Forest area of the 

park.

ON THE COVER:

Petrified Forest National Park was

established to preserve spectacular 

accumulations of Triassic-aged

petrified wood, between about 200 

and 220 million years old. The park

also preserves an excellent fossil 

vertebrate and plant record from the

“dawn of the Dinosaurs.”

National Park Service photographs by

T. Scott Williams. 
Petrified Forest National Park 

Geologic Resources Inventory Report 

Natural Resource Report NPS/NRPC/GRD/NRR—2010/218 

Geologic Resources Division 

Natural Resource Program Center 

P.O. Box 25287 

Denver, Colorado 80225 

June 2010 

U.S. Department of the Interior 

National Park Service 

Natural Resource Program Center 

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

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

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

environmental constituencies, and the public. 

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

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

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

management applicability. 

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

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

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

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

collection, analysis, or reporting of the data. 

Views, statements, findings, conclusions, recommendations, and data in this report do not 

necessarily reflect views and policies of the National Park Service, U.S. Department of the 

Interior. Mention of trade names or commercial products does not constitute endorsement or 

recommendation for use by the U. S. Government. 

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

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

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

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

NRPM). 

Please cite this publication as: 

KellerLynn, K. 2010. Petrified Forest National Park: geologic resources inventory report. 

Natural Resource Report NPS/NRPC/GRD/NRR—2010/218. National Park Service, Fort 

Collins, Colorado. 

NPS 110/104279, June 2010 

ii NPS Geologic Resources Division 
PEFO Geologic Resources Inventory Report iii

Contents

Lists of Figures and Tables ........................................................................................... iv

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

Acknowledgements..................................................................................................... vii

Credits....................................................................................................................................................................... vii

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

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

Park Setting .................................................................................................................................................................1

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

Petrified Wood.............................................................................................................................................................5

Paleontological Resource Damage................................................................................................................................6

Paleontological Resource Inventory...............................................................................................................................7

Paleontological Research..............................................................................................................................................8

Revisions to Stratigraphy ..............................................................................................................................................8

Bentonite.....................................................................................................................................................................9

Mass Wasting ............................................................................................................................................................10

Subsidence ................................................................................................................................................................10

Potash .......................................................................................................................................................................10

Liquefied Petroleum Gas Storage................................................................................................................................11

Uranium ....................................................................................................................................................................12

Adjacent Development...............................................................................................................................................12

Geologic Features and Processes................................................................................ 17

Paleontological Resources ..........................................................................................................................................17

Chinle Formation and Badlands Topography...............................................................................................................17

Unconformities..........................................................................................................................................................18

Structural Geology and Features.................................................................................................................................19

Sedimentary Structures ..............................................................................................................................................19

Eolian Features and Processes.....................................................................................................................................19

Volcanic Features.......................................................................................................................................................20

Stream Terraces.........................................................................................................................................................21

Tinajas.......................................................................................................................................................................21

Desert Varnish ...........................................................................................................................................................21

Caliche ......................................................................................................................................................................22

Map Unit Properties .................................................................................................... 28

Geologic History .......................................................................................................... 31

Mesa Redondo Member.............................................................................................................................................31

Blue Mesa Member....................................................................................................................................................31

Sonsela Member........................................................................................................................................................31

Petrified Forest Member.............................................................................................................................................32

Owl Rock Member.....................................................................................................................................................32

Jurassic and Cretaceous Rocks....................................................................................................................................32

Miocene-Pliocene and Quaternary Units.....................................................................................................................32

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

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

Additional References ................................................................................................. 45

Appendix A: Overview of Digital Geologic Data....................................................... 46

Appendix B: Scoping Session Participants ................................................................. 49

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

List of Figures

Figure 1. Map of Petrified Forest National Park...............................................................................................................viii

Figure 2. Agate House Pueblo..........................................................................................................................................3

Figure 3. Petrified wood projectile points.........................................................................................................................3

Figure 4. Colorado Plateau...............................................................................................................................................4

Figure 5. Petrified wood ................................................................................................................................................13

Figure 6. Bentonite........................................................................................................................................................14

Figure 7. Slump terraces................................................................................................................................................15

Figure 8. Cliff retreat .....................................................................................................................................................15

Figure 9. Holbrook Basin potash deposit ........................................................................................................................16

Figure 10. Fern fossil......................................................................................................................................................22

Figure 11. Placerias skeleton ..........................................................................................................................................23

Figure 12. Phytosaur skull..............................................................................................................................................23

Figure 13. Rainbow-colored petrified wood ...................................................................................................................24

Figure 14. Badlands topography ....................................................................................................................................24

Figure 15. Painted Desert...............................................................................................................................................25

Figure 16. Erosion..........................................................................................................................................................25

Figure 17. Unconformity................................................................................................................................................26

Figure 18. Hopi Buttes volcanic field ..............................................................................................................................26

Figure 19. Petroglyphs...................................................................................................................................................27

Figure 20. Geologic timescale.. ......................................................................................................................................33

Figure 21. Pangaea........................................................................................................................................................34

List of Tables

Table 1. Discoveries of significant vertebrate fossils at Petrified Forest National Park. ........................................................7

Table 2. Revised stratigraphy of the Chinle Formation. .....................................................................................................9

Table 3. Types of fossils in the Chinle Formation at Petrified Forest National Park............................................................22
PEFO Geologic Resources Inventory Report v

Executive Summary

This report accompanies the digital geologic map data for Petrified Forest National Park in 

Arizona, produced by the Geologic Resources Division 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 excellent exposures and accessibility of the Upper 

Triassic Chinle Formation make Petrified Forest 

National Park a world-renowned natural laboratory for 

paleontology and other geologic disciplines such as 

sedimentology, stratigraphy, geomorphology, and

structural geology. Petrified Forest National Park 

contains one of the largest and most colorful deposits of 

mineralized wood in the world. The park’s forests of 

petrified wood and other Upper Triassic fossil flora and 

fauna are globally significant because they provide a 

distinct record of diverse terrestrial ecosystems during 

“the dawn of dinosaurs” about 220 million years ago.

This period tracks the evolutionary transition of 

nonmarine animals, especially tetrapods. Scientists now 

recognize Petrified Forest National Park as one of the 

best places in the world to study these changes in the 

geologic record.

In addition to scientific study, the following issues could 

require attention from resource managers at Petrified 

Forest National Park:

• Petrified Wood. Congress set aside Petrified Forest 

National Park in order to preserve an incredible 

concentration of petrified wood. Over the years, 

attitudes about protection have ranged from 

permissible collection to today’s “zero tolerance” 

policy. The findings from social science studies about 

wood theft vary widely, making any estimates or 

analysis of the problem uncertain and questionable. 

However, the loss of the resource from within the 

expanded boundary and the invasive techniques used 

to unearth the buried remains highlight the need for 

continued protection. Furthermore, many visitors 

seem unable to resist the lure of taking a souvenir of 

petrified wood. 

• Paleontological Resource Damage. The ongoing 

paleontological inventory at Petrified Forest National 

Park has revealed that erosion and “poor science” are 

the primary causes of damage to vertebrate fossil 

resources. The National Park Service (NPS) has 

compiled various guidance documents, primarily the 

Natural Resource Management Reference Manual 77, 

to help managers avoid damage to paleontological 

resources. In addition, the Geological Society of 

America published a resource monitoring manual that 

suggests vital signs for paleontological resources. 

Active management remains the key to fossil 

preservation.

• Paleontological Resource Inventory. In 2001, resource 

managers at Petrified Forest National Park began to 

relocate and document all known paleontological 

sites, beginning with those containing vertebrate 

fossils. Although the scientific community and the 

public have recognized the fossil resources of the area 

for more than 150 years, the inventory has revealed 

anew the incredible wealth of fossil resources at the 

park. Petrified Forest National Park hosts a total of 

555 documented sites; the inventory has relocated 

more than 200 of these. However, the more than 

20,200 ha (50,000 ac) of very fossiliferous deposits puts 

a strain on the park’s small resource staff. Additional 

staff and trained volunteers would facilitate 

paleontological resource inventory and monitoring.

• Paleontological Research. Since 2000, park and 

cooperating paleontologists have published more than 

40 papers about the park’s paleontological resources, 

particularly fossil vertebrates but also fossil plants and 

microinvertebrates. Scientists from outside institutions 

who request and receive research permits have 

accomplished much of the paleontological research. 

The permitting system includes provisions to ensure 

that research activities comply with both Servicewide 

and park-specific requirements. Researchers provide 

copies of field data and submit an investigator’s annual 

report. Analysis identified the need for suitable space 

to conduct laboratory, office, and collection activities 

for on-site research. The lack of space for researchers 

could inhibit continued research.

• Revisions to Stratigraphy. The stratigraphic 

nomenclature at Petrified Forest National Park has 

been undergoing revisions since the early 1990s. Over 

the years, correlation of strata at the park has been 

contentious, and investigators have separated, 

combined, translated, and renamed various portions 

of the Chinle Formation. The exact age of the Chinle 

Formation is uncertain, but detailed geologic mapping 

and ongoing investigations will help define and clarify 

the formation’s age and significance.

• Bentonite. The picturesque mudstone beds of the 

Chinle Formation shape the beautiful badlands within 

the park. These beds contain bentonite—clay that has 

the ability to absorb large quantities of water 

accompanied by a large increase in volume. Rocks with 

bentonite swell when wet and shrink when dry, 

causing the ground surface to heave and buckle. The 

presence of bentonite, which contributes to the bare 

slopes and rapid erosion of badlands development, 

also creates sinkholes and pipes and affects the 

integrity of roads and buildings. 

• Mass Wasting. Features of mass wasting such as the 

downslope movement of bentonitic mudstone in the 

Chinle Formation, slump blocks along the cliffs of 
vi NPS Geologic Resources Division

Pintado Point, and cliff retreat near Newspaper Rock 

and along Blue Mesa could be of interpretive interest 

to park visitors. Such features could require attention 

and mitigation by resource managers. The severity of 

such problems is directly related to the extent of 

infrastructure in the affected areas. Early recognition, 

avoidance, or corrective engineering can mitigate the 

effects of mass wasting.

• Subsidence. The downward displacement of surface 

material affects the resources at Petrified Forest 

National Park on both small and large scales. For 

example, in 2005, a subsidence crack on the Blue Mesa 

Loop Road and the mesa edge required the technical 

assistance of the NPS Geologic Resources Division. 

On a larger scale, subsidence creates topographic 

features on the park’s landscape such as the Blue Mesa 

sink—a solution-collapse depression covering 1 km 

(0.6 mi) in diameter with surface relief of about 30 m 

(100 ft). 

• Potash. The dramatic increase in the price of potash, 

driven by the demand for fertilizer, has renewed 

interest in Arizona deposits, namely within the 

Holbrook Basin, which underlies a significant portion 

of Petrified Forest National Park. The stratigraphic 

location of the deposit would allow for underground 

mining techniques to exploit the potash, meaning that 

surface mining within the expanded boundaries of the 

park could be avoided. A single surface location could 

access the deposit, centralizing impacts; however, 

because of the deposit’s size, the surface footprint 

could cover hundreds of acres and require multiple 

work areas. 

• Liquefied Petroleum Gas Storage. Eleven storage 

caverns, part of Ferrell Liquefied Petroleum Gas 

Storage Facility, are located immediately west of the 

park boundary along the Burlington Northern Santa 

Fe Railway. These caverns do not present any 

immediate hazard to park resources, personnel, or 

visitors. However, because evacuation and closure of 

the park road east of the facility could be necessary in 

the event of a large spill or fire, the park 

superintendent should verify that they are on the 

storage facility’s emergency notification list. Park staff 

should maintain a good working relationship with 

state regulators and Ferrell Gas management.

• Uranium. The sandstone beds of the Chinle Formation 

are known to contain uranium. However, the potential 

for uranium mining on lands in or near the park is very 

low. Uranium exploration did occur in the Twin 

Buttes area of the park, but the nearest uranium mines 

are outside the park, north of Holbrook. The main 

resource management concern regarding uranium is 

protection of groundwater quality. Most of the 

observed radioactivity in the alluvial aquifer in the 

vicinity of the park is from natural sources rather than 

from effluent from mining and milling operations. 

Nevertheless, the U.S. Geological Survey and NPS 

Water Resources Division recommend that park 

managers continue annual sampling of the alluvial 

groundwater to determine whether significant water

quality changes have taken place. 

• Adjacent Development. The primary purpose of the 

2004 boundary expansion was to protect natural 

resources; however, it could have unforeseen 

consequences, namely population growth in the 

immediate vicinity of the park. At present, lands 

surrounding the park remain remote, with no access to 

water and no easy access to transportation routes. 

However, studies have shown that more and more 

people are choosing to move to “wilderness areas” 

based on quality of life choices. Adjacent development 

to the park and wilderness area could result in an 

increase in infrastructure, loss of important wildlife 

habitat, and threats to biodiversity. It could also drive 

up housing prices, resulting in a shortage of affordable 

rental units. Adjacent development could provide 

greater access to paleontological resources, and 

associated construction could increase erosion and 

reactivate eolian processes (e.g., dust storms).

The glossary contains definitions for many geologic 

terms used throughout this report and on the Map Unit 

Properties Table. For a geologic time scale, refer to

figure 20.
PEFO Geologic Resources Inventory Report vii

Acknowledgements

The Geologic Resources Inventory (GRI) is one of 12 inventories funded by the National 

Park Service Inventory and Monitoring Program. The GRI is administered by the 

Geologic Resources Division of the Natural Resource Program Center.

The Geologic Resources Division relies heavily on 

partnerships with institutions such as the U.S. 

Geological Survey, Colorado State University, state 

geologic surveys, local museums, and universities in 

developing GRI products.

Special thanks to: T. Scott Williams (Kalaupapa 

National Historical Park) who provided many NPS 

photographs for the report. Pat O’Dell (NPS Geologic 

Resources Division) provided information regarding 

potash mining and mineral rights in the Petrified 

Forest National Park area.

Credits

Author

Katie KellerLynn (NPS-Colorado State University)

Review

Bill Parker (Petrified Forest National Park)

Jeff Martz (Petrified Forest National Park)

Jason Kenworthy (NPS Geologic Resources Division)

Editing

Bonnie Dash (Envirocal)

Digital Geologic Data Production

James Chappell (NPS-Colorado State University)

Digital Geologic Data Overview Layout Design

Phil Reiker (NPS Geologic Resources Division)
viii NPS Geologic Resources Division

Figure 1. Map of Petrified Forest National Park. National Park Service graphic.
PEFO Geologic Resources Inventory Report 1

Introduction

The following section briefly describes the National Park Service Geologic Resources 

Inventory and the regional geologic setting of Petrified Forest National Park.

Purpose of the Geologic Resources Inventory 

The Geologic Resources Inventory (GRI) is one of 12 

inventories funded by the National Park Service (NPS) 

Inventory and Monitoring Program. The GRI, 

administered by the Geologic Resources Division of the 

Natural Resource Program Center, is designed to 

provide and enhance baseline information available to 

park managers. The GRI team relies heavily on 

partnerships with institutions such as the U.S. Geological 

Survey, Colorado State University, state geologic surveys, 

local museums, and universities in developing GRI 

products.

The goals of the GRI are to increase understanding of the 

geologic processes at work in parks and to provide sound 

geologic information for use in park decision making. 

Sound park stewardship requires an understanding of 

the natural resources and their role in the ecosystem. 

Park ecosystems are fundamentally shaped by geology. 

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 these goals, the GRI team is systematically 

conducting a scoping meeting for each of the 270 

identified natural area parks and providing a parkspecific 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 Geographic 

Information Systems (GIS) Data Model. These digital 

data sets bring an interactive dimension to traditional 

paper maps. The digital data sets provide geologic data 

for use in park GIS and facilitate the incorporation of 

geologic considerations into a wide range of resource 

management applications. The newest maps contain 

interactive help files. This geologic report assists park 

managers in the use of the map and provides 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/).

Park Setting

Humans have inhabited the Petrified Forest National 

Park (fig. 1) area for at least 13,000 years (National Park 

Service 2010). Prehistoric peoples created a variety of 

legends regarding the petrified-wood deposits in the 

area. For example, the southern Utah Paiute interpreted 

petrified logs to be the arrow shafts of their thunder god 

Shinuav while the Navajo believed the logs represented 

the monster Yietso, slain by Navajo ancestors (Mayor 

2005; National Park Service 2010). In addition to 

incorporating the fossil resources into their legends and 

culture, prehistoric peoples used petrified wood as

building material (fig. 2) and for making projectile points 

(fig. 3).

The first Euro-Americans (Spaniards) passed through 

the Petrified Forest National Park area of Arizona in 

1540; however, it wasn’t until the mid-1800s that the area 

received recognition as a result of a U.S. Army survey 

report of trees that had turned to stone. After examining 

the area in 1899, U.S. Geological Survey (USGS)

paleontologist Lester F. Ward recommended that 

homesteaders no longer be allowed to claim land in this 

area. This recommendation and the growing excitement 

over the area’s scenic and scientific values spurred the 

General Land Office to withdraw the area from 

homestead entry. However, the petrified forests 

remained vulnerable to wood theft, which reached 

alarming proportions with the completion of the 

railroads in this area (National Park Service 1990). 

Railroad passengers would take excursions from a 

coaling and watering stop in nearby Adamana, Arizona,

to “Chalcedony Park,” as the area was then known. 

These collectors would load railroad boxcars with 

petrified wood for shipment to eastern states for the 

manufacturing of table tops, mantel pieces, and other 

ornaments. In a short time, collectors and souvenir 

hunters had hauled off tons of petrified wood, as well as 

quartz crystals and American Indian artifacts. In 1906, a 

huge rock crusher threatened to pulverize petrified logs 

from the area for the manufacturing of abrasives. On 

December 8, 1906, President Theodore Roosevelt (who, 

three months earlier, had signed An Act for the 

Preservation of American Antiquities) proclaimed the

Petrified Forest as a National Monument to curtail the 

alarming rate at which wood was disappearing from the 

area. Petrified Forest National Monument became the 

first “fossil park” in the National Park System, giving the 

National Park Service stewardship over 24,596 ha 

(60,776 ac) of petrified wood sites.

Over the years, numerous changes have occurred to the 

boundaries of the monument (fig. 1). In 1962, the U.S. 

Congress redesignated the monument as Petrified Forest 

National Park. In 1970, as a result of the Wilderness Act 

of 1964, 20,340 ha (50,260 ac) of parkland were set aside 
2 NPS Geologic Resources Division

as wilderness. This area, along with a portion of Craters 

of the Moon National Monument (Idaho), became the 

first wilderness areas in the National Park System 

(National Park Service 2000). In December 2004, the size 

of the authorized boundary of Petrified Forest National 

Park more than doubled; this expansion included the 

West Rim of the Painted Desert. While the top two 

priorities for addition of lands to the park in 2004 were 

preserving paleontological and archaeological resources, 

the boundary change also protects the very important 

“first view” of the Painted Desert, which visitors see 

when approaching the park from the west on Interstate 

40 (I-40) (National Park Service 2006).

Before I-40 ushered in visitors, Petrified Forest National 

Park was crossed by the old 35th Parallel Route, the 

railroad (presently the Burlington Northern Santa Fe 

Railway), and Route 66. These routes followed the lay of 

the land in the low-gradient Puerco River valley. Federal 

government surveyors charted a course for a possible 

cross-country railroad line in December 1853. Managers 

of the Atlantic & Pacific Railroad chose this route, 

completing tracks through northern Arizona in 1882. 

Route 66, the famed “Mother Road,” paralleled the same 

route and opened the region to auto travelers in the 

1930s (Houk 2005).

Colorado Plateau

The Petrified Forest is part of the Colorado Plateau 

physiographic province—a high-elevation region of 

basins, plateaus, and canyons, roughly centered on the 

Four Corners area of Colorado, New Mexico, Utah, and 

Arizona (fig. 4). The uplift that elevated the plateau is a 

relatively recent geologic event, occurring within the past 

70 million years. Numerous National Park System units 

are situated on the Colorado Plateau. The Uinta 

Mountains of Utah and the Rocky Mountains of 

Colorado define the northern and northeastern 

boundaries of the plateau. The Mogollon Rim—an 

erosional cuesta that separates the Colorado Plateau 

from the extensively faulted Basin and Range 

physiographic province—marks the southern boundary. 

The Rio Grande Rift Valley in New Mexico defines the 

eastern boundary. A broad transition zone—where 

geologic features typical of Colorado Plateau and Basin 

and Range comingle—lies to the west. 

Globally Significant Upper Triassic Exposures

The lack of overburden in the park provides excellent 

exposures, making these Triassic deposits (about 220 to 

200 million years old) some of the most accessible for 

study. Furthermore, the Petrified Forest National Park 

Expansion Act of 2004 added 26 km (16 mi) of the 35-km 

(22-mi) Chinle escarpment, which contains the world’s 

most significant record of fossils from the Upper Triassic 

Period. The petrified logs were always considered 

beautiful and technically interesting, but scientists now 

realize that the scenic and scientific values greatly exceed 

a “collection of curiosities,” as they were once viewed by 

visitors. Today, this resource is known to be part of an 

ancient ecosystem that represents an especially 

significant time in the evolution of life on Earth—a time 

of transition when the earliest dinosaurs evolved 

(National Park Service 1990). Scientists are able to relate 

the fossils to their environment of deposition, further 

enhancing their scientific value. These fossils are of 

particular interest because few Upper Triassic terrestrial 

fossils are known, and the concentration of so many 

representatives of an ancient ecosystem in such a small 

area is rare.
PEFO Geologic Resources Inventory Report 3

Figure 2. Agate House Pueblo. Ancestral Puebloan peoples from the Pueblo III period (between about 1150 and 1300 CE [Common Era; 

preferred to “AD”]) built the structure from petrified logs. The Civilian Conservation Corps partially reconstructed Agate House in 1934. 

National Park Service photograph.

Figure 3. Petrified wood projectile points. Prehistoric peoples utilized the abundant petrified wood of the Petrified Forest region as raw 

material for projectile points. Not to same scale. National Park Service photographs by T. Scott Williams.
4 NPS Geologic Resources Division

Figure 4. Colorado Plateau. Among many other National Park System units, Petrified Forest National Park is situated on the Colorado 

Plateau. This region of high elevation composes the Four Corners area of Utah, Colorado, Arizona, and New Mexico. The green areas on 

the figure represent National Park System units, a small selection of which are labeled. Shaded relief imagery compiled by Jason 

Kenworthy (NPS Geologic Resources Division) from ESRI Arc Image Service, ESRI World Shaded Relief.
PEFO Geologic Resources Inventory Report 5

Geologic Issues

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

Petrified Forest National Park on June 27–28, 2001, 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. Contact the Geologic Resources Division for 

technical assistance.

Participants of the 2001 GRI scoping session identified 

two main resource management concerns for Petrified 

Forest National Park: (1) resource theft, specifically with 

regard to petrified wood; and (2) bentonitic (swelling)

soils. According to the scoping summary, “currently, the 

greatest issue facing park resource management is 

dealing with the threat of resource theft, as tons of 

petrified wood are stolen from the park on a yearly 

basis.” Thus, the digital geologic map for the park was

produced at a higher resolution (scale of 1:24,000 rather 

than 1:48,000) to “aid in defining areas at highest risk to 

resource theft” (see Map Unit Properties section and 

Appendix A). Note the map was produced prior to the 

2004 boundary expansion.

Based on the results of the scoping meeting, 

paleontological resources and bentonite are prioritized 

are discussed first in this section. Discussions of other 

issues of possible concern for resource managers follow. 

Petrified Wood

Aptly named and simply stated, Petrified Forest National 

Park was set aside to preserve one of the Earth’s largest 

and most colorful concentrations of petrified wood

(fig. 5). Recent research has shown the significance of the 

fossilized wood in its paleoenvironmental context

(revealing the evolutionary histories of Triassic plants 

and animals), validating one of the primary purposes of 

park management: the protection of the petrified wood.

Over the years, attitudes about the protection of petrified 

wood have evolved: the earliest caretakers of the 

monument were allowed to sell the pieces of the colorful 

resource to supplement their $1 per year “salaries” 

(National Park Service 1990) Today, the park has a “zero 

tolerance” policy with regard to the illegal collection of 

petrified wood (Bill Parker, Petrified Forest National 

Park, e-mail, October 29, 2008). Nevertheless, since the 

petrified forests were first recognized and appreciated, it 

has been a known fact that petrified wood disappears at 

the hands of collectors—piece-by-piece or by the ton. As 

stated in Petrified Forest Natural and Cultural Resources 

Management Plan and Program (National Park Service

1986), “visitors annually remove approximately 12 tons 

of petrified wood from the park” (p. 3). This anecdotal 

12-ton amount has been woven into the fabric of the 

park’s resource identity, but its empirical validity has yet 

to be proven (Bill Parker, Petrified Forest National Park, 

e-mail, October 29, 2008). Through the years,

investigators have undertaken studies to estimate the 

amount of petrified wood removed from the park. In 

1990, investigators used 45 “baited plots” along visitor 

pathways and suggested that visitors stole 8,129 pounds 

[4.065 tons] of petrified wood per day (Scher 1990). 

Furthermore, this study estimated that 1.01 pounds of 

petrified wood were stolen per person and 2.73 pounds 

of petrified wood were stolen per car. Also, for every 416 

pounds of wood stolen, one pound was recovered (Scher 

1990). The wood samples in the baited plots were near 

gem quality (and presumably harder to resist). Wood 

previously confiscated from vehicle inspection stations

was used in the baited plots. Another study observed 

visitor behavior at Long Logs and Crystal Forest, two 

popular petrified wood sites. During this 1993 study, 

investigators observed 125 people stealing petrified 

wood over 122 hours of observation (Roggenbuck et al. 

1997). This rate averages about 1.02 thieves per hour 

(Roggenbuck et al. 1997).

These widely varying findings lead to questionable 

estimates and make quantitative analysis of the issue

difficult. However, the consensus is that too many 

people are unable to resist the pocketing of a park

“souvenir” in the form of a small piece of petrified wood.

The park’s history is replete with programs aimed at 

minimizing the pilfering of petrified wood by souvenir 

collectors (Monkevich et al. 1994; Roggenbuck et al. 

1997). Through the years, park managers have tried 

various methods to prevent the loss of this resource. For 

example, small souvenir-sized pieces of petrified wood 

were purchased from outside sources and given to 

visitors as an incentive to prevent them from 

“shoplifting” souvenir chips from the park. Studies have 

shown that both written materials and personal contacts 

are effective in gaining visitor compliance (Roggenbuck 

et al. 1997; Widner and Roggenbuck 2000; Attarian 

2003). Therefore, an intensive signing program was 

instituted to inform visitors that no more of the resource 

was being made, so they should leave it for future 

generations to enjoy. Employees both in and out of 

uniform have been stationed at potential theft sites to try 

to prevent or reduce theft (National Park Service 1986). 

National Park Service Management Policies 2006 states, 

“The sale of original paleontological specimens is 

prohibited in parks” (National Park Service 2006b, p. 55). 

However, this policy is waived for Petrified Forest 

National Park because research suggests that banning 

wood sales in park gift shops could lead to an increase in 

wood theft (National Park Service 2006a). Park managers 

require that park concessionaire makes buyers aware 
6 NPS Geologic Resources Division

that the wood being sold is not collected from within the 

park. Roggenbuck et al. (1997) found that 65.5% of 

visitors surveyed strongly agreed that being able to buy 

petrified wood in the park gift shops reduced the 

temptation to take a piece from park grounds. 

Roggenbuck et al. (1997) made a number of 

recommendations for reducing fossil theft within the 

park. A variety of print, web-based, and on-the-ground 

interpretation techniques maximizes the potential to 

educate visitors regarding park regulations and the 

stewardship mission of the NPS. For example, the 

researchers found that the park brochure was the most 

used informational document for learning about the 

park’s rules and regulations (76% of the visitors 

surveyed). Web-based outreach could reach visitors 

prior to their travels to the park. 

The issue is also addressed in the form of a children’s 

story, The Tourist, the Park Ranger, and the Petrified 

Forest, at http://www.nps.gov/archive/pefo/Story/

story_titlepage.htm (accessed November 13, 2009). This 

tale discusses the consequences of theft and promotes 

moral reasoning and change in behavior. 

Petrified Forest National Park was highlighted on the 

Park Spotlight page of the NPS Web site at 

http://www.nps.gov/parkoftheweek/pefo.htm (accessed 

November 13, 2009). At the end of the text is a list of 

NPS priorities that clearly state the concern about 

resource theft, including petrified wood: 

Resource Theft: Everything in a national park is 

referred to as resources, including the plants, animals, 

geological formations, archaeological artifacts, and 

even the air. Resource theft is a continuing problem for 

the park. Each year several tons of petrified wood is 

stolen. Many areas have been stripped clean of small, 

easily removed pieces. Visitors also pilfer other 

minerals and cultural artifacts (pottery shards, 

arrowheads) from park sites. 

Park staff work very hard to slow the theft of resources 

through strict enforcement of park regulations via 

fines or arrest. Staff also educates the visiting public 

about the significance of the environment and the 

irreplaceable information it contains. Park 

publications, displays and exhibits are designed to 

increase visitor awareness of these resources, leading 

to a stewardship ethic and desire to protect Petrified 

Forest National Park for these and future generations. 

Petrified Wood Collection within the Expanded Boundary

Most of the sizable logs have been removed from land 

acquired as part of the 2004 boundary expansion 

(National Park Service 2008a). Although collection of 

petrified wood is prohibited on federal and unleased 

state lands in Arizona, removal is legal on private lands 

within the expanded boundary of Petrified Forest 

National Park with the permission of the owners. 

Extraction of petrified wood and associated impacts 

could occur on nearly 32,000 ha (80,000 ac) of privatelyowned lands within the expanded boundary (National 

Park Service 2008a).

Because of the “disappearance” of petrified wood at the 

surface of the expanded parklands, future recovery will 

involve more intrusive techniques that literally move into 

the realm of mining. A common technique involves 

removal with a ripper hook, which typically extends 1.8 

to 3 m (6 to 10 ft) into the ground. As a bulldozer 

crisscrosses an area, the attached hook snags objects 

such as buried petrified logs or root balls. An excavator 

or backhoe is utilized to dig out the specimens (National 

Park Service 2008a). 

Paleontological Resource Damage

Although preserved for more than 200 million years, time 

is taking its toll on the fossils at Petrified Forest National 

Park. The lack of vegetation, nature of the strata, and 

geomorphic character of the badlands continuously 

subject the park’s paleontological resources to erosion. 

Natural weathering processes can start to damage fossils 

even before they are actually exposed, and once these 

resources are at the surface, they are quickly destroyed, 

often losing much of their scientific value for correlation, 

evolution, and understanding of past depositional 

environments. Active management—including location 

surveys, preparation, and placement in a museum 

collection for preservation and study—is the key to fossil 

preservation. 

Second only to erosion, “poor science” is another factor 

in fossil preservation. The ongoing paleontological 

resource inventory at Petrified Forest National Park has 

revealed that some damage to vertebrate fossil resources 

is the result of poor science being conducted by 

permitted researchers (Parker and Dorn 2006). Examples 

of poor science include partially excavated, abandoned 

specimens that are later destroyed by exposure;

improperly prepared or heavily damaged specimens;

specimens collected without clear research plans or 

proper documentation; and undocumented specimens 

collected by untrained workers of scientists with permits.

The National Park Service has compiled various 

guidance documents to help resource managers avoid 

damage to paleontological resources, in particular, 

Natural Resource Management Reference Manual 77, 

formerly Director’s Order 77 (National Park Service 

2004b). In addition, the Geological Society of America 

published a manual for monitoring geologic resources, 

which includes a chapter on paleontology (Santucci et al. 

2009). The monitoring strategy suggests the following 

five vital signs for paleontological resources. Because 

paleontological localities vary widely from location to 

location within a park and throughout the National Park 

System, any specific vital sign might not be useful or 

appropriate at all fossil sites.

Rates of Natural Erosion (Geologic Variables)

This vital sign assesses the geologic variables that 

contribute to increased erosion at a locality such as 

physical characteristics of a rock unit (e.g., rock type, 

hardness, and cementation), bedding, degree of slope, 
PEFO Geologic Resources Inventory Report 7

and geochemistry. As mentioned above, natural 

erosional processes, quickly impact fossils exposed at the 

surface within the badlands landscape of the park. This 

indicator allows the researcher to assess data on annual 

precipitation, rainfall intensity, relative humidity, wind 

speed, and freeze-thaw index (number of 24-hour 

periods per year when temperature fluctuates above and 

below 0°C [32°F]).

Rates of Natural Erosion (Climatic Variables)

This vital sign assesses local climatic data on annual 

precipitation, rainfall intensity, relative humidity, wind 

speed, and freeze-thaw index. Rainfall during intense 

summer afternoon thunderstorms at the park increase 

erosion of the badlands within Petrified Forest National 

Park.

Catastrophic Geologic Processes or Geohazards

This vital sign assesses the potential for catastrophic 

geologic processes or geohazards that could impact a 

fossil locality. Such processes include volcanism, 

geothermal activity, earthquakes, glacial activity, and 

mass-wasting events (e.g., landslides, slumps, and 

rockfalls). Any of these types of mass-wasting events 

could damage fossil resources at Petrified Forest 

National Park (see Mass Wasting section).

Hydrology and Bathymetry

This vital sign assesses potential impacts to fossils near 

water bodies, where changes in water level can affect the 

stability of paleontological resources. Such changes 

could be caused by natural fluctuations in water level or 

be related to storm events and flooding. Flash floods are

a potential threat to fossils within the park.

Human Impacts

This vital sign assesses the potential for both intentional 

and unintentional human impacts on fossil resources. As 

noted above, humans are a primary threat to fossil 

resources within the park as a result of theft, vandalism,

and poor science.

Paleontological Resource Inventory

In 2001, resource managers at Petrified Forest National 

Park began to relocate and document all known 

paleontological sites within the park, beginning with 

those containing known vertebrate fossils (Parker 2003). 

As part of the ongoing inventory, investigators document 

the sites using the following three methods: (1) plotting 

with global positioning systems, (2) recording the 

physical description, and (3) photographing the site. This 

field inventory involves monitoring known fossil sites, 

collecting locality data, tying archival and collection 

information to fossil sites, and collecting representative 

specimens for park collections (National Park Service 

2004a). Park staff also assisted with the Petrified Forest 

section of a literature-based inventory for the entire 

Southern Colorado Plateau Network (Tweet et al. 2009). 

Although scientists and the public have been aware of the 

area’s rich fossil resources for more than 150 years, the 

inventory has underscored the incredible paleontological 

wealth at Petrified Forest National Park. By 2004, 

investigators had found 50 new vertebrate sites. 

Although all of the specimens found during the 

inventory are scientifically important, the skeleton of a 

large extinct crocodile-like aetosaur (Stagonolepis 

wellesi)—the second most complete aetosaur skeleton 

recovered from the Triassic of Arizona—was the most 

notable find of 2003 (Parker 2003). Discoveries in 2004 

surpassed even this aetosaur specimen. In the Painted 

Desert area of the park, the Revueltosaurus quarry 

yielded a dozen skeletons of the pseudosuchian 

archosaur Revueltosaurus callenderi. Revueltosaurus was 

previously only known from its teeth. Thought to 

represent an early ornithischian dinosaur, examination 

of this specimen showed that this animal is more closely 

related to crocodiles, which has important implications 

for the global fossil record of early dinosaurs (Parker et 

al. 2005). Many other significant finds of vertebrate 

material (table 1) have resulted in numerous publications 

(see Paleontological Research section) and have 

identified Petrified Forest National Park as the locale to 

study the “dawn of dinosaurs” (Long and Padian 1986; 

Hunt et al. 2002).

Table 1. Discoveries of significant vertebrate fossils at 

Petrified Forest National Park.

Year Fossils

2001 Partial skeleton of aetosaur Calyptosuchus 

wellesi

2002 Phytosaur skeleton, armor plates from a new 

species of aetosaur, skull roof of new species of 

phytosaur, partial skeleton of the 

crocodylomorph Parrishia

2003 Complete phytosaur (Leptosuchus crosbiensis) 

skull, plates from an aetosaur Rioarribasuchus

chamaensis, previously known only from New 

Mexico; the first recorded jaw material of 

Trilophosaurus ever found in the park; a partial 

skeleton of the rare enigmatic reptile Vancleavea

2004 A dozen skeletons of the pseudosuchian 

archosaur Revueltosaurus callenderi; new species 

of aetosaur; remains of rauisuchians, aetosaurs, 

phytosaurs, lungfish, and dinosaurs

2005 Well-preserved phytosaur skull; Revueltosaurus

skeleton; material from metoposaurs, aetosaurs, 

and phytosaurs

2006 Revueltosaurus skeleton; theropod, rauisuchian, 

and crocodylomorph material

2007 Phytosaur skull; aetosaur partial skeleton, 

including skull

2008 Five new phytosaur skulls, Poposaurus pelvis, 

metoposaur skulls

2009 Phytosaur skull, aetosaur partial skeleton

Sources: http://www.nps.gov/pefo/naturescience/research-activities.htm

(accessed November 13, 2009); Bill Parker (Petrified Forest National Park), 

written communication, August 2009.

Future phases of the field inventory will include 

documentation of localities with plant, invertebrate, and 

trace fossils. According to the park’s strategic plan (2005–

2008), the park hosts a total of 555 documented sites. 

More than 200 of these have been relocated as a result of 

the inventory. However, efforts to find the remaining 

sites could be difficult due to the lack of specific 
8 NPS Geologic Resources Division

information contained in past researchers’ field notes. 

Nevertheless, park staff will make every effort to reach 

the goal of finding all documented sites (National Park 

Service 2005a). 

As identified in the park’s resources management plan 

(National Park Service 1994) and the foundation for 

planning and management (National Park Service 

2006a), there is a need for more staff and trained 

volunteers to inventory and monitor fossil resources, 

which have been stretched even thinner as a result of the 

boundary expansion. 

Paleontological Research

In 1936, Charles Newton Gould stated in his report as 

regional geologist, “Petrified Forest is so well known, 

and the geology so thoroughly understood that it is 

unnecessary at this time to do little more than call 

attention to some of the more outstanding features”

(p. 1). Presumably, Gould soon realized his error because 

immediate, more extensive reports followed in 1937 and 

1938. In 1935, the National Park Service hired the 66-

year-old Gould out of his “retirement” to oversee an 

eight-state region in the West and Southwest. For the 

next five years, Gould advised the NPS on water 

resources, road construction, and future expansion. 

Before working as regional geologist, Gould had served 

as the first director of the Oklahoma Geological Survey 

and as a consulting geologist for the petroleum industry 

(Weaver 2007). 

Today, what is not known about the geology of the park 

greatly exceeds what is known, and excitement grows 

with each new discovery (National Park Service 1990). 

Research has revealed that the park’s strata document 

“the dawn of the dinosaurs” perhaps better than 

anywhere else in the world. By the Upper Triassic, the 

first dinosaurs were just beginning to appear, and some 

of the earliest dinosaur fossils known are from Petrified 

Forest National Park. In addition, mammals appeared 

during the Triassic, and many paleontologists now 

consider the Triassic as the time when modern 

ecosystems were being established. The rich associations 

of Triassic plant and animal fossils in the park promise to 

contain a comprehensive record of this time of 

transition. Petrified Forest National Park is becoming a 

standard (leading locality) for studying Upper Triassic 

terrestrial systems globally (Bill Parker, Petrified Forest 

National Park, e-mail, October 10, 2008). 

Since 2000, park and cooperating paleontologists have 

published more than 40 papers about the park’s 

paleontological resources—particularly, fossil 

vertebrates, but also fossil plants and microinvertebrates 

(http://www.nps.gov/pefo/naturescience/publishedresearch.htm; accessed November 13, 2009). According 

to park paleontologist Bill Parker, “Everything we 

thought we knew is changing and we are finally getting 

closer to understanding the geological and 

paleontological story here” (Bill Parker, Petrified Forest 

National Park, e-mail, October 10, 2008). Even new 

evidence about the petrified trees is emerging (Savidge 

2007). 

The Petrified Forest National Park area has been a 

paleontological research laboratory for more than 150 

years. Although outside researchers’ projects might not 

necessarily be identified as a resource management 

priority, the findings can still be valuable for park 

science, interpretation, management, and planning. 

Researchers provide copies of field data (e.g., notes, 

photographs, and maps) to park managers. Researchers 

also submit an investigator’s annual report (National 

Park Service 2004b). Scientists from outside institutions 

who request and receive research permits accomplish 

much paleontological study that result in significant 

findings. The permitting system includes provisions to 

ensure that scientific research activities comply with 

both Servicewide and park-specific requirements 

(National Park Service 2004b). 

An analysis of fundamental resources and values 

identified the need for suitable space to conduct 

laboratory, office, and collection activities for on-site 

research. The lack of space for researchers could inhibit 

valuable research and lead to the inability to attract top 

scientists to Petrified Forest National Park (National 

Park Service 2006a).

Revisions to Stratigraphy

The stratigraphic nomenclature at Petrified Forest 

National Park has been undergoing revisions since the 

early 1990s. Most recently, investigators have 

reevaluated the Sonsela Member of the Chile Formation 

(Martz and Parker 2010) (table 2). The bulk of this effort 

was devoted to carefully examining exposures in the 

southern region of the park (Martz and Parker 2010). 

The Sonsela Member represents a transition from a 

predominantly muddy unit (mudstone) dominated by 

overbank deposits to a predominantly sandy unit 

(sandstone) dominated by channel deposits. This unit 

also contains an abrupt faunal overturn of the most 

common vertebrate fossils in the park, phytosaurs and 

metoposaurs (see Paleontological Resources section 

under “Geologic Features and Processes”). 

Over the years, investigators have separated, combined, 

translated, and renamed various portions of the Chinle 

Formation and even elevated it to group status (Lucas 

1993). More reorganization is likely while detailed 

geologic mapping is ongoing. At present, the accepted 

terminology for the members of the Chinle Formation is 

as follows (from oldest to youngest): Mesa Redondo, 

Blue Mesa, Sonsela, Petrified Forest, and Owl Rock. An 

unconformity separates the Chinle Formation from the 

overlying Bidahochi Formation (Miocene/Pliocene) (see 

the Unconformities section under “Geologic Features 

and Processes”). Unnamed and undifferentiated 

Quaternary (Pleistocene and Holocene) rocks and 

sediments, as well as eolian dunes and sand sheets, top 

the sequence at the park (Blakey and Raucci 2006; Parker 

2006; Woody 2006). The current “working stratigraphy” 

varies slightly from the digital geologic map produced in 

2006 (see “Map Unit Properties” section and Appendix 

A).
PEFO Geologic Resources Inventory Report 9

Correlation of strata at the park has been contentious. In 

the early 1990s, 50 lithographic terms were applied to 

Upper Triassic nonmarine strata in the western United 

States, and the Chinle “Group” encompassed 27 

formational names in nine states (Lucas 1993). A major 

problem in the park is relating the members of the Chinle 

Formation between the northern and southern portions. 

Approximately 6 km (4 mi) of Cenozoic alluvium covers 

the Puerco River area, which splits the park in half. Thus, 

beds so distinctive to the north and south have limited 

exposures across the park (Murry and Long 1989; Murry 

1990). Martz and Parker (2010) demonstrate the 

importance of geologic mapping, “walking the contacts,” 

and thoroughly documenting measured sections when 

constructing lithostratigraphic interpretations of the 

Chinle Formation in Petrified Forest National Park.

To further complicate matters, the exact age of the 

Chinle Formation is uncertain. The formation is known 

to be Upper (Late) Triassic, but scientists are currently 

scrutinizing the isotopic age of this geologic period 

(Walker and Geissman 2009a). The International 

Commission on Stratigraphy (2009) placed the age of the 

Upper Triassic at approximately 228.7 to 199.6 million 

years ago. However, the Geological Society of America 

brackets the same period as 228 to 201.6 million years 

ago (Walker and Geissman 2009b). 

Table 2. Revised stratigraphy of the Chinle Formation. Refer 

to fig. 3 in Martz and Parker (2010) for previous 

interpretations and nomenclature for the Chinle Formation 

in the southern part of Petrified Forest NP.

“Fm” = Formation.

Fm Member Bed Chinle Formation

Petrified Forest Member

Flattops Bed 4

Flattop Bed 3

Flattop Bed 2

Sonsela Member

Martha’s Butte beds

Jim Camp Wash beds

Jasper Forest /

Rainbow Forest Bed

Lot’s Wife beds

Camp Butte beds

Blue Mesa Member Newspaper Rock Bed

Mesa Redondo Member

 Source: Martz and Parker (2010).

Investigators of Chinle stratigraphy have not pinpointed 

the upper or lower boundaries of the formation; 

however, the top of the Chinle Formation is known to 

predate the Triassic-Jurassic boundary, which is in the 

overlying Wingate Sandstone (Lucas et al. 1997, 2005). 

Riggs et al. (2003) and Heckert et al. (2009) obtained 

maximum ages of 213 ± 1.7 million years and 211 ± 0.7 

million years respectively for the Black Forest Bed, near 

the top of the Petrified Forest Member. The base of the 

Chinle Formation is marked by the Mesa Redondo 

Member, which comprises the oldest and 

stratigraphically lowest rocks at Petrified Forest National 

Park. Unfortunately, the Mesa Redondo Member is 

exposed only in the Tepees area of the park (Parker and 

Irmis 2005). However, the base of the overlying Blue 

Mesa Member is known to be about 219 million years 

old (Irmis and Mundil 2008; Mundil and Irmis 2008); 

therefore, the Mesa Redondo Member must be older. 

Bentonite

The picturesque beds of the Chinle Formation shape the 

beautiful badlands of the park. They also create 

hazardous conditions. The purple, pink, gray, yellow, 

brown, and red mudstone beds in the Owl Rock, 

Petrified Forest, Sonsela, and Blue Mesa members 

contain altered volcanic ash called bentonite, which 

swells when wet and shrinks when dry, creating unstable 

foundations upon which to build infrastructure. Due to 

the high bentonitic content of the deposits, the surface 

absorbs moisture and expands, becoming sticky mud in 

flat areas and slumps on slopes. During heavy rainfalls, 

the mud on steep slopes collects in pellets that roll down 

into the stream channels where they disintegrate and are 

rapidly carried away as suspended material (Camp 1930). 

As the bentonite-rich deposits dry out between rainfall 

events, shrinkage cracks form (fig. 6). Some cracks, called 

“pipes,” can penetrate deeply below the surface. When 

rainfall returns, much of the water falling onto the 

surface enters these cracks, moves through the pipes, and 

reappears at lower levels in the gullies. Gradually, the 

partly weathered, friable surface material is carried 

through the subsurface by this “piping” process. 

Sinkholes form at the surface as a result of piping. The 

sinkholes vary from a few inches deep to as much as 3 m 

(10 ft), making mere dimple depressions to basins 5 to

6 m (15 or 20 ft) across (Malott 1939). Piping also 

undermines slopes that later collapse. In some places, 

natural bridges can span the subterranean pipes before 

collapsing (Bezy and Trevena 2000). New slope profiles 

and sinkholes can develop in a few hours when flash 

floods occur (Harris and Tuttle 1990). Piping can be a 

major management issue in anthropogenic areas such as 

earthen dams and raised roads (Pete Biggam, NPS soil 

scientist, e-mail, February 23, 2007). 

Scoping participants identified numerous problems with 

bentonitic clays in the park. For example, the Painted 

Desert Inn located in the northern portion of the park 

has experienced moderate to severe cracking in both 

exterior and interior walls, as well as movement in floor 

slabs (Dee 1992). Historic buildings in the southern 

portion of the park are not as susceptible to bentonite 

problems because they are built on fill and sandstone 

material. In addition, the presence of bentonite threatens 

the integrity of roads and trails. Bentonite underlies 

significant portions of the mainline road (Denver Service 

Center 1978), and scoping participants identified the 

Blue Mesa Trail as requiring geotechnical surveys 

because of bentonite problems. 

In 2005, in cooperation with the University of Arizona, 

the National Park Service published Maintenance Guides 

for the Treatment of Historic Properties, Petrified Forest 

National Park (Gorski and Lovato 2005). This 

publication includes recommendations for drainage 

systems in bentonitic clays, suggesting that water should 

be transported as far away as possible from building 
10 NPS Geologic Resources Division

foundations. In addition, the authors suggest that park 

managers consider water harvesting as a conservation 

measure and to keep water away from buildings (Gorski 

and Lovato 2005).

Mass Wasting

Mass wasting in Petrified Forest National Park is 

primarily a result of the downslope movement of 

mudstone in the Chinle Formation. The mudstone 

contains water-absorbing (expandable) bentonite clay. 

During summer rain events, the clay absorbs water and 

the mudstone becomes “plastic.” Gravity then pulls the 

water-saturated mudstone layers downslope, forming 

“slumpage terraces” (fig. 7) (Bezy and Trevena 2000).

Along the cliffs near Pintado Point is a slump block. The 

plateau is capped by resistant basalt of the Bidahochi 

Formation but is underlain by softer clay. This caprockover-clay scenario sets up the potential for mass wasting. 

When saturated, the clay loses its supportive strength 

and causes blocks of caprock to break off, slide 

downslope, and rotate backward. This process called 

“slumping” tremendously increases the rate of cliff 

retreat and valley-widening in the Southwest (Bezy and 

Trevena 2000).

The Newspaper Rock overlook displays the process of 

cliff retreat. Caps of the Newspaper Rock Bed of the 

Chinle Formation are prone to cliff retreat when 

“supported” by mudstone. Rain and meltwater erode the 

underlying mudstone, widening fractures in the 

Newspaper Rock Bed, and ultimately causing slabs of 

rock to break off and topple to the slopes below (fig. 8). 

In 1984, the trail that once descended to Newspaper 

Rock was destroyed by the movement of large sandstone 

slabs (Bezy and Trevena 2000). The Blue Mesa cliff is also 

experiencing cliff retreat (Bill Parker, Petrified Forest 

National Park, written communication, June 2009).

As highlighted in Guide to Geologic Features at Petrified 

Forest National Park (Bezy and Trevena 2000), these 

features of mass wasting can be of interest to park 

visitors. Such features also can require attention and 

mitigation by resource managers. Wieczorek and Snyder 

(2009) offer background information and vital signs for 

monitoring mass wasting. 

Blakey and Raucci (2006) included colluvium as part of 

undifferentiated surficial deposits (Qsu) on the geologic 

map of the park. These deposits indicate areas of future 

susceptibility to mass wasting. Preliminary Map of 

Selected Mass Movement Events in Arizona (Realmuto 

1985) showed a 1984 rock slide event that occurred in 

the park (T18N R24E), which cost $25,000 to mitigate. In 

1985, Howard J. Haiges of the Denver Service Center 

conducted a geotechnical survey (and submitted a 

technical report to the regional director of the Western 

Regional Office) concerning an earth flow that had 

developed adjacent to Newspaper Rock (Haiges 1985). 

Only when such phenomena conflict with infrastructure, 

visitation, or cultural resources do they constitute a 

serious problem or hazard. The severity of such 

problems is directly related to the extent of development 

in the affected areas. Early recognition, avoidance, and 

corrective engineering can mitigate adverse effects 

(Rogers et al. 1974).

Subsidence

In 2005, park staff requested assistance from the 

Geologic Resources Division in evaluating a subsidence 

crack at the Blue Mesa Loop Road and the mesa edge 

(National Park Service 2005b). Although GRD staff 

deemed the crack relatively benign and park 

maintenance personnel repaired the road damage, this 

example illustrates the potential for subsidence to affect 

park infrastructure. According to Rogers et al. (1974), 

ground subsidence is “characterized by downward 

displacement of surface material by natural phenomena 

such as removal of underground fluids, natural 

consolidation, or dissolution of underground minerals, 

or by man-made phenomena such as underground

mining” (p. 61).

On a larger scale, subsidence creates topographic 

features on the landscape. Colpitts (1996) reported a 

possible solution-collapse depression—Blue Mesa sink—

in Petrified Forest National Park. Situated 12 km (8 mi) 

south of I-40, this semicircular collapse feature is 1 km 

(0.6 mi) in diameter with surface relief of about 30 m (100 

ft). Sandstones of the Blue Mesa Member dip radially 

into the central depression at angles ranging from 5° to 

15°. Colpitts (1996) proposed that the collapse structure 

is related to evaporate dissolution of halite and sylvite in 

the upper part of the underlying Schnebly Hill 

Formation (Permian); however, also of note is the 

underlying Permian Supai Formation, which contains 

halite and potash (see Potash section). Dissolution of 

halite or future underground mining of potash could 

cause subsidence of overlying strata.

Potash

Potash prices have skyrocketed. At the beginning of 

2008, potash went for about $200 per metric ton; at its 

summer high, it sold for $600 per metric ton. Despite the 

sharply declining trend in nearly every commodity in 

2008, potash prices held steady and even ticked upward 

(U.S. Geological Survey 2010). 

This trend has renewed mining interests in Arizona 

deposits. Potash, which is rich in potassium, is used 

primarily for fertilizer, but also for ceramics, glass, and 

soap. The increasing price of North American ethanol 

corn production and the global demand for foodstuffs 

are creating an increased potash demand (for fertilizer) 

(Helmer 2008). The area of interest for Arizona is the 

Holbrook Basin, a 1,550-km2 (600-mi2) salt deposit east 

of Holbrook, Arizona. This basin underlies a significant 

portion of Petrified Forest National Park (fig. 9). The 

potash is a component of the Permian Supai Formation 

(270 to 220 million years old) and not present at the 

surface. The salt appears to have formed by desiccation 

of saline mud flats and salt pans of an inner sabkha 

(supra-tidal environment in arid climates). According to 

Rauzi (2008a), the occurrence of potash near the top of 

the salt deposit is due to the relative solubility of potash 
PEFO Geologic Resources Inventory Report 11

and salt during the evaporation of seawater across the 

sabkha. Repeated incursions of seawater appear to have 

preferentially dissolved and re-precipitated the potash, 

thereby separating and concentrating the potassium 

from the halite.

Half of the deposit occurs under a combination of 

private, state trust, and Native American Tribal lands. 

The other half is beneath Petrified Forest National Park. 

Approximately 20% of the potash deposit is situated 

under the pre-2004 boundary, which is closed to mining. 

Another 30% of the deposit underlies lands that became 

part of the national park as a result of the Petrified Forest 

Expansion Act of 2004 (Conway 2008). The state owns 

more than 100 km2 (40 mi2) of land in the expanded area 

of the park. The state could issue leases on these lands. 

As a result, efforts to negotiate a land management 

agreement with the state over state lands in the expanded 

boundary may be more difficult than originally 

envisioned (National Park Service 2008a). 

According to Rauzi (2008a), “the location of the potash 

under [Petrified Forest National Park] will require a 

creative approach to full access and future development 

of Arizona’s strategic potash deposits” (p. 2). Because the 

potash deposit under and around the park lies mostly 

between 300 and 460 m (1,000 and 1,500 ft) below the 

surface, underground mining techniques such as room 

and pillar, longwall, cut and fill, and open stope could be 

used to exploit the deposit. This means that surface 

mining in the park could be avoided, thereby leaving the 

petrified wood resource intact (National Park Service 

2008a). “Using such techniques means that large areas 

can be mined from a single surface location that includes 

the main shaft, processing facilities, and storage and 

waste disposal areas. Though impacts can be centralized, 

the footprint may cover hundreds of acres” (National 

Park Service 2008a, p. 3). Furthermore, “while the nature 

of the mining might allow for flexibility in locating the 

surface works, it will not be possible to hide it given the 

local terrain” (National Park Service 2008a, p. 4). That is, 

the Holbrook deposit is roughly 50 km (30 mi) long and 

25 km (15 mi) wide, which could accommodate multiple 

work areas at the surface. The location of federal surface 

land and federally owned minerals would affect the 

underground mine layout and possibly the placement of 

surface works. 

Liquefied Petroleum Gas Storage

The extensive salt deposits of the Permian Supai 

Formation underlie about 9,100 km2 (3,500 mi2

) of eastcentral Arizona and attain a maximum thickness of 200 m 

(655 ft) (Rauzi 2000). Gas companies dissolve the salt 

(halite) and use the voids (caverns) to store liquefied 

petroleum gas (LPG). A storage cavern is created by 

drilling a hole and pumping freshwater into the opening 

through steel piping. The freshwater dissolves the salt, 

and the resulting brine is pumped out of the hole. Some 

brine is stored at the surface for later use, and some is 

pumped back into deep underground rock formations. 

The amount and direction of freshwater pumped into the 

hole determines the shape and size of the cavern (Rauzi 

2008a).

Eleven storage caverns, part of Ferrell Liquefied 

Petroleum Gas Storage Facility, are located 915 m

(3,000 ft) west of the park boundary along the Burlington 

Northern Santa Fe Railway, which services the facility. 

Rail tank cars transport the gas, which is pumped into the 

caverns during low demand. During periods of high 

demand, the gas is pumped from the wells and 

transported to market. These caverns do not underlie the 

park, however, and any expansion of the facility could be 

accomplished outside the park boundary (James C. 

Woods, Geologic Resources Division, written 

memorandum to superintendent, Petrified Forest 

National Park, December 4, 2000).

The top of the salt at the LPG storage facility is about 

275 m (900 ft) below the ground surface. The caverns are 

leached about 23 m (75 ft) below the top of the salt; they 

have an average radius of 18 m (60 ft) and height of 30 m 

(95 ft). Individual cavern volumes range from 26 to 42 

million L (7 to 11 million gal) (Rauzi 2008a). This facility 

began operations in 1971, and currently provides total 

storage for 318 million L (84 million gal) of butane and 

propane. In addition to the storage caverns, four large 

brine storage impoundments, four 18,000-gallon LPG 

tanks, two 30,000-gallon LPG tanks, pumping 

equipment, and associated piping are at the surface of the 

facility.

In 2000, the Geologic Resources Division conducted an 

assessment of the storage facility at the request of park 

staff. The Geologic Resources Division gathered most of 

the information from correspondence with Dale 

Thompson, the facility manager at Ferrell LPG Storage 

Facility, and Steve Rauzi, an oil and gas administrator for 

the Arizona Geological Survey. The assessment findings 

contain a description of the facility, a discussion of safety 

issues (e.g., evacuation for visitor safety in the event of a 

spill and the potential for spills from rail cars), 

recommendations, and conclusions (James C. Wood, 

Geologic Resources Division, written memorandum to 

superintendent, Petrified Forest National Park, 

December 4, 2000). In addition, the Geologic Resources 

Division prepared a document highlighting all mineral 

development in and adjacent to Petrified Forest National 

Park, including the LPG storage facility (National Park 

Service 2008a).

The following conclusions and recommendations from 

these two documents concern the management of 

geologic resources at Petrified Forest National Park:

• No significant potential for subsidence or sinkholes, 

which could impact the national park, are associated 

with the caverns.

• A catastrophic spill event at the Ferrell LPG Storage 

Facility would not likely impact park resources other 

than causing short-term degradation in air quality.

• The park superintendent should verify that he/she is 

on the storage facility’s emergency notification list for 

large-spill and fire incidences. In the event of a 

catastrophic spill or fire, evacuation and closure of the 

park road east of the storage facility might be 
12 NPS Geologic Resources Division

necessary to minimize the potential for injury to park 

employees and visitors.

• Park staff should maintain a good working relationship 

with state regulators and Ferrell Gas management.

Uranium

Generally speaking, the thin sandstone beds of the 

Chinle Formation contain uranium, in particular the 

Shinarump and Sonsela members; however, the Chinle 

beds exposed in the park contain no specific occurrences 

of uranium (Ron Blakey, Northern Arizona University,

e-mail, October 30, 2008). Furthermore, the potential for 

uranium mining on lands in or near the park is very low 

(National Park Service 2008a). Uranium exploration did 

occur in the Twin Buttes area of the park, as evidenced 

by a number of boreholes, but the nearest uranium mines 

are outside the park, north of Holbrook. These mines 

operated between 1953 and 1960, but were not 

significant contributors to Arizona’s uranium 

production. 

Since 2003, a substantial increase in price and demand 

for nuclear reactor fuel has renewed mining interest in 

some parts of Arizona. However, most deposits in the 

state, including those near Petrified Forest, tend to be of 

lower grade and would have difficulty competing with 

other world sources (National Park Service 2008a).

Perhaps the main concern for resource management 

regarding uranium is protection of groundwater quality.

Groundwater is the park’s primary water resource and, 

until 1997, was the park’s drinking water supply. In 1997, 

the park began purchasing potable water from the 

Navajo Tribal Utility Authority, thereby eliminating the 

need for park managers to operate water supply wells. 

However, park managers are still responsible for 

operating and maintaining the pipelines and distribution 

system that transport water from park facilities in the 

Painted Desert and Rainbow Forest areas (Martin 2004).

The National Park Service identified the uranium mine 

tailings that spill into the Puerco River from the United 

Nuclear dam site near Gallup, New Mexico, as a threat to 

park resources (National Park Service 1986). 

Investigation documented increased radiation in the 

Puerco River near Sander, Arizona, 50 km (30 mi) 

upstream from Petrified Forest National Park; however, 

most of the observed radioactivity in the alluvial aquifer 

in the Sander area was from natural sources and not from 

effluent from mining and milling operations (Dixon 

1990). Nevertheless, the U.S. Geological Survey and NPS 

Water Resources Division (WRD) recommend that park 

managers continue annual sampling of the alluvial 

groundwater to determine whether significant water 

quality changes have taken place (Martin 2004).

In 2003, WRD staff completed a water resources scoping 

report for Petrified Forest National Park, which 

described the general geography and hydrologic 

environment of the park (Whealan et al. 2003). Similar to 

earlier findings, this report documented radionuclides in 

the Puerco River and alluvial groundwater as a product 

of both the natural erosion of uranium-bearing rock and 

past mining-related activities upstream of the park. 

Anthropogenic releases of radionuclides upstream of the 

park have not affected groundwater in the alluvium—the 

source of water for the Puerco Well No. 2. 

In 2004, WRD staff prepared another report (Martin 

2004) that focused solely on the park’s hydrogeology and 

described past efforts to develop groundwater resources 

and made recommendations for future development.

Adjacent Development

In the 1990s, park managers began noting external 

threats from the encroachment of development 

(National Park Service 1994). Recent encroachment 

includes a possible casino on Navajo Nation land at the 

Pinte Road exit east of the park headquarters (Bill 

Parker, Petrified Forest National Park, written 

communication, June 2009). 

On December 3, 2004, Petrified Forest National Park 

more than doubled in size, to approximately 88,448 ha 

(218,553 ac). Although the purpose of the expansion was 

to protect natural resources, it could have unforeseen 

consequences, namely population growth. 

Rudzitis and Johansen (1989a, b) found that, on average, 

wilderness counties grew twice as fast as metropolitan 

areas. Better environmental quality, a slower pace of life, 

and low crime rates have become increasingly important 

amenities for people to consider when choosing a 

location in which to live (e.g., Dillman 1979). To test the 

importance of such values, investigators studied counties 

in the United States that contain or are adjacent to 

federally designated wilderness areas (Rudzitis and 

Johansen 1989a, b). Results from more than 11,000 

randomly selected participants in 15 wilderness counties 

in the West showed that employment opportunities were 

important to 27% of those surveyed, while environment 

or physical amenities were important to 42%. The most 

important qualities of wilderness counties to new 

migrants were found to be scenery (83%), outdoor 

recreation (79%), environmental quality (78%), and pace 

of life (75%). Thus, many people seem to be willing to 

give up financial gain in exchange for wilderness 

amenities. 

Everyday markets also show the economic importance 

(value) of quality of life. For example, a home with a view 

commands a higher price than an identical one without a 

view; the value of the view, then, is the difference in price 

between the two houses (Rasker and Glick 1994). Using 

Petrified Forest as a case study, perhaps the example can 

be taken a step further: a house or a piece of land near a 

wilderness area or national park is more valuable than 

one that is not. The superintendent’s annual report for 

fiscal year 2005 seems to bear this out: “Private land sales 

in the expansion area boomed on eBay and elsewhere, 

going from $100 per acre to $2,000 per acre, and, in two 

sections, from 40 acre parcels split down to 1.5 acre 

parcels” (National Park Service 2005b, p. 1). Therefore, 

proximity to wilderness can result in an increase in 

subdivisions, loss of important wildlife habitat, and 

threats to biodiversity. It can also drive up housing 
PEFO Geologic Resources Inventory Report 13

prices, resulting in a shortage of affordable rental units. 

Development adjacent to the park could result in greater 

access to paleontological resources, and as a result of 

construction, increased erosion and exacerbated eolian 

processes (e.g., dust storms). 

Figure 5. Petrified wood. Congress set aside Petrified Forest National Park to protect one of the world’s largest and most colorful 

concentrations of petrified wood. National Park Service photograph by T. Scott Williams.
14 NPS Geologic Resources Division

Figure 6. Bentonite. Expanding bentonite clays are found in mudstone beds of the Chinle Formation throughout the park. This photo is 

from the Jasper Forest area. National Park Service photograph by T. Scott Williams.
PEFO Geologic Resources Inventory Report 15

Figure 7. Slump terraces. Bentonite-rich mudstones absorb water and expand, becoming “plastic.” The surface layers creep downslope 

forming “terraces” like these visible beneath the Kachina Point Overlook. Arizona Geological Survey image by Larry Fellows in Bezy and 

Trevena (2000).

Figure 8. Cliff retreat. At the Newspaper Rock overlook, hard sandstones of the Newspaper Rock Bed overlie softer mudstones. As the 

mudstone erodes away, unsupported slabs of overlying sandstone break along fractures. The cliff “retreats” as these broken slabs 

topple to the slopes below. National Park Service photograph by Jason Kenworthy (NPS Geologic Resources Division). 
16 NPS Geologic Resources Division

Figure 9. Holbrook Basin potash deposit. Petrified Forest National Park overlies a significant portion of the 1,550-km2 (600-mi2

) potash 

deposit near Holbrook, Arizona. As a result of growing global demand for fertilizer and skyrocketing prices, mining companies are 

increasingly interested in this rich deposit under the park. Graphic (fig. 2) from Rauzi (2008b). Used with permission of the Arizona 

Geological Survey.
PEFO Geologic Resources Inventory Report 17

Geologic Features and Processes

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

in Petrified Forest National Park.

Paleontological Resources

The bibliography of the paleontological resources for

Petrified Forest National Park is substantial, containing 

hundreds of references. This section does not purport to 

summarize all of these references, rather to simply 

highlight the wealth of paleontological resources at the 

park. Tweet et al. (2009) summarized the paleontological 

resources at Petrified Forest National Park and compiled 

a bibliography. In addition, the park’s Web site 

(http://www.nps.gov/pefo/naturescience/fossils.htm; 

accessed November 13, 2009) provides species lists and 

general information about the paleontological resources.

While Petrified Forest National Park is best known for its 

petrified trees, the Chinle Formation—the park’s 

primary strata—hosts a diversity of other plant and 

animal fossils and is one of the richest Upper Triassic 

deposits in the world. As expressed in Houk (2005), in 

the Upper Triassic “an astonishing assortment of animals 

inhabited the land and water of this green world, 

including some of the earliest plant- and meat-eating 

dinosaurs, giant amphibians, flying lizards, fish, clams, 

snails, and experiments in the up-and-coming group 

known as mammals” (p. 66). To date, investigators have 

discovered fossils in the Petrified Forest, Sonsela, and 

Blue Mesa members of the Chinle Formation (table 2);

the Owl Rock and Mesa Redondo members are 

fossiliferous elsewhere. In addition, Quaternary deposits 

in the area have yielded proboscidean (e.g., mammoths)

remains, although not within the park (Tweet et al. 2009). 

The fossils preserved at Petrified Forest National Park 

represent entire ecosystems. Hundreds of fossil sites are 

known: 125 sites with plant megafossils, 152 sites with 

fossil invertebrates, 365 sites with fossil vertebrates, and 

10 sites with trace fossils (Bill Parker, Petrified Forest 

National Park, written communication, September 3, 

2009). The Chinle Formation has yielded more than 200 

different fossil plants, including lycopods, horsetails, 

ferns and fernlike foliage (fig. 10), cycads, cycadeoids, 

ginkgoes, cordaites, conifers in the form of silicified 

wood, compressed leaves, stems, cones, amber, pollen, 

and spores. Fossils of Triassic fauna in the park include 

invertebrates such as bivalves, gastropods, and crayfish; 

and vertebrates such as freshwater fish (e.g., sharks, 

coelacanth, and lungfish), amphibians, archosaurs, and 

therapsids. Archosaurs are a specialized group of animals 

that includes birds and crocodiles. In the Upper Triassic,

archosaurs were represented by aetosaurs, phytosaurs, 

rauisuchians, and dinosaurs. Therapsids were large 

reptiles that possessed many mammalian characters, 

including a “cheek” bone, enlarged canine teeth, a pelvis, 

and a specialized attachment of the skull to the spine

(fig. 11). Phytosaurs (fig. 12) and metoposaurs (a type of 

amphibian) dominate the vertebrate remains at the park 

(Parrish 1989). Trace fossils, which show the presence or 

evidence of behavior but not the actual remains of an 

organism, include insect nests, trails left by horseshoe 

crabs, vertebrate tracks, coprolites (fossil dung), and 

channels and tunnels burrowed into fossilized wood. 

The petrified logs that made the park famous are part of 

the Chinle Formation. The Sonsela Member of the

Chinle Formation is the primary source of petrified 

wood, and hosts the Crystal, Jasper, and Rainbow forests 

in the park. The Blue Mesa Member, which contains the 

majority of fossil-leaf localities, also yields abundant 

petrified wood, as does the Petrified Forest Member. 

The petrifaction process was sometimes so exact that the 

resulting fossils show many details of the logs’ original 

surfaces and occasionally internal cell structures. Many 

of the logs are from an extinct tree called Araucarioxylon 

arizonicum. Two others—Woodworthia and Schilderia—

occur in small quantities in the northern part of the park. 

During the petrifaction process, iron and other minerals 

combined with silica (quartz) to create the rainbowcolored wood (fig. 13). In addition, clear quartz, purple 

amethyst, yellow citrine, and smoky quartz grew in 

cracks in the logs that formed as a result of crushing or 

decay. These minerals enhance the “multicolored 

profusion” and “thousands of random facets” of the 

petrified wood at the park (Schullery 2001, p. 372).

Since 1989, investigators have touted Petrified Forest 

National Park as preserving the “dawn of dinosaurs” 

(Lucas and Hunt 1989). In 1984, when Bryan Small 

discovered “Gertie”—Petrified Forest’s most famous 

fossil (Chindesaurus)—the public fascination with 

dinosaurs was rekindled. In 1995, Long and Murry 

formally described Chindesaurus bryansmalli, named in 

honor of its discoverer and the location of the find 

(Chinde Point). The remains of Triassic dinosaurs such 

as Coelophysis together with Chindesaurus bryansmalli—

actually a dinosaur ancestor—has earned Petrified Forest 

National Park the prestige of being a birthplace of the 

world’s most famous fossils and covering the “dawn” of 

their origin.

Chinle Formation and Badlands Topography

Named for the Chinle Valley north of the park (Gregory 

and Stone 1917), the Chinle Formation comprises most 

of the colorful hills, flat-topped mesas, and sculptured 

buttes of the park’s badlands (fig. 14). The overlying 

Bidahochi Formation also provides some color and 

topographic variety to the badlands terrain. Various 

combinations of minerals in beds of clay and sandstone 

provide the “paint” of the Painted Desert and other 

badlands areas (fig. 15). 

The colorful layers in the Chinle Formation represent 

ancient soil horizons (paleosols). The red and blue layers 

generally contain the same amount of iron and 

manganese, so differences in color depend on the 
18 NPS Geologic Resources Division

position of the groundwater as the ancient soils were 

forming. In soils where the water table was high, a lack of 

oxygen in the sediments resulted in a reducing 

environment, giving the iron minerals in the soil a grayish 

or bluish hue. Reddish soils formed where the water 

table was consistently lower, allowing the iron minerals 

to oxidize (rust). A fluctuating water table caused the 

mottled (gleyed) paleosols in bluish beds.

Rapid erosion is a notable characteristic of the badlands 

terrain, and is easily observable because of the lack of 

vegetative cover. Rugged badlands topography results 

from differential erosion—the effect of weathering and 

erosion on alternating layers of fine-grained, relatively 

soft material and coarser grained, more resistant rock. 

Sandstone, conglomerate, and lava resist erosion, 

forming cliffs that result in the development of mesas. 

Some of the more resistant units form cap rocks on the 

buttes and mesas of the landscape (Harris and Tuttle 

1990). The underlying beds of softer material erode 

much more rapidly and tend to produce sloping hillsides. 

When the cap rock is removed, these softer layers often 

form conical mounds (National Park Service 1986). On a 

smaller scale, differential erosion forms hoodoos—tall 

thin columns of soft sedimentary rock topped by a piece 

of harder, less easily eroded rock (fig. 16).

In addition to hoodoos, the multicolored rocks of the 

Chinle Formation comprise many other landforms—

arroyos, washes, and gullies; plateaus; mesas, buttes, 

monuments, and spires; cuestas; and escarpments. 

Arroyo, Wash, and Gully

Depending on geography (physical and human), either 

the term “arroyo,” “wash,” or “gully” becomes the 

vernacular. According to Stokes (1969), the word 

“arroyo” is used in areas with Spanish influence. Arroyos 

are steep-walled, flat-bottomed desert drainages. 

“Wash,” an English word, has the connotation of wave 

action. During the short rainy period, dry washes can be 

suddenly flooded, but they generally become dry again 

within a few hours (Seff 1962). The term “gully” seems to 

apply to something smaller and shallower than an arroyo 

or wash; it also brings to mind many closely spaced 

tributaries. 

Plateau

A plateau is a large, comparatively flat area with much of 

its surface at summit level. Many other landforms can 

exist on plateaus (Ham 2008); deep valleys often dissect 

and high hills often surmount plateaus (Neuendorf et al. 

2005). Plateaus are considerably elevated above the 

adjacent terrain, generally more than 150 m (490 ft) in 

elevation. Plateaus are higher and more extensive than 

mesas (Neuendorf et al. 2005), which also stand 

distinctly above the surrounding country. 

Mesa, Butte, Monument, and Spire

Mesas, buttes, monuments, and spires can be 

geomorphically grouped. They are all isolated 

conspicuous landforms with steep slopes and flat tops 

that stand distinctly above the surrounding landscape. 

Each is created by erosion, as explained by Stokes (1969):

“a mesa...becomes a butte...becomes a spire...and 

disappears” (p. 26). According to Neuendorf et al. 

(2005), however, a spire is not a defined geomorphic 

form, but would likely come under the definition of 

“monument”—an isolated pinnacle, column, or pillar of 

rock resulting from erosion and resembling a 

manufactured monument or obelisk, usually extremely 

regular in form and of grand dimensions. Mesas are 

bounded by abrupt or steeply sloping erosion scarps on 

all sides and capped by layers of resistant, nearly 

horizontal rock (often lava). A mesa is similar to but has a 

more extensive summit than a butte. Like mesas, buttes 

are often capped with a resistant layer of rock and 

bordered by talus. Both represent an erosional remnant 

carved from flat-lying rocks. 

Cuesta

Like mesas and buttes, cuestas are isolated conspicuous 

landforms that stand distinctly above the surrounding 

landscape. They, too, have steep slopes, but only on one 

side. Unlike mesas and buttes, cuestas do not have flatlying summits; they are asymmetric. Confusingly, Agate 

Mesa in the park is actually a cuesta (Bill Park, Petrified 

Forest National Park, written communication, June 

2009). Differential erosion controls the asymmetry of the 

slopes, with one slope long and gently dipping, and the 

opposite “scarp slope” steep or even clifflike.

Escarpment

When the steep slopes of plateaus, mesas, and cuestas are 

continuous, the term “escarpment” applies. An 

escarpment is a long, more or less continuous cliff or 

relatively steep slope facing in one general direction. 

Escarpments break the continuity of the land by 

separating two level or gently sloping surfaces. They are 

produced by erosion or faulting. In some parts of the 

world (e.g., Great Britain), “cuesta” and “escarpment” 

are synonymous, especially as they refer to the face. 

However, in the southwestern United States, the term 

escarpment is best applied to long continuous features, 

while cuestas are generally more longitudinally limited. 

Unconformities

An unconformity is a surface in the rock record that 

represents a time from which no rocks are preserved in 

an area; that is, either no rocks formed or they formed 

but then eroded away. These surfaces depict “missing” 

rock and “missing” time, often a significant portion of 

“lost” geologic history. Because unconformities are often 

widespread across a region, they are useful for 

correlating rocks of various ages for long distances.

The surface between the Bidahochi Formation and 

Chinle Formation in Petrified Forest National Park is an 

unconformity. Conspicuous for its shape and color, this 

unconformity is nearly horizontal and separates the 

black basalt and yellowish-gray sandstone of the 

Bidahochi Formation (above) from the red mudstone of 

the Chinle Formation (below) (fig. 17). This surface

marks a time gap of about 200 million years. The 

underlying mudstone belongs in the Upper Triassic 

(approximately 228.7 to 199.6 million years ago); the 

overlying volcanic and sedimentary rocks belong to the 
PEFO Geologic Resources Inventory Report 19

Miocene and Pliocene epochs (23 to 2.6 million years 

ago). Based on the large interval of missing time, this 

unconformity likely represents sediments that were 

deposited and later removed by erosion (Bezy and 

Trevena 2000). Comparison to other rocks in the region

indicates that more than 305 m (1,000 ft) of strata were

stripped from this surface (Bezy and Trevena 2000). 

Structural Geology and Features

Rocks in the region of Petrified Forest National Park tilt 

to the northeast at an angle of 1° to 2°. Geologists have 

not mapped any significant faults within Petrified Forest 

National Park (Blakey and Raucci 2006), but gently 

warping strata occurs throughout the park. Conspicuous 

examples of this warping are the sharp syncline of the 

Sinking Ship near Blue Mesa and the broad dome that 

elevates the Newspaper Rock area (Blakey and Raucci 

2006). The colorful sandstone and mudstone layers of 

the Chinle Formation, which were originally deposited in 

the horizontal position during the Triassic Period, 

emphasize the up-warped (anticline) and down-warped 

(syncline) features. Other areas of significant structural 

deformation include a broad upwarp in the Devil’s 

Playground area north of I-40, the subtle synclines of the 

Flattops and Rainbow Forest areas, and Blue Mesa sink 

(see Subsidence section under “Geologic Issues”). The 

Pennsylvanian–Permian Holbrook Basin underlies the 

Petrified Forest region, and mobile salts within this basin 

are the likely cause of warping (Akers 1964) (see Potash 

section under “Geologic Issues”). 

Sedimentary Structures

Sedimentary structures are features of sedimentary rocks 

such as bedding, ripples, and mud cracks; they are 

generally best seen in the field and on the outcrop rather 

than in hand specimen. These structures are generated 

by a variety of sedimentary processes, including fluid 

flow, sedimentary gravity flow, soft-sediment 

deformation, and biogenic activity (Boggs 1995). Because 

they reflect environmental conditions that prevailed at or 

very shortly after deposition, they are of special interest 

to geologists as a tool for interpreting ancient 

depositional environments.

The most common sedimentary structure in the rocks at 

Petrified Forest National Park is cross-bedding—the 

layering of sediment at an angle to the horizontal. Seff 

(1962) noted that both trough and planer cross-bedding 

are abundant in the thick sandstone units. In some of the 

finer siltstones, cross-bedding exists at very low angles 

and often extends laterally for 30 m (100 ft) or more (Seff 

1962). All members of the Chinle Formation and nearly 

all major sandstone bodies within these members host 

cross-bedding (Blakey and Raucci 2006). 

Geomorphologists use cross-bedding to determine the 

strength and direction of ancient wind and water 

currents and to estimate minimum water depth or dune 

height. In the case of the cross-bedding at Petrified 

Forest National Park, these sediments were deposited in 

a fluvial environment (Bezy and Trevena 2000). As sand 

grains moved from upstream to downstream in stream 

channels and on sand bars, various sedimentary 

structures formed. Trough cross-beds generally formed 

in the longitudinal bars of braided rivers and in the 

thalweg (deepest point) of meandering rivers. Lateral 

accretion beds are gently dipping planar cross-beds that 

formed on the point bars of meandering rivers, 

perpendicular to flow direction. Ripple cross-lamination 

is a finer, smaller-scale structure that formed under 

gentler flow conditions with finer grained sediments 

such as silt; sediments settled into horizontal layers and 

water later reworked the sediments into undulating 

ripples. Under higher velocity flow conditions, sand can 

also form horizontal bedding and laminations.

Various investigators (e.g., Seff 1962; Heckert and Lucas 

2002; Blakey and Raucci 2006; Woody 2006) have noted 

other sedimentary structures preserved in the rocks at 

Petrified Forest National Park:

• Lenticular (lens-shaped) bedding—lenses in mud and 

rippled cross-laminated sand where the ripples or 

lenses are discontinuous, not only in the vertical but 

also more or less in the horizontal direction (Reineck 

and Wunderlich 1968).

• Cut-and-fill scours and deposits—sedimentary 

structures consisting of a small erosional channel that 

is subsequently filled with sediment.

• Mudstone rip-ups—flat clasts of mud that have been 

“ripped up” by currents from a semi-consolidated 

deposit of mud and transported to a new depositional 

site.

• Mud cracks—cracks in clay, silt, or mud that formed 

via shrinkage during subaerial dehydration.

• Raindrop and hailstone impressions (or prints)—small, 

shallow, craterlike pits surrounded by a slightly raised 

rim. These impressions form in soft, fine sand, silt, or 

clay by the impact of a falling raindrop or hailstone. 

They are rare features preserved on the bedding planes 

of sedimentary rocks or as casts on the underside of 

overlying sandstone beds.

Eolian Features and Processes

The persistence of the wind is an undeniable part of 

Petrified Forest National Park, and the windblown 

landscape of dunes attests to this fact. According to Bezy 

and Trevena (2000), distinctive forms at the park include 

the following types: (1) barchans (crescent-shaped)

dunes with the “horns” pointing downwind; (2)

transverse dunes with steep downwind but gentle 

upwind slopes that form perpendicular to the prevailing 

wind; and (3) longitudinal dunes—long, narrow, 

symmetrical ridges of sand that form parallel to the 

prevailing wind. Dunes may also be a component of

other landforms (Ham 2008).

Smaller-scale eolian features in the park include desert 

pavement and ventifacts. Desert pavement is a residual 

surface of wind-polished, closely packed cobbles, 

pebbles, and fragments of petrified wood left behind 

after winds have swept away the fine material. Desert 

pavement is often cemented with mineral matter such as 

calcium carbonate (Bezy and Trevena 2000), which 

protects the finer material underneath from wind 
20 NPS Geologic Resources Division

erosion and further deflation. A good example of desert 

pavement occurs 0.8 km (0.5 mi) southwest of the Tepees 

parking area (fig. 1). At this location, sparse vegetation, 

abundant sand, and persistently strong winds create 

perfect conditions for shaping ventifacts (Bezy and 

Trevena 2000). Wind erosion (abrasion/sandblasting) 

shapes, wears, cuts, and polishes pebbles and stones into 

ventifacts. 

Investigators have noted three major drainage basins in 

the park as having eolian landforms: Lithodendron 

Wash, Dry Wash, and Jim Camp Wash (Ellwein 1997; see 

fig. 1). Eolian deposits are thin and uncommon in 

Lithodendron Wash, which is principally underlain by 

easily erodible mudstone; however, a thick mantle of 

eolian material covers the surrounding area. Although 

generally characterized by mesas and buttes (see Chinle 

Formation and Badlands Topography section), Dry 

Wash contains wide alluvial valleys with abundant eolian 

deposits. Finally, eolian deposits are common on the 

drainage divides of Jim Camp Wash.

In 1977, participants in an environmental management 

workshop for Petrified Forest National Park surmised 

that most of the dunes in Lithodendron Wash were a 

result of severe overgrazing at the turn of the 20th

century (Shenk 1977). Since that time, however, 

investigations have revealed a long history of eolian 

development starting in the Pleistocene that includes two 

modes of development. First, linear dunes are present 

only on low-relief surface remnants that formed before 

the development of badlands. Well-developed soils 

reflect the continued geomorphic stability of this surface 

since eolian deposition. Second, superimposed on the 

existing badland landscape are small, constructional 

Holocene dunes. Buried soils identified in middleHolocene deposits suggest multiple episodes of 

deposition followed by periods of stability sufficient to 

enable soil development. The Holocene dunes and soil 

stratigraphy likely reflect the impacts of late Quaternary 

climate changes on the rapidly evolving badlands in 

Petrified Forest National Park (Ellwein et al. 1997). 

Vegetation has stabilized most dunes in the area (Ham 

2008).

Investigators primarily used soil development, but also 

stratigraphic relationships and landforms (e.g., fans and 

pediments), to estimate the ages of eolian deposits 

(Ellwein 1997). The older the dunes, the more welldeveloped the soils associated with them. Ellwein et al. 

(1997) interpreted the oldest dunes as middle Pleistocene 

(75,000 to 200,000 years old). “Middle-aged” dunes—

e.g., those in Lithodendron Wash—are middle Holocene 

(2,000 to 8,000 years old); “young” late-Holocene dunes 

(less than 1,000 years old) occur throughout the park. 

Blakey and Raucci (2006) mapped larger-scale (1:24,000) 

Quaternary (Pleistocene and Holocene) eolian dunes 

and sand sheets; they also noted that eolian processes 

have modified many undifferentiated surficial deposits. 

In a 2002 study, visitors frequently responded that the 

wind was what they “liked least” about their experience 

in the park (Lee et al. 2002). Management concerns 

associated with eolian processes are high erosion rates 

and the associated loss of major archaeological and fossil 

resources (National Park Service 1997). In addition, 

Petrified Forest National Park is very close to the 

threshold for eolian activity in the modern climate 

(Ellwein 1997). Shenk (1977) suggested a variety of 

research questions associated with eolian features and 

processes: (1) What physical processes create the dunes? 

(2) Where are the dunes moving? and (3) Is any material 

coming from outside Petrified Forest National Park? In 

addition, Shenk (1977) recommended that investigators 

study the dunes as an ecosystem.

Volcanic Features

During the late Miocene and early Pliocene (23 to 2.6

million years ago), a large basin with ephemeral lakes 

(playas) covered much of northeastern Arizona. 

Volcanoes nearby, and as far away as southwestern 

Nevada, spewed ash and lava into the basin. Many of the 

volcanoes at this time were phreatomagmatic (i.e., 

groundwater and surface water mingled with magma). 

Ascending magma mixed explosively with watersaturated mud and volcaniclastic sediments. Finegrained ash landed in the lakes and was deposited within 

the sediments. Volcanic deposits of this age in the park 

are part of the Bidahochi Formation.

After a few million years of erosion, most of the 

Bidahochi Formation has been removed from Petrified 

Forest National Park, but three small volcanic 

structures—Pintado Point, Pilot Rock, and Black Knoll—

exist within the park. The erosion-resistant lava flows 

such as Pilot Rock protect the softer lakebed deposits 

beneath. These structures are most likely outliers of the 

Hopi Buttes volcanic field to the northwest (fig. 18); 

however, the San Francisco–Mormon Mountain 

volcanic field to the west and the Springerville–White 

Mountains volcanic field to the southeast are also 

contenders. Plymate et al. (2001) reported that argon40/argon-39 dating of a massive flow unit from each of 

these three structures yielded ages of 4.67 ± 0.66 million 

years for the Pintado Point structure, 5.0 ± 1.4 million 

years for the Pilot Rock structure, and 5.0 ± 1.5 million 

years for the Black Knoll structure. Although these ages 

do not preclude these features from being part of the San 

Francisco–Mormon Mountain or Springerville–White 

Mountains volcanic fields, they are most consistent with 

the timing of the major volcanic activity in the Hopi 

Buttes field (Plymate et al. 2001). 

The Hopi Buttes volcanic field, which extends northwest 

from the northern overlooks of the park, is one of the 

largest concentrations of maar landforms in the world, 

covering about 2,500 km2 (965 mi2

) and containing more 

than 300 maar–tuff ring volcanoes (fig. 18) (White 1991). 

Maars are flat-bottom, roughly circular volcanic cones 

that form from phreatomagmatic explosions near the 

surface. The vent from one of these maars is exposed on 

the rim of the Painted Desert across the park road to the 

east of Pintado Point (see fig. 1). Most of the maars and 

associated diatremes at Hopi Buttes formed between 8.5 

and 6 million years ago. Diatremes—subvolcanic roots or 

subsurface pipes—of individual Hopi Buttes volcanoes 

fed the maars and were filled by volcanic material at the 
PEFO Geologic Resources Inventory Report 21

time of the eruption. They are now exposed because of 

lowering of the land surface by erosion. The youngest 

volcanoes are 4.2 million years old.

The volcanoes of the Hopi Buttes volcanic field are also 

notable for being monogenetic. By definition, 

monogenetic volcanic fields have only one short eruptive

event at each volcano, as opposed to several eruptions 

from the same vent over a long period in their history. 

Monogenetic fields occur only where the magma supply 

to the volcano is low or where vents are not close enough 

or large enough to develop plumbing systems for 

continuous feeding of magma (Wood and Kienle 1990). 

Monogenetic volcanic fields can provide snapshots of 

the region beneath the surface and can be useful in 

studying the generation of magma and the composition 

of the mantle because the single eruption would match 

that of the chamber from which it erupted.

Smaller volcanic features at the park include basaltic 

agglomerate—boulder-, cobble-, and pebble-sized 

fragments of basalt, which violently ejected from nearby 

volcanic vents and cemented with similarly ejected finergrained volcanic ash (Bezy and Trevena 2000). Boulders 

of volcanic agglomerate at Petrified Forest National Park 

are as large as 1.2 m (4 ft) in diameter; such large 

fragments suggest that the source (vent) was not far away

(Bezy and Trevena 2000). Additionally, angular 

fragments of agglomerate ejected out of the vent in the 

solid state; ellipsoidal or football-shaped fragments 

started as blobs of molten rock that molded via rotation 

during flight. These ellipsoidal objects are called 

“volcanic bombs.” Their shapes are determined primarily 

by the viscosity of the molten rock (Bezy and Trevena 

2000).

Stream Terraces

Cut into the north flank of the Puerco River valley are 

two large steplike surfaces. These are stream terraces—

erosional remnants of the active floodplain that existed 

during the late Pleistocene to Holocene epochs. The 

terraces stand hundreds of feet about the Puerco River, 

but dip in the same general direction as the floodplain. 

During at least two episodes of erosion, the Puerco River 

cut down its channel and by shifting from one side of the 

valley to the over, removed all but these vestiges of the 

former valley floors (Bezy and Trevena 2000). 

Stream terraces at lower levels can be subject to flooding 

during unusual weather events. The terraces are 

composed of stratified sandy, gravelly, loamy, silty, or 

clayey sediments and, in some cases, by buried paleosols. 

The parent material is alluvium (Ham 2008).

Tinajas

Natural potholes, called “tinajas,” are a significant source 

of surface water in the arid Southwest. Tinajas form over 

time through fluvial processes that scour out the massive, 

homogeneous, non-fractured bedrock. They appear to 

form along mathematically predictable spacing, although 

no formal studies that look at distribution have been 

conducted (GRI scoping notes, Organ Pipe Cactus 

National Monument, January 25, 2006). Tinajas 

primarily occur in areas where bedrock is exposed at the 

surface, such as the Upper Triassic sandstone of the 

Chinle Formation. 

Past investigators mistakenly identified tinajas in the park 

as reptile nests, but recent studies have clarified the 

features as “inorganic weathering pits” lacking evidence 

for positive identification as a tetrapod nest (Lucas and 

Hunt 2006).

Desert Varnish

Also called “rock varnish,” desert varnish coats many 

rocks in Petrified Forest National Park. Varnish forms on 

all types of surfaces, from flat-lying desert pavement (see 

Eolian Features and Processes section) to mesa walls, but 

it seems to form best on harder rocks with high silica 

content (Stokes 1969). The often lustrous staining ranges 

in color from light brown to black, depending on how 

much has accumulated. Varnishes are complex 

combinations of clays and birnessite (manganese oxide) 

or iron oxides such as magnetite, maghemite, and 

hematite (Probst et al. 2001). Varnished rocks in the 

Southwest have special archaeological significance 

because of the prehistoric petroglyphs pecked through 

the mineral skin to the fresh rock below (fig. 19) (Bezy 

and Trevena 2000). Geomorphologists use desert varnish 

as a relative age indicator of the geomorphic surfaces 

upon which the varnish developed (Quade 2001). 

Because varnish forms at variable rates, however, it 

cannot be used reliably to date the human inscriptions

(Bezy and Trevena 2000). 

Rock varnish also provides evidence for deciphering past 

climate in the western United States. According to Liu 

and Broecker (2008), rock varnish provided evidence of 

nine millennial-scale wet events between 18,000 and 

11,500 calendar years before present. Preliminary 

radiometric age calibration indicates that these events are 

broadly coeval with millennial-scale cooling events 

identified in the ice core record of the Greenland Ice 

Sheet Project 2 (Liu and Broecker 2008). These results, 

combined with previous documentation of millennialscale wet events in the Holocene varnish record for the 

same region, indicate that such wet oscillations in the 

western United States may be part of regionally 

widespread manifestation of the North Atlantic climate 

(Liu and Broecker 2008).

Scientists and observers of nature have long debated two 

questions about desert varnish: (1) Is it microbially 

mediated? and (2) What is its genesis? Perry et al. (2003) 

addressed the first question by analyzing scrapings of 

desert varnish from the Sonoran Desert in Arizona and 

the Mojave Desert in California. These investigators 

found 13 amino acids, indicating a biogenic component 

of these varnishes, which may play a role in their 

formation. As for the second question, many observers 

have suggested that varnish is splashed or dripped onto 

rocks during storms and, as the water evaporates, the 

mineral matter stays behind, gradually forming a smooth 

coat. Now that manganese-oxidizing microorganisms 

have been implicated in the formation of desert varnish, 

the evaporation theory is outdated. Furthermore, 
22 NPS Geologic Resources Division

scientists (e.g., Flood et al. 2001) have confirmed that the 

most likely elemental source for desert varnish is 

windblown dust.

Finally, desert varnish may preserve yet another 

paleontological resource in Petrified Forest National 

Park. Probst et al. (2001) investigated whether desert 

varnish can preserve a fossil record of the organisms that 

created the coatings. Scientists examined manganeseand iron-rich varnishes on granitic substrates from the 

Sonoran Desert in Arizona. The varnishes appear as 

toroidal-shaped and honeycomb-textured chains and 

cells—“biofabrics”—composed of clay minerals, in 

which single and colonial microorganisms in various 

stages of decay and fossilization are embedded. The 

study concluded that these features are suitable media 

for the preservation of microfossils (Probst et al. 2001). 

Furthermore, Krinsley (1998) determined that small 

coccoid and granular structures within the varnish 

matrix have a much higher concentration of iron and 

manganese than the surrounding matrix, and may in fact 

be bacterial casts, hyphae, buds, or bacterial precipitates.

Caliche

Petrified Forest National Park is located on the border of 

Navajo and Apache counties, Arizona. A typical soil 

profile in these counties contains as much as 36%

calcium carbonate (Ham 2008). Silt and dust from the 

atmosphere are an important source of this carbonate. 

Under semi-arid conditions, soils with such notable 

amounts of calcium carbonate often form layers of 

caliche—a general term for concentrations of soluble 

calcium salts (e.g., calcium carbonate) that precipitate 

from soil moisture at or near the ground surface. Caliche 

occurs at Petrified Forest National Park because rainfall 

is insufficient to flush calcium salts from the soil. Some 

buried caliche zones may have formed during past 

periods of greater rainfall or increased accumulation of 

carbonate from the atmosphere (Bezy and Trevana 

2000).

Ham (2008) noted calcium carbonate pendants and thick 

coatings on gravel in the soils in the area. Additionally 

calcium carbonate sometimes forms a “hardpan” layer, 

nodules, or tubes. A hardpan is an impervious layer of 

soil lying at or just below the surface. It is a result of 

cementation of soil particles, in this case with calcium 

carbonate. Nodules form when calcium carbonate 

precipitates from downward percolation of water, or less 

commonly, from moisture brought up from below by 

evaporation and capillary rise. Tubes occur when 

calcium carbonate coats and eventually replaces plant 

roots (Bezy and Trevena 2000).

Table 3. Types of fossils in the Chinle Formation at Petrified Forest National Park

Figure 10. Fern fossil. While the petrified logs are the most well known plant fossils from the park, many other taxonomic groups and plant 

structures are represented. The fern Phlebopteris smithii is shown here. National Park Service photograph.

Member Petrified 

Wood

Leaves and 

Other Plant 

Remains

Fungi Invertebrate 

Remains

Invertebrate 

Trace Fossils

Vertebrate 

Remains

Vertebrate 

Trace Fossils

Petrified 

Forest X X X X X X

Sonsela X X X X X X

Blue Mesa X X X X X X X
PEFO Geologic Resources Inventory Report 23

Figure 11. Placerias skeleton. Placerias was a large therapsid, colloquially known as a “mammal-like reptile.” Therapsid fossils are not common 

within Petrified Forest National Park, but are well known from other parts of Arizona. National Park Service photograph. 

Figure 12. Phytosaur skull. Phytosaurs are distantly related to crocodiles (note the elongated snout) and are the most common fossil animal 

found within Petrified Forest National Park. National Park Service photograph. 
24 NPS Geologic Resources Division

Figure 13. Rainbow-colored petrified wood. Most of the petrified wood in the park is from Araucarioxylon arizonicum, an extinct tree of 

Triassic age. Two others types of wood, Woodworthia and Schilderia, occur in small quantities in the northern part of the park. Iron and other 

minerals combined with silica created the rainbow colors. All types of quartz crystals—clear quartz, purple amethyst, yellow citrine, and 

smoky quartz—add to the colorful display. National Park Service photograph by T. Scott Williams.

Figure 14. Badlands topography. The colorful hills, flat-topped mesas, and sculptured buttes of the park’s badlands (this photo is from the 

Blue Mesa area) are composed of the Upper Triassic Chinle Formation, named for the Chinle Valley north of the park. The horizontal colored 

bands represent paleosols (ancient soil layers). National Park Service photograph by Marge Post.
PEFO Geologic Resources Inventory Report 25

Figure 15. Painted Desert. Colorful badlands of the Chinle Formation comprise the Painted Desert in Petrified Forest National Park. National 

Park Service photograph by T. Scott Williams.

Figure 16. Erosion. Eagle Nest Rock was a prominent 5 m (15 ft) pillar (hoodoo) in the Jasper Forest bed of the Sonsela Member, and a popular 

attraction for early visitors to the park. Shaped by erosion, the feature also succumbed to erosive forces following a period of high rainfall 

and high winds in January 1941. National Park Service photographs by George Grant (1934) and T. Scott Williams (2007).
26 NPS Geologic Resources Division

Figure 17. Unconformity. The arrow points to the contact between the yellow-gray sandstones and black basalts of the Miocene-aged 

Bidahochi formation (above) and the red mudstones of the Triassic-aged Chinle Formation (below). This unconformity represents about 200 

million years of missing time. Arizona Geological Survey photograph by Larry Fellows in Bezy and Trevena (2000). 

Figure 18. Hopi Buttes volcanic field. Within Petrified Forest National Park, rocks of the Bidahochi Formation are most likely outliers from the 

large Hopi Buttes volcanic field. This volcanic field is one of the world’s largest concentrations of maar landforms (note the dark-colored 

cones in the image above). The volcanic field is approximately 80 km (50 mi) across. Aerial imagery compiled by Phil Reiker (NPS Geologic 

Resources Division) from ESRI ArcImage Service; USA Prime Imagery.
PEFO Geologic Resources Inventory Report 27

Figure 19. Petroglyphs. Prehistoric peoples etched petroglyphs into desert varnish throughout the Southwest. Petrified Forest National Park 

contains many examples. National Park Service photograph by T. Scott Williams. 
28 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 Petrified Forest National Park. 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 Petrified Forest 

National park provided information for the “Geologic 

Issues,” “Geologic Features and Processes,” and 

“Geologic History” sections of this report. Geologic 

maps are two-dimensional representations of complex 

three-dimensional relationships; their color coding 

illustrates the distribution of rocks and unconsolidated 

deposits. Bold lines that cross or separate the color 

patterns mark structures such as faults and folds. Point 

symbols indicate features such as dipping strata, sample 

localities, mines, wells, and cave openings. 

Incorporation of geologic data into a Geographic 

Information System (GIS) increases the usefulness of 

geologic maps by revealing the spatial relationships 

among geologic features, other natural resources, and 

anthropogenic features. Geologic maps are indicators of 

water resources because they show which rock units are 

potential aquifers and are useful for finding seeps and 

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

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

factor in soil formation. Furthermore, resource managers 

have used geologic maps to make connections between 

geology and biology; for instance, geologic maps have 

served as tools for locating sensitive, threatened, and 

endangered plant species, which may prefer a particular 

rock unit. 

Although geologic maps do not show where earthquakes 

will occur, the presence of a fault indicates past 

movement and possible future seismic activity. Similarly, 

map units show areas that have been susceptible to 

hazards such as landslides, rockfalls, and volcanic 

eruptions. Geologic maps do not show archaeological or 

cultural resources, but past peoples may have inhabited 

or been influenced by depicted geomorphic features. For 

example, alluvial terraces may have been preferred use 

areas and formerly inhabited alcoves may occur at the 

contact between two rock units.

The geologic units listed in the following table 

correspond to the accompanying digital geologic data. 

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

Please refer to the geologic timescale (fig. 20) for the age 

associated with each time period. The table highlights 

characteristics of map units such as: susceptibility to 

erosion and hazards; the occurrence of paleontological 

resources (fossils), cultural resources, mineral resources, 

and caves or karst; and suitability as habitat or for 

recreational use. Some information on the table is 

conjectural and meant to serve as suggestions for further 

investigation.

The GRI digital geologic maps reproduce essential 

elements of the source maps including the unit 

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

The following references are the sources for the GRI 

digital geologic data for Petrified Forest National Park, 

which covers the pre-2004 boundary: 

Blakey, R., and Raucci, J. 2006. Geologic map of Petrified 

Forest National Park, Arizona. Scale 1:24,000. 

Unpublished data. Flagstaff, AZ: Northern Arizona 

University. 

This publication incorporated new mapping and the 

following sources:

Billingsley, G. H. 1985a. Geologic map of Petrified Forest 

National Park, Arizona. Scale 1:48,000. Unpublished 

data. Petrified Forest, AZ: Petrified Forest Museum 

Association.

Johns, M. E. 1988. Architectural element analysis and 

depositional history of the upper Petrified Forest 

Member of the Chinle Formation, Petrified Forest 

National Park, Arizona. MS thesis, Northern Arizona 

University.

Woody, D. 2003. Revised geological assessment of the 

Sonsela Member, Chinle Formation, Petrified Forest 

National Park, Arizona. MS thesis, Northern Arizona 

University.

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, and increases the overall 

utility of the data. GRI digital geologic map products 

include data in ESRI personal geodatabase, shapefile, 

and coverage GIS formats, layer files with feature 

symbology, Federal Geographic Data Committee 

(FGDC)-compliant metadata, a Windows help file that

contains all of the ancillary map information and 

graphics, and an ESRI ArcMap map document file that 

easily displays the map.

GRI digital geologic data are included on the attached 

CD and are available through the NPS Natural Resource 

Information Portal at 

http://science.nature.nps.gov/nrdata/
PEFO Geologic Resources Inventory Report 29

Map Unit Properties Table: Petrified Forest National Park

Age Map Unit

(Symbol) Description Exposure and Thickness Paleontological, Mineral, and Cultural Resources

Suitability for 

Infrastructure and 

Recreation

Correlation

QUATERNARY

Surficial deposits, 

undifferentiated

(Qsu)

Unconsolidated sand, silt, mud, and gravel: Includes alluvial surfaces (slopewash and 

sheet-flow deposits), active stream channels (ephemeral and perennial), colluvium, 

floodplain deposits, in situ soil development, and deposits of indeterminate origin; may 

be superficially modified by eolian processes

Alluvium is up to 60 m (200 ft) thick (Martin 

2004)

Alluvium produces 

sufficient water, but 

would require treatment 

(Martin 2004); colluviumcovered slopes indicate 

potential for mass 

movement

Eolian dunes and sand sheets 

(Qd)

Unconsolidated sand: Deposited in dunes by eolian processes or in extensive sand sheets 

by mixed alluvial and eolian processes; commonly heavily vegetated

200,000- to 75,000-year-old dunes at higher 

elevations in north part of the park; 8,000- to 

2,000-year-old dunes in drainages (e.g., 

Lithodendron Wash); <1,000-year-old dunes 

throughout the park (Ellwein et al. 1997)

MIOCENE/

PLIOCENE

Bidahochi Formation

Volcanic rocks

(Mbv) Basaltic lava and tephra deposits: Likely part of the Hopi Buttes volcanic field Restricted to north portion of park (e.g., Headquarters Mesa)

Landmark features (e.g., Pilot 

Rock and Black Knoll)

Equivalent to the informal 

Member 5 of the Bidahochi 

Formation (Dallege 1999)

MIOCENE

Sedimentary rocks 

(Mbs)

Mudstone and minor siltstone: Deposited in freshwater lake or basin with shallow 

ephemeral lakes; outcrops generally medium tan to yellow, and locally difficult to 

distinguish from overlying Quaternary deposits; present as cut-and-fill deposits atop the 

Petrified Forest Member (TRcpf); usually preserved by volcanic cap rock

Limited outcrops near and south of 

Headquarters Mesa, on Pilot Rock, and in the 

northeast corner of the park

Likely equivalent to Members 

1 and 2 of Dallege (1999)

unconformity

TRIASSIC

Chinle Formation

Owl Rock Member 

(TRco)

Sandstone and mudstone with minor limestone and siltstone: Lacustrine; mudstones—

generally lighter in color than the underlying Petrified Forest Member (TRcpf); 

sandstones—pale reddish brown, fine-grained, well-sorted litharenites with common 

trough cross-strata; limestones—generally light-colored, mottled, pisolithic, and massive, 

locally brecciated and re-cemented; approximately 205 million years old (Bill Parker, 

Petrified Forest National Park, written communication, June 2009)

Exposed only on Chinde Mesa in the far north 

part of park, where 80 m (260 ft) are present 

(Ash 1992)

Limestone with secondary 

silica in dissolution zones 

(Dubiel 1993; Tanner 2000);

selenite-gypsum lenses and 

chalcedony nodules; caliche

Bentonite; dissolution 

zones

Petrified Forest 

Member1

(TRcpf)

Mudstone with minor sandstone and siltstone: Deposited in vast, muddy floodplain; 

primarily pale red to purple mudstone with common thin sandstone interbeds; 

commonly bright reddish orange north of I-40; commonly light-green mottling in 

mudstones and large-scale scours in the upper part of the unit; approximately 210 

million years old (Bill Parker, Petrified Forest National Park, written communication, 

June 2009)

Approximately 255 m (840 ft) thick (Ash 1992); 

exposed in Flattops and Painted Desert areas

Petrified wood; fossil leaves 

and other plant remains; 

invertebrate and vertebrate 

remains and trace fossils; 

gypsum

Bentonite

Called the Painted Desert 

Member (Petrified Forest 

Formation, Chinle Group) by 

Heckert and Lucas (2002)

Black Forest Bed 

(TRcpfbf)

Calcrete-nodule conglomerate and reworked tuffaceous material with sandstone and 

mudstone interbeds: Black silicified wood gives bed its name; dated isotopically at 213 ± 

1.7 million years old (Riggs et al. 2003) and 211 ± 0.7 million years old (Heckert et al. 

2009)

Conglomerate up to 13 m (4 ft); sandstone and 

mudstone (0.1 to 0.2 m [0.3 to 0.7 ft] thick); 

only exposed in north part of park

Known for permineralized 

black wood; invertebrate and 

vertebrate remains

Lithodendron 

Wash Bed 

(TRcpflw)

Sandstone, conglomerate, and mudstone: Generally fine-grained sandstone with minor 

conglomerate, coarse-grained sandstone and interbedded mudstone; sandstones pale 

gray to tan on fresh surfaces, but commonly weather to medium brown; internal crossstratification is ubiquitous, including trough and planar cross-sets, lateral accretion sets, 

and rare channel forms; multi-storied or single sets

Present throughout south part of the Petrified 

Forest Wilderness; total thickness up to 11 m 

(36 ft); many mesas and buttes of Painted 

Desert developed in this bed (Heckert and 

Lucas 2002)

Bentonite

Called Painted Desert 

Sandstone 3 by Billingsley 

(1985a) and Johns (1988)

Goblin Sandstone 

(TRcpfg)

Sandstone and minor conglomerate: Pale yellowish gray to pale red, fine-grained, wellsorted; planar and trough cross-bedding are common, as are small-scale scours and ripup conglomerates at the base of coarse-grained bedsPresent west of Chinde Point (forms the floor 

of washes); prominent ledge-former in the 

Devil’s Playground area

May be equivalent to Painted 

Desert Sandstone 1 of 

Billingsley (1985a) and Johns 

(1988)

Flattops Beds 2–4 

(TRcpff)

Sandstone: Generally fine- to medium-grained, moderately to well-sorted brownish gray 

sandstone; commonly planar and trough cross-strata are common and horizontal and 

ripple laminae

Flattops Bed 2 laterally extensive; Flattops 

Beds 3 and 4 restricted to the Flattops Mesa 

area along the main park road; unit thicknesses 

laterally variable but typically <10 m (33 ft);

Flattops Bed 2 is the thickest (>10 m [33 ft] in 

some locations)

Unionid bivalves in Flattops 

Beds 2 and 3
PEFO Geologic Resources Inventory Report 30

1

Since mapping by Blakey and Raucci (2006), Martz and Parker (2010) have reinterpreted the Petrified Forest Member as (from oldest to youngest) Flattops Bed 2, Flattops Bed 3, and Flattops Bed 4. 2

Mapped by Blakey and Raucci (2006) as an informal unit only in the Devil’s Playground area north of I-40. 3

Since mapping by Blakey and Raucci (2006), Martz and Parker (2010) revised the Sonsela Member into the following beds (from oldest to youngest): Camp Butte beds, Lot’s Wife beds, Jasper Forest bed / Rainbow Forest Bed, Jim Camp beds, and Martha’s Butte beds. 4

Lower sandstone unit mapped by Blakey and Raucci (2006) is probably within the lower part of the Blue Mesa Member (Bill Parker, Petrified Forest National Park, written communication, September 3, 2009).

Age Map Unit

(Symbol) Description Exposure and Thickness Paleontological, Mineral, and Cultural Resources

Suitability for 

Infrastructure and 

Recreation

Correlation

TRIASSIC

Chinle Formation

Sonsela Member / 

Petrified Forest 

Member 

undifferentiated 

(TRcspf)

Mudstone and sandstone: Pale greenish gray to bluish gray mudstone with minor to 

significant sandstone interbeds; commonly tabular bedding and cut-and-fill scours; 

lateral variation in lithology, becoming generally finer grained to the north

Informal unit mapped only in the Devil’s 

Playground area north of I-40 (Blakey and 

Raucci 2006)

Bentonite

Transitional interval between 

the Sonsela and Petrified 

Forest members (Blakey and 

Raucci 2006)

Sonsela Member3

Deposited in large gravelly river; entirely within Norian Stage (216.5 to 203.6 million 

years ago), approximately 216 million years ago (Bill Parker, Petrified Forest National 

Park, written communication, June 2009)

Includes the majority of strata in the central 

and southern portion of the park as well as the 

Devils Playground area

Primary source of petrified 

wood in the park; other plant, 

invertebrate, and vertebrate 

remains and trace fossils

Flattops 1 Bed 

(TRcsft1)

Sandstone and conglomerate: Medium- to coarse-grained, moderately to well-sorted, 

yellow brown to dark brown sandstone; compositionally immature and commonly 

multi-storied with thin mudstone interbeds; conglomerates comprise calcrete-nodule 

lags at the base of sandstone beds and discrete lenses of pebble-size clasts; volcanic clasts 

and intra-formational rip-ups

Individual beds 3 to 5 m (10 to 16 ft) thick; 

maximum thickness 25 m (80 ft), but appears 

to pinch out in the southeast and west edges of 

the south part of the park

Petrified wood and unionid 

bivalves; chert

Top of the Sonsela Member 

in Woody (2003); called 

Agate Bridge Bed by Heckert 

and Lucas (2002)

Brown Sandstone 

(TRcsb)

Sandstone and minor conglomerate: Sandstones generally fine- to medium-grained, but 

coarse intervals common, especially near the base of scours; pale tan or gray on fresh 

surfaces, weathers to medium brown; internal structure—massive or weakly laminated to 

complex cross-stratification; may comprise either multiple stories or a single thick bed; 

forms prominent blocky ledges

Mapped only in the Devil’s Playground area 

north of I-40 (Blakey and Raucci 2006); total 

unit thickness up to 6 m (20 ft), but lateral

changes in thickness can be abrupt, especially 

near the northern pinch-out

Jasper Forest Bed 

(TRcsjf) Sandstone, mudstone, and conglomerate Caps bluffs at Blue Mesa, Jasper Forest, and Crystal Forest

Main petrified wood-bearing 

horizon in the central portion 

of the park; vertebrate 

remains occur locally

Called the Agate Bridge Bed 

by Heckert and Lucas (2002); 

may be analogous to one or 

more significant, medial 

sandstones within the Jim 

Camp Wash Beds in the 

Rainbow Forest area

Jim Camp Wash 

Beds

(TRcsjc)

Sandstone, siltstone, and mudstone: Pale gray, purple, and less commonly red mudstone; 

fine- to medium-grained and poorly sorted sandstone; sandstones—generally not 

laterally continuous, ribbon architecture common; thicker, more laterally continuous 

sandstone beds are locally present that are coarser grained, richer in volcanic clasts, and 

similar to Rainbow or Flattops sandstones from which they may be difficult to 

distinguish

Total thickness 30 to 45 m (100 to 150 ft), may 

locally thinner

Unionid bivalve fragments; 

vertebrate fossils; minor 

amounts of petrified wood; 

chert and calcareous nodules

Bentonite

Rainbow Forest 

Beds

(TRcsrf)

Sandstone and conglomerate: Fine- to medium-grained, moderately well-sorted, pale 

gray sandstone; locally trough and planar cross-stratified

Individual beds are generally 1 to 4 m (3 to 13 

ft) thick; total thickness up to 15 m (50 ft)

Main wood-bearing horizon 

in southern end of park, 

contains nearly all the more 

colorful specimens; andesite, 

rhyolite, chert, and quartzite 

in conglomerate

Basal bed of the Sonsela 

Member; tentatively includes 

the Camp Butte sandstone 

(Murry 1990)

Blue Mesa Member 

(TRcbm)

Mudstone with minor siltstone and sandstone: Deposited in muddy floodplain, ancient 

soils; banded dark blue, gray, yellow, and red; structureless beds; base is approximately 

219 million years old (Irmis and Mundi 2008)

Individual beds generally >2 m (7 ft) thick;

total thickness 80 m (260 ft); base rarely 

exposed in park, best exposed in the Tepees 

area

Contains majority of fossilleaf localities, as well as 

abundant petrified wood, 

including stumps in growth 

position, amber, pollen, and 

spores; vertebrate remains

common in some horizons

Bentonite

Newspaper Rock 

Bed

(TRcbmn)

Sandstone, shales, mudstone, and conglomerate: Deposited in meandering fluvial 

system; complex internal geometry, including trough cross-strata, stacked ripple 

laminations, and lenticular bedding

Up to 20 m (66 ft) thick, and includes 

prominent red paleosol horizon in the Tepees 

and Blue Mesa areas; lowest persistent ledgeforming sandstone in the park

Contains majority of fossilleaf localities; fossil plants 

and fungi; vertebrate tracks

Sandstone facies prone to 

cliff retreat

Prominent bed in the Blue 

Mesa Member

Lower sandstone unit4

(TRcls)

Sandstone: Coarse-grained quartoze with significant quartz overgrowths; irregular and 

lenticular bedding and trough cross-strata

Exposed in a single isolated outcrop east of the 

Haystacks; total thickness up to 2 m (7 ft); 

individual beds 0.5 to 1 m (2 to 3 ft) thick, 

cross-bedding in 20- to 40-cm (8- to 16-in) sets

Mesa Redondo

Member

(TRclrm)

Pale-red mudstone: Deposited in a combination of fluvial environments; >219 million 

years ago (Bill Parker, Petrified Forest National Park, written communication, June 2009)

Uncertain thickness; only the top of the unit is 

exposed in the park
PEFO Geologic Resources Inventory Report 31

Geologic History

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

geologic map of Petrified Forest National Park, the environment in which those units

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

During the Upper Triassic Period, about 220 million 

years ago, Petrified Forest National Park was located just 

north of the equator on the southwestern edge of the 

supercontinent Pangaea, which spread from pole to pole. 

Much of Earth’s surface was covered by a large ocean 

called Panthalassa. Pangaea was shaped like a huge letter 

“C” facing eastward (fig. 21). The open part of the “C” 

cupped the Tethys Ocean. The spine of the “C” ran 

adjacent to a long subduction zone, which formed the 

eastern margin of the ocean basin. Pangaea began to 

break apart during the Triassic Period, but dispersed 

mostly during the Jurassic. Just as the formation of 

Pangaea influenced geologic and biologic events during 

the Paleozoic Era, the breakup of this supercontinent 

profoundly affected geologic and biologic events during 

the Mesozoic Era. The movement of continents affected 

ocean circulation and climatic regimes. Populations 

became isolated and were brought into contact with 

other populations, leading to evolutionary changes in the 

biota.

Ancient soils and fossil plants and animals indicate that 

the climate was humid and subtropical during Upper 

Triassic time. However, the rocks of Petrified Forest 

National Park show evidence of an increasingly arid 

climate and a transition from low-sinuosity perennial 

streams to mostly ephemeral streams and small lakes in 

younger rocks (Johns 1988; Tanner 2000; Woody 2003).

The regional setting of Petrified Forest National Park 

was a single depositional basin or closely interconnected 

array of sub-basins (Stewart et al. 1972a, b; Lucas 1993). 

The Chinle Formation is a sequence of nonmarine strata 

of Upper Triassic age that was deposited into this vast 

basin, which extended north-south from Wyoming to 

Texas, and east-west from western Oklahoma to 

southeastern Nevada—an area of about 2.3 million km2

(0.9 million mi2

) (Lucas 1992).

Triassic (refer to fig. 20 for a geologic timescale) 

volcanism resulted in the deposition of ash in the park, 

which weathered to form bentonitic clay. Investigators 

have identified the volcanic source material as coming 

from far and near. Dubiel (1994) suggested that a 

magmatic-volcanic arc on part of the western edge of 

Pangaea likely provided volcanic ash, as well as clastic 

detritus to the Chinle deposition basin. Harris (1977) 

extrapolated that the volcanic ash may have been 

transported by the wind from volcanic fields in Nevada. 

Some have suggested more local source areas—the 

Mogollon Highlands to the south of the park and the 

Uncompahgre Highlands to the north (Smiley 1985). 

These areas also provided clastic sediments (Dubiel 

1994). The deposited ash, whatever its source(s), leached 

the silica responsible for the petrifaction of the park’s 

famous logs (National Park Service 2003).

The sedimentary layers of the Chinle Formation—the 

principal fossil-bearing strata in the park—consist of 

sandstone, siltstone, mudstone, conglomerate (i.e., silica 

and limestone pebbles and calcrete nodules), and minor 

limestone beds (in the Owl Rock Member). These rocks 

preserve a suite of lowland terrestrial environments, 

including river channels, floodplains, swamps, and small 

lakes (Dubiel 1994; Blakey and Raucci 2006). Each 

member details the stratigraphy, sedimentology, and 

paleontology of a particular depositional setting.

Mesa Redondo Member

The Mesa Redondo Member records a combination of 

fluvial environments: fast through-flowing streams 

carried considerable runoff (represented by highly crossbedded conglomerate) and slowly moving streams in 

broad floodplains deposited fine-grained sediments 

(represented by mudstone and siltstone) (Cooley 1958). 

The Mesa Redondo Member is not well exposed in the 

park, but limited outcrops of rocks underlying the Blue 

Mesa Member are present near the Haystacks in the 

southern part of the park (fig. 1).

Blue Mesa Member

The lowest (oldest) well-defined rock unit in Petrified 

Forest National Park is the Blue Mesa Member of the 

Chinle Formation. Approximately 219 million years ago, 

streams deposited the strata of the Blue Mesa Member, 

which are best exposed at the Tepees area in the 

southern part of the park (Lucas 1993; Heckert and 

Lucas 1995b; Irmis and Mundil 2008). These rocks 

represent part of a vast muddy tropical floodplain 

(Dubiel 1989; Demko 1995a, b). Plants growing at this 

time included conifer trees, cycadeoids, cycads, and 

ferns (Ash 2005). Small rivers meandered across the 

landscape, heading northwestward toward the 

Panthalassa shoreline located near the Utah-Nevada 

border. Large plant eaters such as the cow-sized 

mammal-like reptile Placerias browsed along the river 

banks (Lucas 2001).

Sonsela Member

About 216 million years ago, large gravelly rivers 

deposited the Sonsela Member of the Chinle Formation 

in a wide fluvial plain (Dubiel 1989). These rivers carried 

heavier bedloads than either earlier or later Triassic river 

channels preserved at Petrified Forest National Park 

(Blakey and Gubitosa 1984). The change from a muddy 

floodplain of the Blue Mesa Member likely resulted from 

a slowing of the rate at which the crust was subsiding in 

western North America at this time (Blakey and Gubitosa 
32 NPS Geologic Resources Division

1984). Large conifer trees grew along the rivers, and their 

fossilized stumps and logs became the park’s renowned 

petrified forests (Heckert and Lucas 1995a). Plant-eating 

reptiles, such as the heavily armored Paratypothorax, 

foraged on the forest floors (Lucas 2001).

Petrified Forest Member

About 210 million years ago, when the red-bed 

mudstones and sandstones in the Painted Desert formed, 

the Triassic river system was once again a vast muddy 

floodplain (Blakey and Gubitosa 1984; Dubiel 1989). 

Unlike the floodplain of the older Blue Mesa Member, 

however, huge rivers meandered across the PetrifiedForest-Member floodplain, and tall trees lined the 

watercourses. These trees became the logs of the Black 

Forest near Kachina Point. Crocodile-like phytosaurs, 

some as long as 7 m (23 ft), hunted along the river banks 

(Lucas 2001).

Owl Rock Member

Sediments settled in a lake and formed the Owl Rock 

Member 205 million years ago. This member represents 

the southern extension of a lacustrine system that was 

centered on the Four Corners area of the Colorado 

Plateau (see fig. 4). Gastropods at the base of the Owl 

Rock Member attest to the original lacustrine setting for 

some of the beds, though many of the strata were 

subsequently altered by pedogenesis (soil formation) 

while exposed under drier conditions and lowered lake 

levels (Dubiel 1993; Tanner 2000). Lucas (1992) referred 

to these deposits as “soil caliches” (see Caliche section 

under “Geologic Features and Processes”). The lateral 

extent of the Owl Rock Member’s limestone beds (some 

of which are laminated), as well as invertebrate burrows 

and gastropods in the intervening siltstones, add 

credence to a lacustrine interpretation for the Owl Rock 

Member (Dubiel 1993).

Jurassic and Cretaceous Rocks

Since deposition of the Triassic rocks, tectonic forces 

have uplifted northeastern Arizona by at least one 

vertical mile. Working in concert, uplift and erosion 

removed any Jurassic and Cretaceous (between 200 and 

65.5 million years ago) rocks that may have been present.

Miocene-Pliocene and Quaternary Units

Although the Upper Triassic Chinle Formation 

dominates the geologic setting of Petrified Forest 

National Park, rocks and unconsolidated deposits from 

two other geologic time intervals are part of the park’s 

landscape: Miocene–Pliocene Bidahochi Formation and 

Quaternary deposits.

Bidahochi Formation

Sedimentary and volcanic rocks of the Bidahochi 

Formation cap higher mesas in the Painted Desert area. 

Bidahochi sediments settled in a freshwater-lake 

environment and became mudstone and siltstone. This 

lake—called Lake Bidahochi by Smiley (1985) and Lake 

Hopi by Dallegge (1999) and Blakey and Raucci (2006)—

was regionally extensive and persisted until late Miocene 

or early Pliocene time. The section at Petrified Forest 

National Park represents only the early phases of 

deposition in the Bidahochi basin (Dallegge 1999). 

Alternatively, the Bidahochi setting may have been a 

basin that contained many ephemeral lakes (Dallegge et 

al. 2000). Vents of the Hopi Buttes volcanic field erupted 

lava and ash into the lake of the lower Bidahochi 

Formation, creating a series of maar deposits and lava

flows. Basaltic rocks also formed landmark features such 

as Pilot Rock and Black Knolls in the park. The 

Bidahochi Formation spans about 5 million years from 

approximately 9 to 4 million years ago (Love 1989). 

Erosion has removed much of the Bidahochi Formation 

from the park area. 

Quaternary Deposits

Sediments of the Quaternary Period (the past 2. 6 million 

years) consist of fluvial (river-deposited) mud, silt, sand, 

and gravel, and eolian (wind-deposited) sand that form 

extensive dunes and sand sheets. These sediments cover 

the Miocene-Pliocene and Triassic rocks throughout 

much of the park. 

Presently, synchronous forces of deposition and erosion 

are creating new sedimentary layers and landforms such 

as sand dunes and stream channels while stripping away 

older rocks and exposing fossil flora and fauna.
PEFO Geologic Resources Inventory Report 33

Figure 20. Geologic timescale. Included are major life history and tectonic events occurring on the North American continent. Red lines 

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

the regional location of individual geologic events. Adapted by Trista Thornberry-Ehrlich (Colorado State University) from the U.S. Geological 

Survey, http://pubs.usgs.gov/fs/2007/3015/ with additional information from the International Commission on Stratigraphy 

http://www.stratigraphy.org/view.php?id=25.
34 NPS Geologic Resources Division

Figure 21. Pangaea. During the Upper Triassic Period, Petrified Forest National Park was located just north of the equator on the western 

edge of the supercontinent Pangaea. The west coast of Pangaea was situated along a subduction zone; the eastern shoreline cups the Tethys 

Ocean. At the time, much of Earth’s surface was covered by a large ocean called Panthalassa. Base paleogeographic images by Ron Blakey 

(Northern Arizona University Department of Geology); available at http://jan.ucc.nau.edu/~rcb7/index.html (accessed May 2010).
PEFO Geologic Resources Inventory Report 35

Glossary

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

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

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

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

alluvium. Stream-deposited sediment.

anticline. A convex-upward (“A” shaped) fold. Older 

rocks are found in the center.

aquifer. A rock or sedimentary unit that is sufficiently 

porous that it has a capacity to hold water, sufficiently 

permeable to allow water to move through it, and 

currently saturated to some level.

arroyo. A small, deep, flat-floored channel or gully of an 

ephemeral or intermittent stream in the arid and 

semiarid regions of the southwestern United States.

ash (volcanic). Fine pyroclastic material ejected from a 

volcano (also see “tuff”).

barchan dune. A crescent-shaped dune with arms or 

horns of the crescent pointing downwind. The 

crescent or barchan type is most characteristic of 

inland desert regions.

basin (structural). A doubly plunging syncline in which 

rocks dip inward from all sides.

basin (sedimentary). Any depression, from continental to 

local scales, into which sediments are deposited.

bed. The smallest sedimentary strata unit, commonly 

ranging in thickness from one centimeter to a meter or 

two and distinguishable from beds above and below.

bedding. Depositional layering or stratification of 

sediments.

bedrock. A general term for the rock that underlies soil 

or other unconsolidated, surficial material.

calcareous. Describes rock or sediment that contains the 

mineral calcium carbonate (CaCO3).

cementation. Chemical precipitation of material into 

pores between grains that bind the grains into rock.

chalcedony. A variety of quartz that is commonly fibrous

on a microscopic level, may be translucent or 

semitransparent, and has a nearly wax-like luster.

chemical sediment. A sediment precipitated directly from 

solution (also called nonclastic).

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.

clast. An individual grain or rock fragment in a 

sedimentary rock, produced by the physical 

disintegration of a larger rock mass.

clastic. Describes rock or sediment made of fragments of 

pre-existing rocks (clasts).

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

sedimentary fragment size classification (less than 

1/256 mm [0.00015 in]).

claystone. Lithified clay having the texture and 

composition of shale but lacking shale’s fine layering 

and fissility (characteristic splitting into thin layers).

conglomerate. A coarse-grained, generally unsorted, 

sedimentary rock consisting of cemented, rounded 

clasts larger than 2 mm (0.08 in).

cross-bedding. Uniform to highly varied sets of inclined 

sedimentary beds deposited by wind or water that 

indicate flow conditions such as water flow direction 

and depth.

cuesta. An asymmetric landform with one gently sloping 

side and one steeply sloping side. Results from erosion 

of gently dipping rock strata.

deformation. A general term for the process of faulting, 

folding, and shearing of rocks as a result of various 

Earth forces such as compression (pushing together) 

and extension (pulling apart).

dip. The angle between a bed or other geologic surface 

and horizontal.

dome. General term for any smoothly rounded landform 

or rock mass. More specifically refers to an elliptical 

uplift in which rocks dip gently away in all directions.

drainage basin. The total area from which a stream 

system receives or drains precipitation runoff.

dune. A low mound or ridge of sediment, usually sand, 

deposited by wind. Common dune types include 

“barchan,” “longitudinal,” “parabolic,” and

“transverse” (see respective listings).

eolian. Describes materials formed, eroded, or deposited 

by or related to the action of the wind. Also spelled 

“Aeolian.”

ephemeral stream. A stream that flows briefly only in 

direct response to precipitation in the immediate 

locality and whose channel is at all times above the 

water table.

escarpment. A steep cliff or topographic step resulting 

from vertical displacement on a fault or by mass 

movement. Also called a “scarp.”

fault. A break in rock along which relative movement has 

occurred between the two sides.

formation. Fundamental rock-stratigraphic unit that is 

mappable, lithologically distinct from adjoining strata, 

and has definable upper and lower contacts.

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

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

geology. The study of Earth including its origin, history, 

physical processes, components, and morphology.

gully. A small channel produced by running water in 

earth or unconsolidated material (e.g., soil or a bare 

slope).

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.

isotopic age. An age expressed in years and calculated 

from the quantitative determination of radioactive 
36 NPS Geologic Resources Division

elements and their decay products; “absolute age” and 

“radiometric age” are often used in place of isotopic 

age but are less precise terms.

lamination. Very thin, parallel layers.

landslide. Any process or landform resulting from rapid, 

gravity-driven mass movement.

lava. Still-molten or solidified magma that has been 

extruded onto Earth’s surface though a volcano or 

fissure.

litharenite. Short for “lithic arenite.” Describes

sandstone containing >25% fine-grained rock 

fragments; <10% feldspar; and <75% quartz, quartzite, 

and chert.

longitudinal dune. Dune elongated parallel to the 

direction of wind flow.

maar. A low-relief, broad volcanic crater formed by 

multiple shallow explosive eruptions; it may contain a 

lake.

member. A lithostratigraphic unit with definable 

contacts; a member subdivides a formation.

mesa. A broad, flat-topped erosional hill or mountain 

bounded by steeply sloping sides or cliffs.

mineral. A naturally occurring, inorganic crystalline solid 

with a definite chemical composition or compositional 

range.

monument. An isolated pinnacle, column, or pillar of 

rock resulting from erosion and resembling an 

anthropogenic monument or obelisk.

mud cracks. Cracks formed in clay, silt, or mud by 

shrinkage during dehydration at Earth’s surface.

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

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

overburden. Rock and sediment, not of economic value, 

and often unconsolidated, that overlies an ore, fuel, or 

sedimentary deposit.

paleogeography. The study, description, and 

reconstruction of the physical landscape from past 

geologic periods.

Pangaea. A theoretical, single supercontinent that 

existed during the Permian and Triassic periods.

parabolic dune. Crescent-shaped dune with horns or 

arms that point upwind.

parent rock. Rock from which soil, sediments, or other 

rocks are derived.

pediment. A gently sloping, erosional bedrock surface at 

the foot of mountains or plateau escarpments.

pisolite. A sedimentary rock, commonly limestone, made 

up chiefly of rounded, pea-sized grains called pisoliths.

plastic. Capable of being deformed permanently without 

rupture.

plateau. A broad, flat-topped topographic high (both 

terrestrial and marine) of great extent and elevation 

above the surrounding plains, canyons, or valleys.

point bar. A low ridge of sand and gravel deposited in a 

stream channel on the inside of a meander where flow 

velocity slows.

radioactivity. The spontaneous decay or breakdown of 

unstable atomic nuclei.

red bed. Sedimentary strata composed largely of 

sandstone, siltstone, and shale that are predominantly 

red due to the presence of ferric iron oxide (hematite)

coating individual grains.

ripple marks. The undulating, approximately parallel and 

usually small-scale ridge pattern formed on sediment 

by the flow of wind or water.

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

sabkha. A coastal environment in an arid climate just 

above high tide. Characterized by evaporate minerals, 

tidal-flood, and eolian deposits. Common in the 

Persian Gulf.

sand. A clastic particle smaller than a granule and larger 

than a silt grain, having a diameter in the range of 1/16 

mm (0.0025 in) to 2 mm (0.08 in).

sandstone. Clastic sedimentary rock of predominantly 

sand-sized grains.

scarp. A steep cliff or topographic step resulting from 

displacement on a fault, or by mass movement, or 

erosion. Also called an “escarpment.”

sediment. An eroded and deposited, unconsolidated 

accumulation of rock and mineral fragments.

sedimentary rock. A consolidated and lithified rock 

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

of the three main classes of rocks—igneous, 

metamorphic, and sedimentary.

sequence. A major informal rock-stratigraphic unit that 

is traceable over large areas and defined by a sediments 

associated with a major sea level transgressionregression.

shale. A clastic sedimentary rock made of clay-sized 

particles that exhibit parallel splitting properties.

silt. Clastic sedimentary material intermediate in size 

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

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

siltstone. A variably lithified sedimentary rock composed 

of silt-sized grains.

slope. The inclined surface of any geomorphic feature or 

measurement thereof. Synonymous with “gradient.”

slump. A generally large, coherent mass movement with a 

concave-up failure surface and subsequent backward 

rotation relative to the slope.

soil. Surface accumulation of weathered rock and 

organic matter capable of supporting plant growth and 

often overlying the parent material from which it 

formed.

spring. A site where water issues from the surface due to 

the intersection of the water table with the ground 

surface.

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.

stream. Any body of water moving under gravity flow in 

a clearly confined channel.

subsidence. The gradual sinking or depression of part of 

Earth’s surface.

syncline. A downward curving (concave up) fold with 

layers that dip inward; the core of the syncline 

contains the stratigraphically-younger rocks.

system (stratigraphy). The group of rocks formed during 

a period of geologic time.

tectonic. Relating to large-scale movement and 

deformation of Earth’s crust.
PEFO Geologic Resources Inventory Report 37

tectonics. The geologic study of the broad structural 

architecture and deformational processes of the 

lithosphere and aesthenosphere.

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

transverse dune. Dune elongated perpendicular to the 

prevailing wind direction. The leeward slope stands at 

or near the angle of repose of sand whereas the 

windward slope is comparatively gentle.

tuff. Generally fine-grained, igneous rock formed of 

consolidated volcanic ash.

type locality. The geographic location where a 

stratigraphic unit (or fossil) is well displayed, formally 

defined, and derives its name. The place of original 

description.

unconformity. An erosional or non-depositional surface 

bounded on one or both sides by sedimentary strata. 

An unconformity marks a period of missing time.

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

movement that raises the rocks.

vent. An opening at Earth’s surface where volcanic 

materials emerge.

volcanic. Describes anything related to volcanoes. Can 

refer to igneous rock crystallized at or near Earth’s 

surface (e.g., lava).

wash. A term used especially in the southwestern United 

States for the broad, gravelly dry bed of an intermittent 

stream, generally in the bottom of a canyon; it is 

occasionally swept by a torrent of water.

water table. The upper surface of the saturated zone; the 

zone of rock in an aquifer saturated with water.

weathering. The physical, chemical, and biological 

processes by which rock is broken down.

PEFO Geologic Resources Inventory Report 39

Literature Cited

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

available from the National Park Service Geologic Resources Division.

Akers, J. P. 1964. Geology and ground water in the central 

part of Apache County, Arizona. Water-supply paper 

1771. Reston, VA: U.S. Geological Survey.

Ash, S. R. 1992. The Black Forest Bed: A distinctive unit 

in the Upper Triassic Chinle Formation, northeastern 

Arizona. Journal of the Arizona-Nevada Academy of 

Science 24/25:59–73.

Ash, S. R. 2005. Synopsis of the Upper Triassic flora of 

Petrified Forest National Park and vicinity. In 

Guidebook to the Triassic Formations of the Colorado 

Plateau in Northern Arizona: Geology, Paleontology, 

and History, ed. S. J. Nesbitt, W. G. Parker, and R. B. 

Irmis, 59–70. Bulletin 6. Mesa, AZ: Mesa Southwest 

Museum.

Attarian, A. 2003. Swatting litter bugs: What agencies can 

do to decrease depreciative visitor behavior. Parks & 

Recreation (November 1, 2003).

http://www.thefreelibrary.com/_/print/PrintArticle.as

px?id=111403395 (accessed November 13, 2009).

Bezy, J. V. and A. S. Trevena. 2000. Guide to geologic 

features at Petrified Forest National Park. Down-toEarth 10. Tucson, AR: Arizona Geological Survey.

Billingsley, G. H. 1985a. General stratigraphy of the 

Petrified Forest National Park, Arizona. In The 

Petrified Forest through the Ages, ed. E. H. Colbert and 

R. R. Johnson, 3–8. Bulletin 54. Flagstaff, AZ: Museum 

of Northern Arizona.

Billingsley, G. H. 1985a. Geologic map of Petrified Forest 

National Park, Arizona. Scale 1:48,000. Unpublished 

data. Petrified Forest, AZ: Petrified Forest Museum 

Association.

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PEFO Geologic Resources Inventory Report 45

Additional References

This section lists additional references, resources, and web sites that may be of use to 

resource managers. Web addresses are current as of June 2010.

General Geology and Paleontology

Paleobiology Database: http://paleodb.org/cgibin/bridge.pl

Ron Blakey (Northern Arizona University) 

paleogeographic reconstructions: 

http://jan.ucc.nau.edu/~rcb7/index.html

Geology of National Park Service Areas

National Park Service Geologic Resources Division 

(Lakewood, Colorado). http://nature.nps.gov/geology/

NPS Geologic Resources Inventory. 

http://www.nature.nps.gov/geology/inventory/index.c

fm

U.S. Geological Survey Geology of National Parks 

(includes 3D photographs). 

http://3dparks.wr.usgs.gov/

Harris, A. G., E. Tuttle, and S. D. Tuttle. 2003. Geology of 

National Parks. Sixth Edition. Kendall/Hunt 

Publishing Co., Dubuque, Iowa, USA.

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

parklands. John Wiley and Sons, Inc., New York, New 

York, USA.

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

national parks, monuments, and seashores. W.W. 

Norton and Co., New York, New York, USA.

[Geared for interpreters].

NPS Geoscientist-in-the-parks (GIP) internship and 

guest scientist program. 

http://www.nature.nps.gov/geology/gip/index.cfm

Resource Management/Legislation Documents

NPS 2006 Management Policies (Chapter 4; Natural 

Resource Management): 

http://www.nps.gov/policy/mp/policies.html#_Toc157

232681

NPS-75: Natural Resource Inventory and Monitoring 

Guideline: 

http://www.nature.nps.gov/nps75/nps75.pdf.

NPS Natural Resource Management Reference Manual 

#77: http://www.nature.nps.gov/Rm77/

Geologic Monitoring Manual

R. Young and L. Norby, editors. Geological 

Monitoring. Geological Society of America, Boulder, 

Colorado.

[Website under development]. Contact the Geologic 

Resources Division to obtain a copy.

NPS Technical Information Center (Denver, repository 

for technical (TIC) documents): http://etic.nps.gov/

Geological Survey Websites

Arizona Geological Survey: http://www.azgs.state.az.us/

U.S. Geological Survey: http://www.usgs.gov/

Geological Society of America: 

http://www.geosociety.org/

American Geological Institute: http://www.agiweb.org/

Association of American State Geologists: 

http://www.stategeologists.org/

Other Geology/Resource Management Tools

Bates, R. L. and J. A. Jackson, editors. American 

Geological Institute dictionary of geological terms (3rd 

Edition). Bantam Doubleday Dell Publishing Group, 

New York.

U.S. Geological Survey National Geologic Map Database 

(NGMDB): http://ngmdb.usgs.gov/

U.S. Geological Survey Geologic Names Lexicon 

(GEOLEX; geologic unit nomenclature and summary): 

http://ngmdb.usgs.gov/Geolex/geolex_home.html

U.S. Geological Survey Geographic Names Information 

System (GNIS; search for place names and geographic 

features, and plot them on topographic maps or aerial 

photos): http://gnis.usgs.gov/

U.S. Geological Survey GeoPDFs (download searchable 

PDFs of any topographic map in the United States): 

http://store.usgs.gov (click on “Map Locator”).

U.S. Geological Survey Publications Warehouse (many 

USGS publications are available online): 

http://pubs.usgs.gov

U.S. Geological Survey, description of physiographic 

provinces: http://tapestry.usgs.gov/Default.html
46 NPS Geologic Resources Division

Appendix A: Overview of Digital Geologic Data

The following pages are an overview of the digital geologic data for Petrified Forest 

National Park. For poster-size PDFs of these overviews and complete digital data, please 

see the included CD or visit the Geologic Resources Inventory publications web site:

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

Note: Digital geologic data was produced prior to the park’s expansion in 2004.


PEFO Geologic Resources Inventory Report 49

Appendix B: Scoping Session Participants

The following is a list of participants from the GRI scoping session for Petrified Forest 

National Park, held on June 27–28, 2001. The contact information and email addresses 

in this appendix may be outdated; please contact the Geologic Resources Division for 

current information. The scoping meeting summary was used as the foundation for this 

GRI report. The original scoping summary document is available on the GRI web site: 

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

Name Affiliation Phone E-Mail

Sid Ash NPS, PEFO 505-856-5852 sidash@aol.com

Karen Beppler NPS, PEFO 928-624-6228, ext. 263 karen_beppler@nps.gov

George Billingsley USGS 928-556-7198 gbillingsley@usgs.gov

James Charles NPS, NAVA superintendent 928-672-2700 james_charles@nps.gov

Sue Clements NPS, PEFO tecumseh@selway.umt.edu

Tim Connors NPS, GRD 303-969-2093 tim_connors@nps.gov

Helen Fairley NPS, Flagstaff area 928-526-1157 helen_fairley@nps.gov

Tracey Felger NPS, GRCA GIS 520-556-7164 tracey_felger@nps.gov

John Graham Colorado State University 970-225-6333 jpgraham250@msn.com

Scott Graham USGS 928-556-7270 sgraham@usgs.gov

Sarah Hanson NPS, SUCR GIP 520-526-0502; 517-264-3944 slhanson@adrian.edu

Ron Hiebert NPS, NAU-CESU 520-523-0877 ron.hiebert@nau.edu

Todd Metzger NPS, Flagstaff todd_metzger@nps.gov

Michael Ort Northern Arizona University 928-523-9363 michael.ort@nau.edu

Bill Parker PEFO paleontologist william_parker@nps.gov

Dave Sharrow NPS, PISP 435-644-4318 dave_sharrow@nps.gov

Nicole Tancreto NPS, Flagstaff 928-556-7466, ext. 240 nicole_tancreto@nps.gov

Paul Whitefield NPS, Flagstaff area parks 928-526-1157 paul_whitefield@nps.gov

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 110/104279, June 2010 
National Park Service 

U.S. Department of the Interior 

Natural Resource Program Center 

1201 Oakridge Drive, Suite 150 

Fort Collins, CO 80525 

www.nature.nps.gov 

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