Walnut Canyon National Monument 

Geologic Resource Evaluation Report 

Natural Resource Report NPS/NRPC/GRD/NRR—2008/040 

National Park Service 

U.S. Department of the Interior 

Natural Resource Program Center 
THIS PAGE: THIS PAGE: 

Walnut Canyon, Walnut Canyon NM Walnut Canyon, Walnut Canyon NM 

 NPS Photo by Sid Covington

ON THE COVER: ON THE COVER: 

View across Walnut Cany View across Walnut Canyon from the Island Trail on from the Island Trail

 USGS photo by Phil Stoffer USGS photo by Phil Stoffer 
Walnut Canyon National Monument 

Geologic Resource Evaluation Report 

Natural Resource Report NPS/NRPC/GRD/NRR—2008/040 

Geologic Resources Division 

Natural Resource Program Center 

P.O. Box 25287 

Denver, Colorado 80225 

June 2008 

U.S. Department of the Interior 

Washington, D.C.
The Natural Resource Publication series addresses natural resource topics that are of interest 

and applicability to a broad readership in the National Park Service and to others in the 

management of natural resources, including the scientific community, the public, and the NPS 

conservation and environmental constituencies. Manuscripts are peer- reviewed to ensure that 

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

intended audience, and is designed and published in a professional manner. 

Natural Resource Reports are the designated medium for disseminating 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. Examples of the diverse array of reports published in this 

series include vital signs monitoring plans; "how to" resource management papers; 

proceedings of resource management workshops or conferences; annual reports of resource 

programs or divisions of the Natural Resource Program Center; resource action plans; fact 

sheets; and regularly- published newsletters. 

Views and conclusions in this report are those of the authors and do not necessarily reflect 

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not constitute endorsement or recommendation for use by the National Park Service. 

Printed copies of reports in these series may be produced in a limited quantity and they are 

only available as long as the supply lasts. This report is also available from the Geologic 

Resource Evaluation Program website (http://www2.nature.nps.gov/geology/inventory/

gre_publications) on the internet, or by sending a request to the address on the back cover. 

Please cite this publication as: 

Graham, J. 2008. Walnut Canyon National Monument Geologic Resource Evaluation Report. 

Natural Resource Report NPS/NRPC/GRD/NRR—2008/040. National Park Service, Denver, 

Colorado. 

NPS D- 38, June 2008 
 WACA Geologic Resource Evaluation Report iii 

Table of Contents 

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

List of Tables ................................................................................................................ iv

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

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

Purpose of the Geologic Resources Evaluation Program...........................................................................................2

Location and Regional Setting....................................................................................................................................2

Regional Geology.......................................................................................................................................................2

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

Geologic Issues........................................................................................................... 10

Rockfall.....................................................................................................................................................................10

Geomorphology and Hydrogeology..........................................................................................................................10

Secondary Geologic Issues......................................................................................................................................12

Geologic Features and Processes............................................................................. 16

Geomorphic Features...............................................................................................................................................16

Sedimentary Features ..............................................................................................................................................16

Tectonic Deformation ...............................................................................................................................................17

Fossils ......................................................................................................................................................................17

Map Unit Properties .................................................................................................... 22

Map Unit Properties Table........................................................................................................................................23

Geologic History.......................................................................................................... 24

Permian Period.........................................................................................................................................................24

Triassic Period..........................................................................................................................................................25

The Missing Record..................................................................................................................................................25

Miocene to Recent....................................................................................................................................................26

Glossary....................................................................................................................... 32

References................................................................................................................... 34

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

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

Attachment 1: Geologic Resource Evaluation Products CD 
iv NPS Geologic Resources Division 

List of Figures 

Figure 1. Regional location map for Walnut Canyon National Monument. .....................................................................5

Figure 2 Trails and relief in Walnut Canyon National Monument. ..................................................................................6

Figure 3. Shaded relief map...........................................................................................................................................7

Figure 4. Cliff dwellings at Walnut Canyon.....................................................................................................................8

Figure 5. Generalized stratigraphic column....................................................................................................................9

Figure 6. San Francisco Volcanic Field........................................................................................................................14

Figure 7. Sample of the fossiliferous limestone in the Kaibab Formation.....................................................................15

Figure 8. Photo of Walnut Canyon ...............................................................................................................................19

Figure 9. Cross-bedded Coconino Sandstone. ............................................................................................................20

Figure 10. Schematic of converging and diverging lithospheric plates.........................................................................21

Figure 11. Geologic time scale.....................................................................................................................................27

Figure 12. Generalized paleogeographic map. ............................................................................................................28

Figure 13. Paleogeographic map of northern Arizona..................................................................................................29

Figure 14. Paleogeographic map of the Early Triassic.................................................................................................30

Figure 15A. Late Cretaceous interior seaway ..............................................................................................................31

Figure 15B. Map of streams in the Walnut Canon........................................................................................................31

List of Tables 

Table 1. Invertebrate fossils from the Kaibab Formation in Walnut Canyon NM area..................................................18
 WACA Geologic Resource Evaluation Report 1 

Executive Summary 

This report accompanies the digital geologic map for Walnut Canyon National Monument 

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

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

Walnut Canyon National Monument was established in 

1915 to protect and preserve the cliff dwellings of the 

Sinagua culture. The Sinagua occupied the region from 

about 1100 to 1220 A.D., and constructed their dwellings 

in alcoves eroded into relatively soft sandstone layers 

beneath harder, resistant limestone ledges. The cliff 

dwellings are in the upper third of Walnut Canyon, 

which Walnut Creek has incised into relatively 

horizontal layers of Paleozoic limestone and sandstone. 

The primary geologic issue facing Walnut Canyon 

resource management is rockfall. Rockfall is a natural 

process that has shaped Walnut Canyon for thousands of 

years. However, rockfall can have a significant impact on 

visitor and staff safety, park infrastructure, and 

archaeological resources in the park. There is a specific 

hazard within the canyon along the Island Trail where 

climate related factors contribute to the timing of 

rockfall events. In addition, large, angular blocks of 

limestone from the Kaibab Formation have narrowed the 

canyon floor in places. 

Another important geologic resource management issue 

is the combined geomorphic and hydrogeologic 

response to decreased water flow in Walnut Creek. 

Decreased sediment input reduced streambed scouring 

and recharge from alluvial aquifers. In the monument, 

approximately 80 acres of riparian vegetation grows on 

the floor of Walnut Canyon. Loss of this native 

vegetation because of decreased flows would not only 

eliminate the riparian landscape, indicative of the natural 

setting at the time of the Sinagua, but also negatively 

impact the viewshed from primary visitor use areas. 

Two dam impoundments upstream of Walnut Creek 

have altered the character of the stream, the riparian 

ecosystem, and the limited water resources within the 

monument. The impoundment and diversion of Walnut 

Creek since 1941 have negatively affected wetland, 

floodplain, and riparian habitats that depend on a 

scoured channel, periodic flooding, and available 

groundwater. To help assess the sustainability of the 

riparian corridor within Walnut Canyon, field studies 

and baseline documentation are needed to identify and 

monitor geomorphic changes and groundwater flow. 

Other geologic issues include volcanic eruptions, 

seismicity, mass wasting, flash flooding, potential aquifer 

contamination, and fossil theft. Approximately 1,000 

years ago, volcanic eruptions produced the Sunset Crater 

in the San Francisco volcanic field north of Walnut 

Canyon. Future eruptions that would produce volcanic 

ash and cinders are possible, but not predictable with 

current technology. Earthquakes along local normal 

faults pose only a minor threat to the infrastructure and 

archaeological resources at the park. However, the 

Anderson Mesa fault and the smaller Marshall Lake 

fault, both located south of the monument, show 

evidence of recent movement. 

Although stream flow has decreased in Walnut Creek, 

flash flooding remains a potential hazard. Intense 

thunderstorms may produce flash floods from local 

tributary canyons. Flooding in Walnut Canyon would 

also occur if either of the two upstream dams were to 

catastrophically fail. 

Fossils are present in the limestone ledges of the Kaibab 

Formation outcrop along park trails making them 

vulnerable to theft. The majority of the paleontological 

resources at Walnut Canyon are marine invertebrates. 

Spiral impressions of snails, molds of small clams, and 

brachiopods are the most common fossils along the 

trails. 

The porous Coconino Sandstone is an important 

regional aquifer in northern Arizona and provides the 

only reliable groundwater beneath the monument at a 

depth of approximately 460 m (1,500 ft). The National 

Park Service maintains a well into the aquifer, and the 

water table has remained relatively stable. Under current 

conditions, there is little threat of contamination or 

aquifer depletion within the watershed. However, the 

city of Flagstaff has annexed all lands to the north and 

west of the monument boundary and any development 

there could significantly increase non- point source 

pollution in perched aquifers, springs, and seeps that 

flow into the canyon. 
2 NPS Geologic Resources Division 

Introduction 

The following section briefly describes the National Park Service Geologic Resource 

Evaluation Program and the regional geologic setting of Walnut Canyon National 

Monument. 

Purpose of the Geologic Resources Evaluation Program 

The Geologic Resource Evaluation (GRE) Program is 

one of 12 inventories funded under the NPS Natural 

Resource Challenge designed to enhance baseline 

information available to park managers. The program 

carries out the geologic component of the inventory 

effort from the development of digital geologic maps to 

providing park staff with a geologic report tailored to a 

park’s specific geologic resource issues. The Geologic 

Resources Division of the Natural Resource Program 

Center administers this program. The GRE team relies 

heavily on partnerships with the U.S. Geological Survey, 

Colorado State University, state surveys, and others in 

developing GRE products. 

The goal of the GRE Program is to increase 

understanding of the geologic processes at work in parks 

and provide sound geologic information for use in park 

decision making. Sound park stewardship relies on 

understanding natural resources and their role in the 

ecosystem. Geology is the foundation of park 

ecosystems. The compilation and use of natural resource 

information by park managers is called for in section 204 

of the National Parks Omnibus Management Act of 1998 

and in NPS- 75, Natural Resources Inventory and 

Monitoring Guideline. 

To realize this goal, the GRE team is systematically 

working towards providing each of the identified 270 

natural area parks with a geologic scoping meeting, a 

digital geologic map, and a geologic report. These 

products support the stewardship of park resources and 

are designed for non- geoscientists. During scoping 

meetings the GRE team brings together park staff and 

geologic experts to review available geologic maps and 

discuss specific geologic issues, features, and processes. 

The GRE mapping team converts the geologic maps 

identified for park use at the scoping meeting into digital 

geologic data in accordance with their innovative 

Geographic Information Systems (GIS) Data Model. 

These digital data sets bring an exciting interactive 

dimension to traditional paper maps by providing 

geologic data for use in park GIS and facilitating the 

incorporation of geologic considerations into a wide 

range of resource management applications. The newest 

maps come complete with interactive help files. As a 

companion to the digital geologic maps, the GRE team 

prepares a park- specific geologic report that aids in use 

of the maps and provides park managers with an 

overview of park geology and geologic resource 

management issues. 

For additional information regarding the content of this 

report and up to date GRE contact information please 

refer to the Geologic Resource Evaluation Web site 

(http://www2.nature.nps.gov/geology/inventory/). 

Location and Regional Setting 

Walnut Canyon National Monument is located 

approximately 11 km (7 mi) east of Flagstaff, Arizona. The 

monument was established in 1915 to protect the areas 

natural resources and ancient Native American ruins that 

date from about 1100 to 1220 A.D. Access to the 

monument is by a paved road to the northern rim of 

Walnut Canyon from Interstate- 40 and by various 

unpaved roads from the adjacent Coconino National 

Forest, managed by the U.S. Forest Service (fig. 1). The 

park road ends at a visitor center on the northern rim of 

the canyon. Island and Rim trails are the only two hiking 

trails managed and maintained by Walnut Canyon 

National Monument (fig. 2). Public use is limited to these 

designated trails and adjacent picnic areas (NPS 2003; 

Hansen et al. 2004). 

The monument covers 3,579.46 acres and ranges in 

elevation from 1,890 to 2,100 m (6,200 to 6,900 ft). The 

stream and canyon are named after the Arizona walnut 

trees that grow along the floor of the canyon (Vandiver 

1936; NPS 2003). 

A moderately hot and moist summer, cool and dry spring 

and fall, and cold, periodically wet, winter typify the 

semi- arid, continental climate of Walnut Canyon 

National Monument (Hansen et al. 2004). Average 

annual precipitation at the monument headquarters is 

approximately 51 centimeters (cm) (20 in) (Thomas 

2003). Monsoon- like precipitation events occur 

principally from July through September, often in the 

form of intense thunderstorms of short duration. 

Regional Geology 

Walnut Canyon National Monument is part of the 

Colorado Plateau Physiographic Province consisting of 

high plateaus, deep narrow canyons, and broad, rounded 

uplands covering an area of 83,200,ooo acres in northern 

Arizona, northwestern New Mexico, western Colorado, 

and southeastern Utah. To the south, the Colorado 

Plateau ends abruptly along the Mogollon Rim, a roughly 

320 km (200 mile) long, faulted escarpment that cuts 

across much of central Arizona. 

The main geologic and topographic feature of Walnut 

Canyon National Monument is Walnut Canyon, an 

entrenched segment of Walnut Creek. The canyon 

trends from west to east and is incised into the Coconino 
 WACA Geologic Resource Evaluation Report 3 

Plateau that extends from the South Rim of the Grand 

Canyon to Flagstaff. Walnut Canyon averages 402 m 

(1,320 ft) wide from the north rim to the south rim, 122 m 

(400 ft) deep at the western (upstream) boundary, and 76 

m (250 ft) deep at the eastern (downstream) boundary. 

Anderson Mesa rises above the Coconino Plateau south 

of Walnut Canyon (fig. 3). Cherry Canyon is a major 

drainage to the southeast of Walnut Canyon. 

The resistant gray limestone of the Permian Kaibab 

Formation caps the upper walls of Walnut Canyon (fig. 

5). This same formation forms the rims of Grand Canyon 

and the higher, relatively flat mesas surrounding the 

narrow canyon within the monument. Locally, more 

than 111 m (364 ft) of massive, resistant limestone and 

dolomite of the Kaibab interbedded with thin, less 

resistant siltstones and sandstones form characteristic 

ledges and slopes. The ancient dwellings in Walnut 

Canyon were constructed under the shelter of 

overhanging ledges of Kaibab limestone 61 m (200 ft) or 

more above the canyon bottom (fig. 4). 

The light- tan Permian Coconino Sandstone underlies 

the Kaibab Formation (fig. 5). The Coconino Sandstone 

is a distinctive cross- bedded sandstone unit that formed 

when the regression of an ancient sea exposed vast tracts 

of sand to prevailing winds , blowing the sand into large 

dune fields similar to the modern Sahara. In this area of 

the Colorado Plateau, the massive cross- bedded 

sandstones of the Coconino are difficult to differentiate 

from cross- bedded sandstones of the overlying 

Toroweap Formation, and so they are mapped as one 

unit in Walnut Canyon area. However, careful field 

examination reveals that a truncation surface marked by 

vegetation in outcrop exposures typically separates 

Toroweap beds from the underlying Coconino 

Sandstone (Turner 2003). Within Walnut Canyon, the 

combined Coconino and Toroweap unit is 225 m (738 ft) 

thick (Rowlands et al. 1995). 

The Coconino Sandstone is the primary aquifer in the 

region. Local fractures, parting along bedding planes, 

and limestone dissolution allows precipitation to 

percolate through the Kaibab Formation to the 

underlying Coconino Sandstone recharging this regional 

aquifer (Paul Whitefield, NPS WACA, written 

communication November 30, 2005). 

Uplift of the Colorado Plateau in the Cenozoic Era and 

regional erosion removed most of the Mesozoic and 

Cenozoic rocks from the Walnut Creek area. Although 

the siltstones, mudstones, and sandstones of the Triassic 

Moenkopi Formation have been mostly eroded, they do 

outcrop locally, ranging in thickness from 0 to 120 m (0 

to 394 ft) (Rowlands et al. 1995). Patchy outcrops occur 

along the upthrown side of the Anderson Mesa normal 

fault. The Moenkopi also outcrops in narrow structural 

basins oblique to the Anderson Mesa Fault in Walnut 

Canyon. 

Tertiary and Quaternary basaltic lava flows locally cap 

the sedimentary strata. The Anderson Mesa Basalt caps 

Anderson Mesa immediately south of Walnut Canyon 

(fig. 3). Basaltic lava flows within the Lake Mary Graben 

are approximately 38 m (125 ft) thick, covered by 

Quaternary alluvium (Rowlands et al. 1995). Like the 

Kaibab Formation, these fractured basalts act as recharge 

zones for many local perched aquifers. 

Quaternary alluvial (stream) and lacustrine (lake) 

deposits are as thick as 23 m (75 ft) (Rowlands et al. 1995). 

Colluvial (slope) deposits of talus at the base of slopes 

occur along the downthrown sides of faults, in canyons, 

and along margins of lava flows. 

Faults and fractures that strike perpendicular to the 

trend of Walnut Canyon across Anderson Mesa and 

along the Lower Lake Mary shoreline are the dominate 

the geologic structures of the area (fig. 3). The major fault 

is the Anderson Mesa Fault - a normal fault that forms 

the southwest boundary of Anderson Mesa and the 

northeast boundary of the Lake Mary basin (Rowlands et 

al. 1995). 

Park History 

The earliest evidence of humans living in Walnut Canyon 

dates back to 4,000 B.C. (Hansen et al. 2004). However, 

the highest density of prehistoric people living in the area 

was from 600 A.D. to 1250 A.D. when a prehistoric 

farming culture flourished in the Flagstaff area (Hansen 

et al. 2004; http://www.nps.gov/waca/index.htm, 

accessed October, 2004). The Spanish named these 

people the Sinagua culture, a name taken from “Sierra 

Sinagua” meaning “mountain range without water” (NPS 

2003; Hansen et al. 2004; http://nps.gov/waca/index.htm, 

accessed October 2004). Although Noble (1991) refers to 

the “Sinagua Indians,” Sinagua is not the name of a tribe 

or clan, but refers to various archeological sites and 

objects found in this part of Arizona that have similar 

characteristics. How these people collectively perceived 

themselves and their neighbors, or what they called 

themselves is not known (http://www.nps.gov/waca, 

accessed October, 2004). 

The ancient farmers grew corn, squash, and beans above 

the Walnut Canyon rim. Ash and cinders from the 

eruptions of nearby Sunset Crater Volcano (the last 

eruption occurred about 1,000 years ago) enriched the 

soil, curbed evaporation, conserved soil moisture, and 

increased productivity of the Sinagua’s fields so that the 

regional population began to grow. People first moved 

down into the canyon about 1150 A.D. when they built 

most of the cliff dwellings that line the canyon walls. 

Although little water flows in Walnut Creek today 

because of two upstream dams, Walnut Creek once 

supported a rich variety of plants and animals (http:// 

nps.gov/waca, accessed October 2004). 

The Sinagua culture in Walnut Canyon thrived for about 

150 years, but around 1250 A.D., the Sinagua mysteriously 

abandoned the canyon. Archaeologists are not sure why 

the Sinagua people left, but probable causes include lack 

of precipitation, falling water tables, permanent water 

shortages, resource depletion, repeated crop failures, and 
4 NPS Geologic Resources Division 

rapidly expanding arroyo systems (Schroeder 1977; 

Rowlands et al. 1995; http://www.desertusa. com/ind1 

/du_peo_sin.html, accessed March 2007). Hopi oral 

histories tell of the Sinagua migrations 

(http://www.desertusa.com /ind1 /du_peo_sin.html, 

accessed March 2007; Noble 1991). 

The Walnut Canyon cliff dwellings are unique in that 

they are the only known such remains of the northern 

Sinagua culture. The site density in the monument 

averages almost 100 sites per square mile, compared with 

typical densities of 40 sites per square mile in other areas 

near Flagstaff (NPS 2003). About 300 rooms are scattered 

along both sides of Walnut Canyon. In 1885, James 

Stevenson of the Smithsonian Institution visited the area 

and noted, 

“The doors are large and extend from the ground up to 

a sufficient height to admit a man without stooping. 

The rooms are large and the walls are two to four feet 

thick. The fireplaces are in one corner of the room on 

an elevated rock, and the smoke can only escape 

through the door. The masonry compares favorably 

with the construction of the best villages in Canyon de 

Chelly. Many objects of interest were found in the 

debris around and in these houses. Matting, sandals, 

spindle whorls, and stone implements of various kinds 

abound.” 

 (Vandiver 1936, p. 2). 

Vandals and thieves removed almost all of the 

archaeological objects from the cliff dwellings described 

by Stevenson, and many of the cliff dwellings were 

broken down and destroyed prior to 1906 when the U.S. 

Forest Service first protected the area (Vandiver 1936). 

The dense concentration of prehistoric ruins, their 

exceptional state of preservation, and their unusual and 

highly scenic setting in sheltered alcoves, as well as the 

threat of imminent destruction by commercial looters 

and misguided tourists were key factors influencing the 

creation of Walnut Canyon National Monument (NPS 

2003). 

No large settlements of humans inhabited Walnut 

Canyon after 1250 A.D., but the surrounding landscape 

has been altered by historic and modern human activity 

such as logging, hunting, fire suppression, housing 

development, water impoundments, and road and utility 

construction. In 1973, the park installed a fences around 

protected ruins and prohibited livestock grazing. Grazing 

continues in areas adjacent to the monument and within 

the unfenced monument boundary (Hansen et al. 2004). 
 WACA Geologic Resource Evaluation Report 5 

Figure 1. Regional location map for Walnut Canyon National Monument. 
6 NPS Geologic Resources Division 

Figure 2 Trails and relief in Walnut Canyon National Monument. Map courtesy of the National Park Service, 

http://www.nps.gov/waca/planyourvisit/index.htm (Accessed March 2007).
 WACA Geologic Resource Evaluation Report 7 

 Walnut Canyon NM

 Anderson

 Mesa

Figure 3. Shaded relief map showing the Walnut Canyon National Monument area. The black arrow points to the escarpment of the 

Anderson Mesa Fault. Lake Mary lies in the graben formed by the fault. The north-south lineaments that cross Walnut Canyon and the 

northwest-southeast and northeast-southwest features are faults. The image was generated using 30 meter resolution Digital Elevation 

Model (DEM) data. Map courtesy of the U.S. Geological Survey, http://terraweb.wr.usgs.gov/projects/Flagstaff/ dem.html (Accessed 

March 2007). 
8 NPS Geologic Resources Division 

Figure 4. Cliff dwellings at Walnut Canyon National Monument constructed in an alcove within the Kaibab Formation beneath an 

overhanging ledge of limestone. Photo courtesy of the USGS; http://3dparks.wr.usgs.gov/walnutcanyon/html2/wc1650.htm (Accessed 

March 6, 2007). 
 WACA Geologic Resource Evaluation Report 9 

Period Formation/Unit General Lithology 

Alluvium Unconsolidated gravel, sand, silt deposits 

Quaternary Lacustrine deposits Fine- grained lake deposits 

Colluvium Unconsolidated gravel, sand, & basalt 

Regional Unconformity 

Triassic Moenkopi Fm Mudstone, siltstone, & sandstone 

Regional Unconformity 

Kaibab Fm. Dolomite, sandy limestone, cherty limestone 

Permian Toroweap Fm. & 

Coconino Sandstone Cross- bedded quartz sandstone 

Regional Unconformity 

Pennsylvanian/Permian Supai Group Not exposed in Walnut Canyon NM 

Figure 5. Generalized stratigraphic column for Walnut Canyon National Monument, Arizona. 
10 NPS Geologic Resources Division 

Geologic Issues 

A Geologic Resource Evaluation scoping session was held for Walnut Canyon National 

Monument on June 28–29, 2001, to discuss geologic resources, address the status of 

geologic mapping, and assess resource management issues and needs. The following 

section synthesizes the scoping results, in particular those issues that may require 

attention from resource managers. 

Since 1941, flow in Walnut Creek has been severely 

limited due to two upstream dams. Decreased flow has 

resulted in reduced sediment input, reduced streambed 

scouring, reduced recharge of springs and seeps, and a 

more static channel morphology. Changes in the 

geomorphic and hydrogeologic character of the canyon 

bottom and Walnut Creek have caused changes in the 

riparian habitat flanking the creek, which depends on a 

scoured channel, periodic flooding, and adequate 

groundwater. The riparian areas in Walnut Canyon 

provide an important element of the desired cultural 

landscape setting for the Sinagua cliff dwellings and 

enhances the natural viewshed from the primary visitor 

use areas. Ultimately, the riparian corridor significantly 

enhances habitat diversity, species richness, cultural 

resource integrity, and visitor experience (Whitefield 

2005). For these reasons, defining the integrated 

geomorphic and hydrogeologic response to decreased 

water flow in the canyon is the primary geologic issue 

facing Walnut Canyon National Monument. 

Rockfall 

Rockfall is a serious hazard in the rugged canyons of 

Walnut Canyon National Monument that can impact 

visitor and staff safety as well as park infrastructure. The 

Island Trail is the most popular trail at Walnut Canyon 

National Monument. It descends into a steep, rugged 

canyon allowing park visitors to hike in a natural 

environment and view ancient cliff dwellings. On 

November 30th and December 8th, 2007 two rockfalls 

damaged large sections of the Island Trail. The initial 

rockfall blocked the lower section of the trail and the 

much larger December 8th event took out large sections 

of a concrete stairway, steel handrails, and a bench. As a 

result the trail is closed to visitor use pending 

remediation (Greco 2008). 

The natural processes that formed the canyon are still at 

work and can sometimes produce hazardous conditions. 

Climate can be a primary driver behind hazards in 

Walnut Canyon as was the case with recent events. The 

weathering and erosion of material from slopes is 

seasonally controlled. Extreme mechanical weathering 

from freeze- thaw action during the winter months can 

account for a large portion of the debris moving down 

slope. During climatic extremes such as drought, heavy 

snow pack or extreme rainstorms, the erosion cycles can 

be accelerated. In times of drought, excess debris builds 

up, then during rainstorms events or snow melt, the 

amount of material flushed can increase substantially 

(Greco 2008). 

The 2007 rockfall events were not unique in Walnut 

Canyon National Monument. Rockfall is a natural 

occurance and a long history of past rockfalls is evident 

in the talus and large boulders scattered throughout the 

canyon. Scars on the canyon walls likewise identify 

where large chunks of rock have previously fallen. Larger 

size rockfalls occur infrequently and are only addressed 

when they impact park infrastructure or threaten visitor. 

Smaller rockfalls occur much more frequently and 

usually go unreported. 

Geomorphology and Hydrogeology 

Walnut Canyon National Monument contains 13 linear 

km (8 linear mi) of Walnut Canyon. The canyon bottom 

is narrowly- incised into the Coconino Sandstone where 

the Walnut Creek drainage meanders northeastward 

through coarse- grained stream terrace deposits and 

talus blocks from the canyon walls. Water catchment 

basins of various sizes, scoured into the Coconino 

Sandstone, provide important water sources for wildlife. 

Groundwater from numerous fractures and bedding 

planes seeps from the steep canyon walls and tributary 

canyons (Chronic 1983; NPS 2003; Whitefield 2005). 

The Walnut Canyon watershed drains an area of about 

108,800 acres or 170 square miles (440 sq km). 

Approximately 75%, or 83,200 acres, 130 square miles, 

(337 sq km) of the Walnut Creek watershed lies upstream 

of the monument to the south and west in the Coconino 

National Forest. Walnut Creek headwaters originate in 

the Mormon Mountain- Mormon Lakes area more than 

32 km (20 mi) south of the monument. Prior to the first 

upstream dam construction in 1904, anecdotal and 

photographic evidence suggests that Walnut Creek was 

once an ephemeral stream with an open, rocky bed 

maintained by seasonal flooding (Rowlands et al. 1995). 

Reliable flows typically occurred early each year during 

the seasonal spring snowmelt. Less predictable flows 

occurred during the summer and fall thunderstorm 

season. Today, dense stands of invasive, hearty upland 

woody vegetation choke the bottom of Walnut Creek 

(Rowlands et al. 1995). 

Wetlands, floodplains, and riparian habitats covering 

about 90 acres within Walnut Canyon National 

Monument are restricted to the narrow canyon bottom 

and a number of perennial seeps found in the tributary 

canyons on the south side of the monument. Riparian 

vegetation includes a tree canopy of box elder, Arizona 

walnut, narrow- leaf cottonwood, Rocky Mountain 

juniper, ponderosa pine, Douglas fir, and Gambel oak. 
 WACA Geologic Resource Evaluation Report 11 

The understory contains red osier dogwood, New 

Mexico locust, wild grape, Arizona wild rose, fragrant 

sumac, and snowberry. The riparian flora includes more 

than 150 species, or approximately one- third of the total 

flora variety within the monument (Hansen et al. 2004; 

Whitefield 2005). Riparian habitats are a vital component 

to the Walnut Canyon ecosystem. 

Three dams built between 1885 and 1941 affected the 

geomorphology and the riparian corridor within the 

greater Walnut Canyon drainage. A masonry dam 

constructed downstream (eastern boundary of the 

monument) dammed lower Walnut Creek between 1883 

and 1886. The reservoir supplied water to the Santa Fe 

Railway (Rowlands et al. 1995; NPS 2003; Whitefield 

2005). The railway discontinued use of the reservoir in 

1904, and in 1934, stockmen from the Kellum Ranch 

blasted the northern end of the dam to allow any 

accumulated water to drain out (Rowlands et al. 1995). 

In 1990, the owner of the Santa Fe Dam repaired the 

dam, briefly impounding runoff during March and April 

1991 (NPS 1992; Rowlands et al. 1995). Creek flow is 

ephemeral, but the dam still impounds some water after 

major flows. During rare flood events, the canyon 

bottom is totally inundated for about 1.6 km (1 mi) 

upstream of the dam. Flooding transports alluvium down 

the canyon which collects behind the dam. These fine 

sediments now mantle the canyon and have essentially 

filled in the “reservoir.” 

In 1904, construction of the first of two upstream dams 

created Lower Lake Mary to provide water for sawmills 

in Flagstaff. The lake was named for the oldest daughter 

of Timothy A. Riordan of the Arizona Lumber and 

Timber Company. This earthen dam significantly 

disrupted seasonal water flow through the canyon. The 

dam spanned a local fault zone and water infiltrated the 

porous and fractured bedrock along the fault. 

A second earthen dam, built in 1941, created Upper Lake 

Mary - an important public water supply for Flagstaff. 

This second dam effectively ceased regular flow of 

Walnut Creek. While long- term hydrological data do 

not exist for Walnut Creek, research suggests that the 

impoundments have altered the frequency of flows in 

Walnut Canyon and have probably altered the 

magnitude and duration of peak flooding (Rowlands et 

al. 1995). Prior to upstream impoundment, winter and 

spring flows through Walnut Canyon occurred annually. 

Now, these flow events occur once every nine years on 

average. Summer flows from the Upper Lake Mary and 

Lower Lake Mary reservoirs have been completely 

eliminated through Walnut Canyon. Summer flows in 

Walnut Creek only arise from unusually heavy local 

runoff from canyon slopes and from tributaries below 

Lower Lake Mary. Estimates of annual surface water 

runoff into Walnut Canyon suggest a flow volume 

reduction from 360 million to 31 million cubic meters 

(290,000 to 25,000 acre- feet) due to the presence of the 

two upstream reservoirs (Rowlands et al. 1995). Yet to be 

fully understood are changes to stream channel scouring, 

sediment transport, alluvial terrace formation, and local 

spring and seep recharge, resulting from creek 

impoundment are (Rowlands et al. 1995; NPS 2003; 

Whitefield 2005). 

In 1993, heavy and prolonged rains over Arizona caused 

the most widespread and severe flooding since the turn 

of the Twentieth Century (Rowlands et al. 1995). For 

eight weeks, floodwaters flowed through Walnut 

Canyon. Ephemeral drainages without dams are subject 

to twice- yearly seasonal runoff and are able to maintain 

open channels and support riparian plant species, such as 

willows. A true riparian ecosystem may have existed in 

Walnut Canyon prior to the 1904 dam construction 

(Rowlands et al. 1995). 

The extent and volume of groundwater collection and 

movement within the Walnut Canyon drainage system is 

not known. The Coconino Sandstone is the regional 

aquifer beneath Walnut Canyon National Monument. 

The local water table of this aquifer is at least 180 m (600 

ft) below the canyon floor with no potential for surface 

discharge. Fractures in the bedrock and dissolution of 

the limestone in the Kaibab Formation allow recharge of 

the numerous seeps at the base of the canyon walls in 

response to local precipitation. The seeps may flow 

continuously in wet years but remain dry during 

droughts. Persistent drought conditions since 1996 have 

resulted in nearly dry seeps along the base of Walnut 

Canyon (Whitefield 2005). 

Faulting in the Kaibab Limestone, and porous Coconino 

Sandstone contributes to the recharge and confinement 

pathways in the Walnut Creek terrace deposits. 

Hydrogeologic characteristics in the monument 

favorable to local recharge include (Whitefield 2005): 

• Up to 60 m (200 ft) of highly porous and permeable 

Kaibab limestone allowing precipitation to rapidly 

percolate to the underlying Coconino Sandstone 

aquifer. Some groundwater flows horizontally along 

the contact between the formations, whereas some is 

confined and flows laterally through local fractures 

and bedding planes. 

• The Anderson Mesa Basalt caps Anderson Mesa and 

serves as a recharge zone for many small perched 

aquifers. 

• Sedimentary strata and basalt flows dip gently to the 

northeast, directing lateral groundwater flow toward 

the southern canyon walls. This flow may be 

responsible for the seeps in the sandstone bedding 

planes at the base of the canyon. 

• At least three faults as well as several minor faults and 

fractures strike perpendicular to Walnut Canyon. 

Although a considerable volume of groundwater is 

immediately directed to the deep Coconino Aquifer, 

some groundwater may move laterally through the 

faults and into the canyon. 

• The narrow Walnut Canyon, incised into sandstone 

bedrock, contains shallow flanking terraces of coarse 

alluvium. Groundwater seeping from bedrock could 

collect in shallow lenses within the terrace deposits. 
12 NPS Geologic Resources Division 

• Precipitation or intermittent surface flows within the 

local watershed below Lower Lake Mary reservoir 

may directly recharge the terrace deposits. 

Restoring seasonal water flows of Walnut Creek is a 

necessary step toward total restoration of the riparian 

corridor within Walnut Canyon. It is unlikely that the 

upstream dams will be removed, but in 2001, the National 

Park Service, Forest Service, and City of Flagstaff agreed 

to cooperatively investigate methods to increase the 

probability of flood flows from Lower Lake Mary 

reservoir in order to improve the inner canyon 

environment (Whitefield 2005). Assessing stream 

channel changes over time and the potential for shallow 

groundwater(perched aquifers) within the corridor is 

fundamental to riparian ecosystem management. 

Understanding groundwater flow within the canyon is 

the first step to correlating upland vegetation and soil 

conditions, intermittent flows in tributary drainages, 

reservoir levels, and downstream groundwater 

fluctuations with the status of the canyon riparian 

corridor. 

Rowlands and others (1995) characterized the vegetation 

changes in Walnut Canyon due to upstream 

impoundments, but persistent research needs include 

field studies to characterize the changes to channel 

morphology and the occurrence of shallow groundwater 

within the inner canyon stream terrace deposits (Paul 

Whitefield, NPS Natural Resource Specialist, written 

communication, March 29, 2007). Recommended 

research include (Whitefield 2005): 

• Re- measure twelve stream profiles (Phillips 1990), 

describing the composition and geomorphology of the 

drainage terrace and channel deposits and compare to 

1990 measurements. 

• Using hand- held equipment, complete a geophysical 

investigation to determine the position of the 

groundwater table, to measure the thickness of stream 

terrace deposits, and to determine the subsurface 

contact with Coconino sandstone bedrock. 

• If the geophysical investigation confirms the presence 

of shallow groundwater, install shallow groundwater 

monitoring wells. 

• Develop a preliminary conceptual model to explain the 

hydrogeologic function and potential groundwater 

recharge within the canyon watershed. 

Secondary Geologic Issues 

Volcanic Hazards 

Walnut Canyon National Monument lies south of the 

San Francisco Volcanic Field, which covers about 4,700 

sq km (1,800 sq mi) of northern Arizona (fig. 6). The 

volcanic field has produced more than 600 volcanoes in 

its 6 million year history (Priest et al. 2001). Humphreys 

Peak, Arizona’s highest mountain at 3,850 m (12,633 ft), is 

the only stratovolcano in the field. Stratovolcanoes are 

cone- shaped volcanoes (e.g., Mt. Rainier), that often rise 

to a central peak and form by countless eruptions over 

hundreds of thousands of years. 

Most of the volcanoes in the San Francisco Volcanic 

Field are basaltic cinder cones. In contrast to 

stratovolcanoes, cinder cones are usually smaller, less 

than 300 m (1,000 ft) high, and form relatively quickly 

(months to years). The cones form when basaltic lava 

erupts as an upward spray, or lava fountain, quickly cools 

and falls to the ground as dark volcanic rock fragments 

or cinders. Large fragments are volcanic bombs. A cinder 

cone builds from this accumulated volcanic debris. 

(Priest et al. 2001). 

The youngest cinder cone in the San Francisco Volcanic 

Field is Sunset Crater, which erupted between 

approximately 1080 and 1150 A.D. (http://www.volcano. 

si.edu/world/volcano.cfm?vnum=1209- 02, accessed 

March 25, 2007). 

The San Francisco Volcanic Field is somewhat 

anomalous in that typically volcanoes are located near 

tectonic plate boundaries, rather than well within the 

interior of the North American Plate. Some evidence 

suggests that a site of localized melting, or “hot spot,” is 

fixed deep within Earth’s mantle, and as the North 

American Plate moves slowly westward over this 

stationary source of magma, eruptions produce 

volcanoes that are strung out progressively eastward 

(Priest 2001). 

Other observations note that the vents associated with 

the Sunset Crater are aligned along the northeasttrending Colorado Lineament, a major fracture zone in 

the lithosphere (Luedke and Smith 1991), suggesting a 

possible structural control to the eruptions rather than a 

stationary hot spot. For at least the last 15 million years, 

volcanic eruption have migrated to the northeast 

(Luedke and Smith 1991; Scott 2004). 

Although no eruptions have occurred in the last 1,000 

years, volcanic activity could continue in the San 

Francisco Volcanic Field (Luedke and Smith 1991; Priest 

et al. 2001). However, predicting the next eruption and 

possible impacts from such an event on Walnut Canyon 

National Monument is difficult because the average 

interval between periods of volcanic activity is several 

thousand years. Based on past patterns, future eruptions 

are likely to be small and occur in the eastern part of the 

field. Nevertheless, ash fall from an eruption could have 

a large but short- term effect on Walnut Canyon 

National Monument (Priest et al. 2001). 

Seismicity 

Although a number of normal faults may have been 

active in the Walnut Creek area during Quaternary time, 

only the Anderson Mesa fault and the much smaller 

Marshall Lake fault, which are located south of the 

monument, display evidence of significant late 

Quaternary activity. Rockfall, infrastructure damage, and 

flash flooding are potential hazards that could result 

from renewed seismic activity in the area. 
 WACA Geologic Resource Evaluation Report 13 

Flash Floods 

Flash flooding in the canyon has been identified as a 

hazard in Walnut Canyon, especially for monument staff, 

researchers, and visitors. Intense rainfall events in the 

Walnut Creek drainage may quickly trigger flash floods 

from tributary canyons. If either of the upstream dams 

were to fail catastrophically, flash floods would inundate 

Walnut Canyon. Both dams are located along the Lake 

Mary Fault. Disaster planning and education for flash 

flooding events could be an important safety undertaking 

for resource management at Walnut Canyon National 

Monument. 

Fossil Theft 

Marine life flourished during the Permian Period, and 

the fossiliferous limestone in the Kaibab Formation 

reflects this abundance (fig. 7). Gastropods (snails), 

pelecypods (clams), scaphopods, cephalopods, 

brachiopods, trilobites, worm tubes, and shark’s teeth in 

the limestone characterize the marine environment at the 

time. The fossils can add a significant, visual element to 

the interpretation of the geologic history of the 

monument (Vandiver 1936; Santucci and Santucci 1999). 

Fossil molds exposed in the Kaibab Formation along the 

Island Trail to the cliff houses are mostly hollow, plumsized pits left when groundwater dissolved the fossilized 

shells. The invertebrate fossils within the Kaibab 

Formation have little market value as they are small, and 

often fragments of shells. Also, they are not easily 

removed from the hard limestone. 

Paleontological resources are believed to receive 

adequate protection by Walnut Canyon staff (NPS 2003). 

Visitors are allowed only on the 1.4- km (0.9- mi) Island 

Trail and the Rim Trail limiting access to invertebrate 

fossils in the Kaibab Formation. Federal law prohibits 

fossil collecting in units of the National Park System 

without a research permit regulations at 36 CFR § 2.1 (a) 

(iii). The monument has documented a few incidents of 

illegal removal of fossils. Although the theft of marine 

fossils does not seem to be a serious management 

problem at this time it is essential that resource 

management continue to protect this non- renewable 

resource (NPS 2003; Paul Whitefield, NPS Natural 

Resource Specialist, written communication, March 29, 

2007). 

Potential Aquifer Contamination 

As discussed above, two principal aquifers underlie 

Walnut Canyon National Monument (Bills et al. 2000; 

Thomas 2003). The upper is a local shallow aquifer 

perched in the Kaibab Formation and the upper part of 

the Coconino Sandstone. Local precipitation and runoff 

recharge this aquifer and it discharges water to several 

springs and seeps near the bottom of Walnut Canyon. 

The second principal aquifer is the regional Coconino 

Aquifer. The Coconino Aquifer is the source of water for 

most uses in the Flagstaff and Walnut Canyon areas. In 

the vicinity of Walnut Canyon, depth to the water table is 

about 457 m (1,500 ft) below the land surface (Bills et al. 

2000). Regional groundwater flow is to the northeast 

(Appel and Bills 1980). 

The well at monument headquarters extracts 

groundwater from the Coconino Aquifer from a depth of 

612 m (2,007 ft). Risk of contamination in the Coconino 

Aquifer is low due to the depth to groundwater, slow 

groundwater movement, and the natural attenuation of 

contaminants in the aquifer (NPS 2003; Thomas 2003). 

Under current levels of extraction within the watershed, 

there also is little threat of aquifer depletion (NPS 2003). 

The primary threats to the water quality in Walnut 

Canyon are from grazing sheep and cattle on the south 

side of the canyon and from facilities, such as 

maintenance shops and sewage lagoons (Thomas 2003). 

Water resources vulnerable to contamination from these 

sources include the ephemeral streams, perched 

groundwater lenses, and the local shallow aquifer. Future 

impacts to both the regional and local aquifer, however, 

may come from residential or commercial development 

of the Walnut Canyon watershed (NPS 2003; Thomas 

2003). The city of Flagstaff annexed all the lands to the 

north and west boundary of Walnut Canyon National 

Monument. Annexation includes a relatively large area 

contiguous to the canyon rim and tributary canyons west 

of the monument. Urban development of these areas 

could significantly increase non- point source pollution, 

such as storm sewer runoff, vehicular residue (oil, grease, 

battery acid and fluids,) fertilizers, herbicides, and 

pesticides. 
14 NPS Geologic Resources Division 

Figure 6. San Francisco Volcanic Field. Many of the more than 600 vents, which have erupted in the area during the past 6 million 

years, can be seen on this digital elevation model (DEM). Lava flows are flat lobate features near vents. The northeast-trending Mesa 

Butte Fault and Doney Fault are also labeled. Flagstaff lies at the south-central edge of the volcanic field. Picture is from Priest and 

others (2001), available at http://geopubs.wr.usgs.gov/fact-sheet/fs017-01/, (Accessed March 2007). 
 WACA Geologic Resource Evaluation Report 15 

Figure 7. Representative sample of the fossiliferous limestone in the Kaibab Formation. Long tapered shells are scaphopods; circular 

shell fragments are brachiopod valves. This sample is from the Coconino Plateau, but not specifically from Walnut Canyon National 

Monument. Photo is courtesy of Northern Arizona University and found at http://oak.ucc.nau.edu/llc7/Photo%20Albums/Geology/ 

slides/Kaibab%20Limestone %20Marine%20Fossils.html, (Accessed March 2007). 
16 NPS Geologic Resources Division 

Geologic Features and Processes 

This section provides descriptions of the most prominent and distinctive geologic features 

and processes in Walnut Canyon National Monument. 

Geologic features at Walnut Canyon National 

Monument range in scale from fossil fragments 

embedded in limestone to faulting visible from satellite 

imagery. Processes that formed these features are equally 

diverse, including aeolian processes that formed ancient 

sand dunes, regional tectonic uplift, and erosion that 

carved Walnut Canyon. 

Geomorphic Features 

Walnut Canyon is the dominant geologic feature in 

Walnut Canyon National Monument (fig. 8). 

Downcutting of Walnut Canyon by Walnut Creek has 

occurred over the last five million years, carving a steepwalled canyon averaging about 350 feet (107 m) deep 

(Chronic 1983; http://3dparks.wr.usgs.gov/ 

walnutcanyon/html/wc1640.htm, accessed March 2007). 

Walnut Creek incised into bedrock analogous to the 

Colorado River at the Grand Canyon – downcutting 

accelerated by regional uplift. Uplift of the Colorado 

Plateau began about 65 Ma at the beginning of the 

Tertiary Period, and periods of uplift followed into the 

late Tertiary. Continued uplift of the Colorado Plateau 

forced Walnut Creek to cut into the underlying bedrock 

while maintaining its original meander pattern 

(Rowlands et al. 1995). A stream that inherits its channel 

from a previous erosion cycle cuts into bedrock by 

overprinting the pre- existing channel morphology 

becoming entrenched (fig. 8). 

Today, Walnut Creek is an underfit stream or a stream 

that appears too small to have eroded the canyon in 

which it flows. However, the flow in Walnut Creek was 

probably much greater during the wetter Pleistocene 

Epoch more than 10,000 years ago when precipitation 

and runoff on the Coconino Plateau were much higher 

than today (Rowlands et al. 1995). 

Sharp, angular turns in Walnut Creek correspond with 

joint orientations in the walls of the canyon indicating a 

marked influence of pre- existing geologic structures on 

the geomorphology of the canyon. Deformation 

associated with large, north- south trending regional 

faults may have influenced joint orientations in Walnut 

Canyon (fig. 3) (Henkle 1976; Rowlands 1995). 

Geomorphic processes have reworked coarse- grained 

colluvium and eroded fine- grained sand from the 

Coconino Sandstone into a variety of depositional types. 

Deposits include upland terrace alluvium, coarse channel 

and channel bar deposits, dunes, and scour holes, 

establishing distinctive vegetation patterns based on 

sediment and water availability (Rowlands et al. 1995). 

For example, Douglas fir, Gambel oak, and snowberry 

dragon sage prefer upland terrace deposits, whereas 

Arizona rose, New Mexico locust, and red osier 

dogwood thrive in streambed and channel bar deposits. 

Sedimentary Features 

The buff- colored Coconino Sandstone forms the walls 

of the steep lower portion of Walnut Canyon. Sweeping 

cross- beds of aeolian sandstone are the primary 

sedimentary features in this unit (fig. 9). Cross- bedding 

preserves migrating foreset dunes that formed roughly 

275- 280 Ma near an ancient Permian shoreline (Peterson 

1980). The dune field covered northern Arizona, 

southern Utah, and northwestern New Mexico at a time 

when the landscape and climate were similar to today’s 

Sahara desert. Other sedimentary features found in the 

Coconino Sandstone include raindrop impressions, wind 

ripple marks, and sand avalanches that once slid off the 

over- steepened front of a migrating dune. 

The fossiliferous marine limestone of the Kaibab 

Formation contrasts with the underlying, aeolian crossbedded Coconino Sandstone (fig. 9). The Kaibab 

Formation outcrops in the cliffs of the upper third of 

Walnut Canyon. Thick, erosion- resistant, gray limestone 

ledges separate slopes of soft, thinly interlayered, silty 

limestone or limy sandstone (fig. 4). Limestone in the 

Kaibab indicates an ancient marine regression into the 

region. During this time, sea level fluctuated cyclically. 

When sea level rose, shallow, open marine conditions 

prevailed supporting a diverse marine ecosystem that 

included brachiopods, sponges, and other marine 

invertebrates. When sea level fell, faunal diversity 

decreased and near- shore limy sand and silt 

accumulated. These contrasting depositional 

environments became the alternating limestone ledges 

and carbonate sandstone slopes exposed in Walnut 

Canyon. 

Chert nodules are abundant in some of the limestone 

layers. These nodules formed from sponge spicules, 

skeletal elements of sponges composed of minute 

needles of silica. When the sponges died, these siliceous 

spicules accumulated on the ocean floor, and with 

subsequent burial and pressure from overlying sediment, 

the silica formed nodules of chert. Chert (flint) formed 

from spicules is hard and dense and was widely used for 

various tools and spear points by early Native Americans 

throughout the western United States. However, there is 

no evidence that the Sinagua of Walnut Canyon used 

chert. This could be due to vandalism and theft of the 

Sinagua cultural resources at Walnut Canyon prior to 

protection by the federal government. 
 WACA Geologic Resource Evaluation Report 17 

Tectonic Deformation 

Sedimentary features, such as sand dunes, result from 

processes that focus on individual grains or fragments of 

material whereas tectonic features form through 

processes that deform the crust and lithosphere. Plate 

tectonic processes involve plates separating from each 

other along continental and oceanic rifts, sliding past 

each other along transverse margins, and colliding into 

each other forming mountain chains and subduction 

zones (fig. 10). As plates collide, one plate may subduct 

beneath the other and create a deep trench in which vast 

amounts of sediments accumulate. These sediments may 

combine with bits of oceanic crust and small landmasses 

such as islands and island arcs to form an accretionary 

wedge between the two plates. If this wedge accretes to 

the edge of the overriding plate, the continent grows in 

size. 

Throughout the middle Paleozoic Era and into the 

Mesozoic Era, western North America had been an 

active collisional margin where dense oceanic crust 

subducted beneath the lighter continental crust of the 

North America lithospheric plate. Compressive forces 

produced thrust faulting and large- scale folding of 

originally horizontal sedimentary geologic units. 

Remnants of these thrust faults and folds appear in 

mountain ranges west of the Colorado Plateau province. 

About 20 Ma subduction off the southwestern coast of 

North America ceased and the lithospheric plates began 

to slide past one another, generating strike- slip faulting 

culminating in the San Andreas fault system of California 

(Pallister et al. 1997). Strike- slip faulting and high heat 

flow beneath the southwestern region of the United 

States resulted in crustal extension. Large crustal blocks 

dropped down along high- angle normal faults, creating 

grabens (structural basins) adjacent to relatively uplifted 

blocks (horsts) forming mountain ranges. This type of 

regional faulting produced the characteristic topography 

of the Basin- and- Range physiographic province of the 

western United States. 

The Colorado Plateau remained relatively stable 

throughout this tectonic deformation to the west. The 

crustal extension that affected parts of Utah, Nevada, 

Arizona, and New Mexico did not significantly deform 

the interior of the Colorado Plateau. However, normal 

faulting did occur along the margins of the province. 

The Anderson Mesa fault is a typical structure generated 

by Basin- and- Range extensional faulting. This fault is 

the most prominent feature in the rectilinear pattern of 

lineaments that crisscross the Coconino Plateau (fig. 3). 

The lineaments shown on figure 3 are fractures and 

normal faults controlled by deep- seated, Precambrian 

crustal structures that have been periodically reactivated 

throughout geologic time. Located south of Walnut 

Canyon National Monument, the Anderson Mesa fault 

follows a trend oriented approximately 65 degrees 

northwest along Upper Lake Mary and Lower Lake 

Mary before striking due north along the north- south 

trending part of Walnut Canyon (Rowlands et al. 1995). 

Topographic displacement along the Anderson Mesa 

fault is 60 m (197 ft) (Rowlands et al. 1995). Many smaller 

faults that postdate the Anderson Mesa fault strike 

parallel to the main fault and delineate the graben later 

forming Upper and Lower Lake Mary (fig. 3) (Rowlands 

et al. 1995). 

Numerous joints and fractures occur in Walnut Canyon 

and may have influenced the drainage pattern of Walnut 

Creek (Rowlands et al. 1995). North- south joint 

orientations probably reflect the trends of larger faults in 

the region. Joints and fractures affect the hydrogeologic 

system of the area. The highly fractured rocks locally 

transmit from 10 to 50 times as much groundwater as do 

adjacent, unfractured rocks of the same unit. 

Fossils 

The brachiopod Dictyoclostus is the most common fossil 

exposed along the Island Trail. Other fossils include 

spiral impressions of snails and molds of small clams 

(Chronic 1983). Several molds of brachiopod fossils are 

scattered along the back wall of the cliff dwellings. 

Invertebrate fossils from the Kaibab Formation in 

Walnut Canyon National Monument and the 

surrounding area include bryozoans, mollusks, 

brachiopods, trilobites, sponges, echinoderms, and 

worm tubes (table 1) (Santucci and Santucci 1999). Teeth 

from a variety of sharks appear in the Kaibab including 

Sandalodus, Deltodus, Symmorium, Petalodus, and 

Orrodus and phyllodont tooth plates. 

The dune deposits of the underlying Coconino 

Sandstone yield fewer fossils than the marine limestone 

in the Kaibab Formation. Low diversity vertebrate and 

invertebrate trace fossils are reported from within the 

Coconino Sandstone, but not from Walnut Canyon 

National Monument (Santucci and Santucci 1999; 

Middleton et al. 2003). Trace fossils in the Coconino 

include trails, tracks, burrows, borings, tubes, tunnels or 

other impressions in the sediments caused by animal 

activity. 
18 NPS Geologic Resources Division 

Table 1. Invertebrate fossils from the Kaibab Formation in Walnut Canyon NM area 

Phylum Class Genus sp./other 

Baylea sp 

Bellerophon deflectus 

Euomphalus sp 

Euphemites sp 

Goniasma sp 

Murchisonia sp 

Naticopsis sp 

Pennotrochus arizonensis 

Soleniscus sp 

Gastropoda 

Busyconids 

Allorisma sp 

Astarella sp 

Aviculopecten kaibabensis 

Dozierella sp 

Edmondia sp 

Gramatodon politus 

Janeia sp 

Kaibabella curvilinata 

Myalina sp 

Myalinella adunca 

Nuculana sp 

Nuculopsis sp 

Palaeonucula levatiformis 

Parallelodon sp 

Permophorous albequus 

Pleurophorus albequus 

Schizodus texanus 

Solemya sp 

Pelecypoda 

Solenomorpha sp 

Scaphalopoda Plagioglypta canna 

Aulometacoceras sp 

Metacoceras unklesbayi 

Stearoceras sp 

Mollusca 

Cephalopoda 

Tainoceras sp 

Chonetes sp 

Composita arizonica 

Dictyoclostus sp 

Marginifera sp 

Peniculauris bassi 

Quadrochonetes kaibabensis 

Brachiopoda 

Rugatia paraindica 

Anisopyge sp Arthropoda Trilobita Ditomopyge sp 

Annelida Worm tubes 

Bryozoa Fragments 
 WACA Geologic Resource Evaluation Report 19 

Figure 8. Walnut Canyon, Walnut Canyon National Monument. The meander pattern of the canyon reflects the entrenched meander pattern 

of Walnut Creek. Photo courtesy of the U.S. Geologic Survey, http://3dparks.wr.usgs.gov/walnutcanyon/html/wc1640.htm, (Accessed March 

2007). 
20 NPS Geologic Resources Division 

Figure 9. Cross-bedded Coconino Sandstone, Walnut Canyon National Monument. Overlapping sets of cross-beds denote migrating sand 

dunes similar to active processes today in modern dune fields. Photo courtesy of http://geoweb.tamu.edu/RGallery/zion2003/six/6i.html, 

(Accessed March 2007). 
 WACA Geologic Resource Evaluation Report 21 

Figure 10. Schematic of converging and diverging lithospheric plates according to plate tectonic theory. 
22 NPS Geologic Resources Division 

Map Unit Properties 

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

Evaluation digital geologic map of Walnut Canyon National Monument. The 

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

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

information in this table. More detailed map unit descriptions can be found in the help 

files that accompany the digital geologic map or by contacting the National Park Service 

Geologic Resources Division. 

The following Map Unit Properties Table identifies 

specific properties of the different geologic map units 

that may be useful for resource management decision 

making. Geologic features and processes often occur in 

or can be restricted to a particular stratigraphic unit 

(group, formation, or member). This table ties together 

the geologic features and processes with the properties 

of the geologic units presented on the accompanying 

digital geologic map. 

Source data for the GRE digital geologic map are from: 

Raucci, J., Blythe, N., Ort, M., and Manone, M. 2003. 

Geologic Map of the Greater Walnut Canyon National 

Monument Area. Scale 1:12,000. Northern Arizona 

University. Unpublished digital map. 

For a detailed list of references used in the development 

of this source map please refer to the help file that 

accompanies the digital geologic map. Digital geologic 

map data are included on the attached CD and are also 

available on the Web (http://www.nature.nps.gov/ 

geology/inventory/gre_publications.cfm). 

The Map Unit Properties Table presents the 

stratigraphic column and an itemized list of features per 

geologic unit. The table includes several properties 

specific to each unit in the stratigraphic column 

including age, map unit symbol, unit description, 

topographic expression of the unit, erosion resistance, 

paleontologic and cultural resources, hazards, and a 

miscellaneous column. 
Map Unit Properties Table 

Age Map Unit (symbol) Unit Description Topographic Expression Erosion Resistance Paleontological Resources Cultural Resources Hazards Other 

Alluvium 

(Qal) 

Unconsolidated fluvial deposits; thickness to 75 ft (23 m) Canyon bottom Low Locally perched water table 

Lacustrine 

(Ql) Fine- grained lake deposits Canyon bottom Low Limited exposures 

Colluvial 

(Qc) 

Unconsolidated deposits at the base of the canyon walls; maximum thickness 148+ feet (45+ m) 

Base of canyon 

walls High Limited exposures 

Basalt 

colluvium 

(Qbc) 

Unconsolidated basalt deposits at the base of 

the canyon walls 

Base of canyon 

walls High 

None None documented None 

Limited 

exposures 

QUATERNARY

Basalt 

(Qb) 

Basalt of Lower Lake Mary flow; not in monument NA NA NA NA NA Not exposed in monument 

TERTIARY Volcanic rocks (Tb) Basalt from the Anderson Mesa flow; lava flows are about 125 ft (38 m) thick within the Lake Mary Graben & are covered by Quaternary alluvium; not in monument. Caps Anderson Mesa, south of WACA NA NA NA NA Not exposed in monument 

LOWER 

TRIASSIC Moenkopi Fm (TRm) 

Reddish- brown mudstone, siltstone, & sandstone. Mostly eroded from area; present only in patchy outcrops along the upthrown side of the Anderson Mesa fault, in the Marshall Lake Graben, & in narrow grabens in Walnut Canyon; thickness from 0- 394 ft (0- 120 m) 

Limited exposures; present in low topographic areas 

Siltstone & mudstone is less resistant to erosion than the sandstone layers 

Amphibian & reptile tracks found to the north in Wupatki National Monument 

None documented None documented Limited exposures 

Kaibab Fm 

(Pkf) 

Gray, silty dolomite; sandy limestone; fossiliferous & cherty limestone; 364 ft (111 m) thick 

Caprock of canyon; ledges of dolomite & limestone separated by slopes or recesses of silty limestone or limy sandstone 

Resistant dolomitic limestone ledges; alcoves eroded into less resistant sandy limestone interlayers 

Abundant marine invertebrate fossils: gastropods, pelecypods, cephalopods, brachiopods, scaphopods, trilobites, sponges, echinoderms, worm tubes; variety of shark’s teeth 

Cliff dwellings built in less resistant, recessive layers between resistant limestone ledges 

Rockfall potential exists where Kaibab may collapse into underlying, less resistant layers 

Vertical fractures parallel to canyon; infrastructure & park buildings developed on Kaibab caprock 

LOWER 

PERMIAN 

Coconino 

Sandstone 

(Pc) 

Light colored, fine - grained, well- sorted, rounded quartz sandstone, highly crossstratified, exposed in canyon walls below Kaibab Formation; includes the overlying cross- bedded sandstone of the Toroweap Fm; 738 ft (225 m) thick 

Forms steep cliffs in lower third of Walnut Canyon 

Resistant to erosion but permeable to ground water 

No vertebrate or invertebrate trace fossils in monument; three trace fossil species of Chelichnus

(caseid- like reptile tracks) found outside of monument 

None documented Potential rockfall Aeolian sandstone; aquifer 
24 NPS Geologic Resources Division 

Geologic History 

This section highlights the map units (i.e., rocks and unconsolidated deposits) that occur 

in Walnut Canyon National Monument and puts them in a geologic context in terms of 

the environment in which they were deposited and the timing of geologic events that 

created the present landscape. 

The oldest rocks exposed in Walnut Canyon National 

Monument are Upper Paleozoic (Permian), about 275 

million years old (fig. 11). The geologic history of the 

southwestern United States is millions of years older. In 

Grand Canyon National Park to the north, the Elves 

Chasm pluton outcrops and is the oldest rock unit found 

in the southwestern United States at 1,840 million years 

old. (Pallister et al. 1997; Karlstrom et al., 2003). 

During the Precambrian, the Southwest may have looked 

like the western Pacific today with numerous volcanic 

belts separated by seas (Hoffman 1989; Pallister et al. 

1997). The southwestern coastline of North America 

paralleled the present border of Wyoming and Colorado. 

As crustal plates collided, volcanic belts, or island arcs 

developed and accreted terrane to the margins of North 

America in the process of continental growth. Through 

this process of accretion, most of Arizona was added to 

the North American continent by 1.4 billion years ago. 

In Arizona a major unconformity, representing 

approximately 800 million years of missing geologic 

history, separates the Precambrian units from 

Cambrian- age units (fig. 11). Cambrian rocks in Arizona 

record a major advance of the sea into the area about 520 

Ma. Throughout the Paleozoic Era, epicontinental seas 

advanced (transgressed) and retreated (regressed) 

depositing thick layers of limestone and sandstone on 

the sea floor. 

Permian Period 

Towards the end of the Paleozoic, landmasses were 

becoming tectonically sutured together to form a 

“supercontinent” called Pangaea. Approximately 275 Ma 

the Permian equator on the western margin of Pangaea 

was oriented southwest- northeast through modern 

Wyoming and eastern Utah (Biek et al. 2000; Morris et al. 

2000). A dry, high atmospheric pressure climatic belt 

prevailed in this western part of Pangaea and resulted in 

restricted- marine evaporitic conditions over much of 

southwestern North America (Peterson 1980). 

The sweeping high- angle, cross- stratification in the 

Coconino Sandstone preserves ancient sand dunes that 

were part of a very extensive, Sahara- like aeolian dune 

field, called an erg, which extended from Arizona to 

Montana (fig. 12) (McCormack 1989; Middleton et al. 

2003). The Coconino Sandstone is composed of finegrained, well- sorted, rounded quartz grains and is 

correlative to the Weber Sandstone in Utah and the 

Tensleep Sandstone in Wyoming and Montana. 

Some of the beds of cross- stratification in the Coconino 

Sandstone are up to 20 m (66 ft) thick. Vertebrate and 

invertebrate tracks and trails in the sandstone suggest 

animals traversed the loose dune sand (Middleton et al. 

2003). These sediments and trace fossils record the 

advance and passage of a major aeolian sand sea. 

In northern Arizona the Coconino Sandstone is overlain 

by, or interlayered with, the Permian Toroweap 

Formation. In the Walnut Canyon National Monument 

area, the Toroweap consists of cross- bedded aeolian 

sandstone that is indistinguishable from the Coconino 

Sandstone. The aeolian sandstone of the Coconino 

grades eastward into near- shore marine sandstone beds 

of the Glorieta Sandstone in western New Mexico. To 

the south, the Coconino Sandstone is either interbedded 

with reddish- brown erg- margin sandstones, siltstones, 

gypsum (Schnebly Hill Formation) and tidal- flat 

deposits (Toroweap Formation), or it is sharply overlain 

by the Kaibab Formation. The Toroweap and the Kaibab 

Formation reflect a transgressive episode in which the 

marine environment to the west inundated the Coconino 

sand dune field covering the area with marine sediments. 

The Middle Permian Kaibab Formation is the youngest 

Paleozoic rock unit on the southern Colorado Plateau 

and preserves evidence of an ancient seaway that spread 

over most of northern Arizona about 260 million years 

ago (fig. 13) (Hopkins and Thompson, 2003). At this time, 

the last of the Paleozoic epicontinental seas transgressed 

into northern Arizona. The subtidal, shallow marine 

environments of the Kaibab formed a mixed carbonateclastic ramp (Hopkins and Thompson, 2003). 

Invertebrate fossils in the Kaibab Formation at Walnut 

Canyon National Monument once lived in a regressive 

shallow marine environment (Santucci and Santucci 

1999). The pelecypod Schizodus usually lived in shallow 

hypersaline environments. The fossil assemblage in table 

1 is characteristic of fauna of nearshore brackish 

environments. This regressive shallow marine 

interpretation is supported by the absence of corals in 

the assemblage. Permian corals, like modern corals, 

preferred open, oxygenated marine environments with 

good water circulation. 

The Kaibab Formation on the Coconino Plateau is 

composed of a variety of lithologic types. The 

interbedded carbonate and clastic sediments of the 

Kaibab record a complex depositional history. The 

repetitive and cyclic nature of these deposits documents 

repeated depositional shifts of near- shore and shallow 
 WACA Geologic Resource Evaluation Report 25 

marine depositional environments during pulsed 

transgressions and regressions of the epicontinental sea 

into the region (Hopkins and Thompson 2003). 

The episodic transgressions and regressions were a result 

of the tectonic activity at the margins of the North 

American continent as the global landmasses were 

coming together to form Pangaea. During the Permian 

Period, the western margin of Pangaea continued to 

undergo compression as lithospheric plates collided 

(Silberling and Roberts 1962). The peaks of the 

Uncompahgre Mountains were formed in western 

Colorado from compressional stresses resulting from the 

collision of South American with the southern edge of 

North America. 

The close of the Permian brought the third, and most 

extensive, major mass extinction of geologic time (fig. 13). 

Although not as widely known as the extinction event at 

the end of the Mesozoic Era that exterminated the 

dinosaurs, the Permian extinction event eliminated 

approximately 96% of all species (Raup 1991). 

Triassic Period 

During the Triassic Period (251- 200 Ma), the 

supercontinent Pangaea reached its greatest size. All the 

continents had come together to form a single landmass 

that was centered on the equator (Dubiel, 1994). On the 

western margin, volcanoes erupted from the sea and 

formed a north- south trending arc of islands along the 

border of what is now California and Nevada (fig. 14) 

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

A shallow sea stretched from eastern Utah to eastern 

Nevada over a beveled continental shelf in the Early 

Triassic (fig. 14). The depositional environments in the 

Lower Triassic Moenkopi Formation range from 

offshore marine to continental alluvial fan and include 

fluvial, mudflat, sabkha, and shallow marine sediments 

(Stewart et al. 1972; Dubiel 1994). Fossilized plants and 

animals in the Moenkopi Formation suggest a climate 

shift from the arid, desert conditions at the end of the 

Permian to a warm tropical setting that may have 

experienced monsoonal, wet- dry conditions in this 

region of North America (Stewart et al. 1972; Dubiel 

1994). 

Most of the Moenkopi Formation has been eroded from 

the upper reaches of the Walnut Canyon area. Limited 

exposures of mudstones and thinly bedded sandstones 

preserve shallow marine depositional environments such 

as tidal flats. Lower Triassic strata throughout the 

western U.S. indicate that at least three major 

transgressive- regressive cycles occurred in the Early 

Triassic. The presence of an ammonoid fossil in the 

lower Moenkopi Formation, discovered at Wupatki 

National Monument, indicates that an incursion of a 

shallow sea into this region of northern Arizona took 

place during one of those cycles. (McCormack 1989). 

The Missing Record 

By the end of the Mesozoic Era, Pangaea was broken 

apart into roughly the continents present today. In 

Arizona, about 1.6 km (1 mi) of terrestrial and marine 

rock layers covered the Kaibab Formation (Billingsley 

1989; Morales 2003). Uplift of the southwestern 

Colorado Plateau during the Tertiary, however, initiated 

a major episode of erosion that stripped away the 

Mesozoic rocks from the Walnut Canyon region 

(Lucchitta 2003). Tertiary and Pleistocene rocks and 

sediments also are missing from the region – either never 

deposited, or removed by erosion. In Walnut Canyon 

National Monument, the unconformity between the 

Moenkopi Formation and the first Quaternary deposits 

spans approximately 245 million years. 

During the Mesozoic Era, a volcanic island arc formed 

off the coast of western North America. Subduction 

zones associated with plate collision underlay the 

southern part of Arizona, south of the Walnut Canyon 

region (Pallister et al. 1997). Volcanoes typically form 

over subduction zones as the subducting plate melts 

creating a magma source. 

A tectonic regime change in the Early Cretaceous from 

compression to extension initiated rifting in the 

northwest- southeast trending Bisbee Basin of 

southeastern Arizona (Elder and Kirkland 1994; 

Dickinson and Lawton 2001; Haenggi and Muehlberger 

2005). Rifting tilted the Mogollon slope towards the 

northeast and opened a series of local pull- apart basins 

in southern Arizona (Elder and Kirkland 1994; Anderson 

and Nourse 2005). Streams on the Mogollon flowed to 

the northeast, similar to Walnut Creek. Northeast 

flowing streams emptied into the last epicontinental sea 

that inundated the North American continent (fig. 15). 

This interior seaway extended from the Gulf of Mexico 

to the Arctic Ocean and from Nebraska to central 

Nevada. 

At the close of the Mesozoic, about 65 Ma, another burst 

of volcanic activity and faulting in southeastern Arizona 

resulted from the Laramide Orogeny (about 75- 35 Ma). 

This episode of tectonic compression and mountain 

building formed the modern Rocky Mountains and 

emplaced most of the ores of copper, silver, and gold in 

the southwestern United States (Pallister et al. 1997). The 

Laramide Orogeny caused uplift of the southwestern 

Colorado Plateau and subsequent erosion of most of the 

Mesozoic strata from the Walnut Canyon area. Northflowing, sediment- choked streams dominated the 

landscape and covered parts of northern Arizona with 

100 to 200 m (330 to 660 ft) of gravelly sediments. 

The Laramide Orogeny uplifted the Colorado Plateau, 

reactivated Precambrian faults in a reverse sense, and 

horizontally shortened the western margin of North 

America across north- south trending thrust faults 

(Marshak et al. 2000; Billingsley and Wellmeyer 2002; 

Huntoon 2003). On the Colorado Plateau, east- dipping 

monoclines formed in Paleozoic and Mesozoic strata and 

overlie deep- seated, west- dipping reverse faults. 
26 NPS Geologic Resources Division 

Intervening blocks between monoclines gently warped 

into broad, north- trending arches and basins. 

About 45 Ma (Eocene), plate movement along the west 

coast subduction zone slowed, resulting in a cessation of 

deformation in the Walnut Canyon area (Dickinson 1981; 

Huntoon 2003). Subduction remained active in the 

southwestern United States and volcanism continued in 

southern Arizona during early to middle Tertiary. The 

Santa Catalina Mountains of southern Arizona contain at 

least 12 plutons emplaced in three intrusive episodes: 1) 

60- 75 Ma (Latest Cretaceous to Paleocene), 2) 44- 50 Ma 

(Eocene), and 3) 25- 29 Ma (Oligocene) (Anderson 1988). 

Miocene to Recent 

Subduction off the southwestern coast of North America 

ceased about 20 Ma and the relative motion of the plates 

changed from compressional to transverse, initiating the 

strike- slip San Andreas fault system and extension of the 

crust that would lead to Basin- and- Range normal 

faulting. During the Miocene and Pliocene, the Colorado 

Plateau uplifted as much as 3- 4 km (1.8- 2.5 mi) (Oldow et 

al. 1989). 

The San Francisco volcanic field, north of Walnut 

Canyon National Monument, was the major volcanic 

center on the southwest margin of the Colorado Plateau 

(Luedke and Smith 1991). Locally, the Anderson Mesa 

basalt was extruded during the Pliocene. Volcanic 

activity was almost continuous during the late Cenozoic, 

particularly in the Pliocene and Pleistocene. Volcanic 

eruptions in the San Francisco volcanic field continued 

into the Holocene. The most recent eruptive activity 

took place about 1,000 years ago, forming Sunset Crater, 

Arizona’s youngest volcano (Priest et al. 2001). 

Walnut Creek is a tributary to the Little Colorado River, 

which flows into the Colorado River. The Colorado 

River began incising the Grand Canyon about 5 Ma 

(Spencer et al. 2001; Lucchitta 2003) and its tributaries 

did the same. Radiometric ages of volcanic rocks and 

geomorphic features along the canyon indicate that by 

3.8 Ma, the Colorado River was essentially at its present 

grade in the upper Lake Mead area, and by 1 Ma, it was at 

its present grade in the western Grand Canyon 

(Lucchitta and Jeanne 2001; Hamblin 2003; Lucchitta 

2003). 

The alluvial, colluvial, and lake deposits in Walnut 

Canyon National Monument are the latest chapter in the 

geologic history of the region. Channel downcutting in 

the Holocene left alluvial terrace deposits in the canyons. 

Headward erosion provided additional sediment that 

was transported and deposited to form channel bars, 

point bars, and other alluvial deposits. Lake deposits in 

Walnut Canyon resulted from the impoundment of 

Walnut Creek by the Santa Fe Dam. Mass wasting 

processes work to widen canyons on the Colorado 

Plateau and generate colluvium in the form of talus 

slopes at the base of the cliffs. Visitors to Walnut Canyon 

National Monument are allowed a glimpse into the 

erosion and depositional processes that were ongoing 

throughout geologic history and that continue to shape 

the present landscapes. 
 WACA Geologic Resource Evaluation Report 27 

Figure 11. Geologic time scale; adapted from the U.S. Geological Survey and the International Commission on Stratigraphy. Red lines 

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

North American continent. Absolute ages shown are in millions of years (Ma, or mega-annum). 
28 NPS Geologic Resources Division 

Figure 12. Generalized paleogeographic map showing the approximate distribution of Coconino Sandstone in Arizona during the Permian, 

approximately 170 Ma. Modified from Middleton and others (2003) and Dr. Ron Blakey, Northern Arizona University, Department of Geology, 

http://jan.ucc.nau.edu/~rcb7/perpaleo.html, (Accessed March 2007). 
 WACA Geologic Resource Evaluation Report 29 

Figure 13. Paleogeographic map of northern Arizona during deposition of the Kaibab Formation. Modified from Hopkins and Thompson 

(2003). 
30 NPS Geologic Resources Division 

 WACA 

Figure 14. Paleogeographic map of the Early Triassic during deposition of the Moenkopi Formation. Modified from Dubiel (1994). 
 WACA Geologic Resource Evaluation Report 31 

Figure 15A. Late Cretaceous interior seaway. The sea extended from the Gulf of Mexico to the Arctic Ocean. Modified from Rice and Shurr, 

(1983). 

Figure 156B. Map of streams in the Walnut Canon area flowing into the interior seaway. Map courtesy of Dr. Ron Blakey, Northern Arizona 

University, http://jan.ucc.nau.edu/~rcb7/crepaleo.html, (Accessed March 2007). 
32 NPS Geologic Resources Division 

Glossary 

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

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

here please visit: http://wrgis.wr.usgs.gov/docs/parks/misc/glossarya.html. 

aeolian. Formed, eroded, or deposited by or related to 

the action of the wind. 

alluvial fan. A fan- shaped deposit of sediment that 

accumulates where a high gradient stream flows out of 

a mountain front into an area of lesser gradient such as 

a valley. 

alluvium. Stream- deposited sediment that is generally 

rounded, sorted, and stratified. 

aquifer. Rock or sediment that are sufficiently porous, 

permeable, and saturated to be useful as a source of 

water. 

ash (volcanic). Fine pyroclastic material ejected from a 

volcano. 

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

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

basin (sedimentary). Any depression, from continental 

to local scales, into which sediments are deposited. 

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

completely or in part. 

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

clay. Clay minerals or sedimentary fragments the size of 

clay minerals (<2 cm). 

continental crust. The type of crustal rocks underlying 

the continents and continental shelves; having a 

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

approximately 2.7 grams per cubic centimeter. 

cross-bedding. Uniform to highly- varied sets of inclined 

sedimentary beds deposited by wind or water that 

indicate distinctive flow conditions. 

crust. The outermost compositional shell of Earth, 10- 40 

km (6- 25 mi) thick, consisting predominantly of 

relatively low- density silicate minerals (also see 

oceanic crust and continental crust). 

deformation. A general term for the process of faulting, 

folding, shearing, extension, or compression of rocks 

as a result of various Earth forces. 

dip. The angle between a structural surface and a 

horizontal reference plane measured normal to their 

line of intersection. 

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. 

entrenched meander. An incised meander carved 

downward into the surface of the valley in which the 

meander originally formed. 

epicontinental. Situated on the continental shelf or on 

the continental interior, as an epicontinental sea. 

extrusive. Of or pertaining to the eruption of igneous 

material onto the surface of Earth. 

fault. A subplanar break in rock along which relative 

movement occurs between the two sides. 

formation. Fundamental rock- stratigraphic unit that is 

mappable and lithologically distinct from adjoining 

strata and has definable upper and lower contacts. 

foreset. Pertaining to or forming a steep and advancing 

frontal slope, or the sediments deposited on such a 

slope. 

graben. A down- dropped structural block bounded by 

steeply- dipping, normal faults (also see horst). 

horst. An uplifted structural block bounded by highangle normal faults. 

igneous. Refers to a rock or mineral that originated from 

molten material; one of the three main classes or rocks: 

igneous, metamorphic, and sedimentary. 

intrusion. A body of igneous rock that invades older 

rock. The invading rock may be a plastic solid or 

magma that pushes its way into the older rock. 

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

and parallel to a subduction zone. 

joint. A semi- planar break in rock without relative 

movement of rocks on either side of the fracture 

surface. 

lacustrine. Pertaining to, produced by, or inhabiting a 

lake or lakes. 

lava. Magma that has been extruded out onto Earth’s 

surface, both molten and solidified. 

lineament. Any relatively straight surface feature that can 

be identified via observation, mapping, or remote 

sensing, often representing tectonic features. 

lithology. The description of a rock or rock unit, 

especially the texture, composition, and structure of 

sedimentary rocks. 

lithosphere. The relatively rigid outmost shell of Earth’s 

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

encompasses the crust and uppermost mantle. 

magma. Molten rock generated within Earth that is the 

parent of igneous rocks. 

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

core. 

meanders. Sinuous lateral curves or bends in a stream’s 

channel. 

member. A lithostratigraphic unit with definable contacts 

that subdivides a formation. 

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

that is bounded by steeply- sloping sides or cliffs. 

monocline. A one- limbed flexure in strata, which are 

usually flat- lying except in the flexure itself. 

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

moves down relative to the footwall. 

oceanic crust. Earth’s crust formed at spreading ridges 

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

km (3- 4 mi) thick and generally of basaltic 

composition. 
 WACA Geologic Resource Evaluation Report 33 

orogeny. A mountain- building event, particularly a wellrecognized event in the geological past (e.g. the 

Laramide orogeny). 

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

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

Pangaea. A theoretical, single supercontinent that 

existed during the Permian and Triassic Periods (also 

see Laurasia and Gondwana). 

plateau. A broad, flat- topped topographic high of great 

extent and elevation above the surrounding plains, 

canyons, or valleys (both land and marine landforms). 

pluton. A body of intrusive igneous rock. 

point bar. A sand and gravel ridge deposited in a stream 

channel on the inside of a meander where flow 

velocity slows. 

radiometric age. An age in years determined from 

radioisotopes and their decay products. 

recharge. Infiltration processes that replenish 

groundwater. 

regression. A long- term seaward retreat of the shoreline 

or relative fall of sea level. 

reverse fault. A compressional, high angle (>45o), dipslip fault in which the hanging wall moves up relative 

to the footwall (also see thrust fault). 

ripple marks. The undulating, subparallel, usually smallscale, ridge pattern formed on sediment by the flow of 

wind or water. 

sabkha. A coastal environment in an arid climate where 

evaporation rates are high. 

sandstone. Clastic sedimentary rock of predominantly 

sand- sized grains. 

sediment. An eroded and deposited, unconsolidated 

accumulation of lithic and mineral fragments. 

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- 1/16 

mm). 

siltstone. A variable- lithified sedimentary rock with siltsized grains. 

stratigraphy. The geologic study of the origin, 

occurrence, distribution, classification, correlation, 

age, etc. of rock layers, especially sedimentary rocks. 

strike. The compass direction of the line of intersection 

that an inclined surface makes with a horizontal plane. 

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

relative movement is parallel to the strike of the fault. 

subduction zone. A convergent plate boundary where 

oceanic lithosphere descends beneath a continental or 

oceanic plate and is carried down into the mantle. 

tectonic. Relating to large- scale movement and 

deformation of Earth’s crust. 

terraces (stream). Step- like benches surrounding the 

present floodplain of a stream due to dissection of 

previous flood plain(s), stream bed(s), and/or valley 

floor(s). 

thrust fault. A dip- slip fault with a shallowly dipping 

fault surface (<45o) where the hanging wall moves up 

and over relative to the footwall. 

trace fossils. Sedimentary structures, such as tracks, 

trails, burrows, etc., that preserve evidence of 

organisms’ life activities, rather than the organisms 

themselves. 

transgression. Landward migration of the sea due to a 

relative rise in sea level. 

trend. The direction or azimuth of elongation or a linear 

geological feature. 

unconformity. A surface within sedimentary strata that 

marks a prolonged period of nondeposition or 

erosion. 

vent. An opening at the surface of Earth where volcanic 

materials emerge. 

volcanic. Related to volcanoes; describes igneous rock 

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

water table. The upper surface of the saturated (phreatic) 

zone. 

weathering. The set of physical, chemical, and biological 

processes by which rock is broken down in place. 
34 NPS Geologic Resources Division 

References 

This section provides a listing of references cited in this report. A more complete geologic 

bibliography is available and can be obtained through the NPS Geologic Resources 

Division. 

Anderson, J. Lawford. 1988. Core Complexes of the 

Mojave- Sonoran Desert: Conditions of Plutonism, 

Mylonitization, and Decompression. In Metamorphism 

and Crustal Evolution of the Western United States, 

edited by W.G. Ernst. Englewood Cliffs, N.J.: Prentice 

Hall, 502- 525. 

Anderson, Thomas H., and Jonathan A. Nourse. 2005. 

Pull- apart basins at releasing bends of the sinistral 

Late Jurassic Mojave- Sonora fault system. Boulder: 

Geological Society of America, Special Paper – 393, 97-

122. 

Appel, Cynthia L., and Donald J. Bills. 1980. Map 

showing ground- water conditions in the Canyon 

Diablo Area, Coconino and Navajo Counties, Arizona 

– 1979. U.S. Geological Survey, Water- Resources 

Investigations, Open- File Report 80- 747, scale 

1:250,000. 

Biek, Robert F., Grant C. Willis, Michael D. Hylland, and 

Hellmut H. Doelling. 2000. Geology of Zion National 

Park, Utah. In Geology of Utah’s Parks and Monuments, 

edited by Douglas A. Sprinkel, Thomas C. Chidsey, Jr., 

and Paul B. Anderson. Salt Lake City: Utah Geological 

Association Publication 28, 107- 138. 

Billingsley, George H. 1989. Mesozoic Strata at Lees 

Ferry, Arizona. In Centennial Field Guide, edited by S. 

Beus. Denver: Rocky Mountain Section of the 

Geological Society of America, Vol. 2, 67- 71. 

Billingsley, G.H., and H.M. Hampton. 2000. Geologic 

Map of the Grand Canyon 30’ x 60’ Quadrangle, 

Coconino and Mohave Counties, Northwestern 

Arizona. U.S. Geological Survey Geologic 

Investigations Series I- 2688, scale 1:100,000, 

http://pubs.usgs.gov/imap/i- 2688, (accessed May 

2006), 15 p. 

Billingsley, G.H., and J.L. Wellmeyer. 2002. Geologic 

Map of the Mount Trumball 30’ x 60’ Quadrangle, 

Mohave and Coconino Counties, northwest Arizona: 

USGS Geologic Investigations Series I- 2766, scale 

1:100,000, http://pubs.usgs.gov/imap/i2766, (accessed 

October 2005), 30 p. 

Bills, D.J., M. Truini, M.E. Flynn, H.A. Pierce, R.D. 

Catchings, and M.J. Rymer. 2000. Hydrogeology of the 

regional aquifer near Flagstaff, Arizona, 1994- 97. U.S. 

Geological Survey, Water- Resources Investigations 

Report 00- 4122, 143 p. 

Christiansen, Eric H., Bart J. Kowallis, and Mark D. 

Barton. 1994. Temporal and spatial distribution of 

volcanic ash in Mesozoic sedimentary rocks of the 

Western Interior: an alternative record of Mesozoic 

magmatism. In Mesozoic Systems of the Rocky Mountain 

Region, USA, edited by Mario V. Caputo, James A. 

Peterson, and Karen J. Franczyk. Denver: Rocky 

Mountain Section, SEPM (Society for Sedimentary 

Geology), p. 73- 94. 

Chronic, Halka. 1983. Roadside Geology of Arizona. 

Missoula: Mountain Press Publishing Company, p. 

306- 307. 

Dickinson, William R. 1981. Plate Tectonic Evolution of 

the Southern Cordillera: Tucson: Arizona Geological 

Society Digest, Vol. 14, 113- 135. 

Dickinson, William R., and Timothy F. Lawton. 2001. 

Tectonic setting and sandstone petrofacies of the 

Bisbee Basin (USA- Mexico). Oxford: Journal of South 

American Earth Sciences, Vol. 14, Issue 5, 474- 504. 

Dubiel, Russell F. 1994. Triassic deposystems, 

paleogeography, and paleoclimate of the Western 

Interior In Mesozoic Systems of the Rocky Mountain 

Region, USA, edited by Mario V. Caputo, James A. 

Peterson, and Karen J. Franczyk. Denver: Rocky 

Mountain Section, SEPM (Society for Sedimentary 

Geology), 133- 168. 

Elder, William P., and James I. Kirkland. 1994. 

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 WACA Geologic Resource Evaluation Report 37 

Appendix A: Geologic Map Graphic 

The following page provides a preview or “snapshot” of the geologic map for Walnut 

Canyon National Monument. For a poster size PDF of this map or for digital geologic 

map data, please see the included CD or visit the GRE publications webpage: 

http://www2.nature.nps.gov/geology/inventory/gre_publications.cfm 

 WACA Geologic Resource Evaluation Report 39 

Appendix B: Scoping Summary 

The following excerpts are from the GRE scoping summary for Walnut Canyon 

National Monument. The scoping meeting occurred June 28- 29, 2001; therefore, the 

contact information and Web addresses referred to herein may be outdated. Please 

contact the Geologic Resources Division for current information. 

Summary 

A geologic resources inventory workshop was held for 

the three Flagstaff area NPS units (Walnut Canyon NM, 

Wupatki NM, Sunset Crater NM) on June 28th and 29th, 

2001, to view and discuss the park’s geologic resources, 

to address the status of geologic mapping for compiling 

both paper and digital maps, and to assess resource 

management issues and needs. Cooperators from the 

NPS Geologic Resources Division (GRD), NPS Flagstaff 

area office, Colorado State University, and United States 

Geologic Survey (USGS) were present for the workshop. 

This was part of a multi- park scoping session also 

involving Petrified Forest NP, Pipe Spring NM, and 

Navajo NM. 

On Friday June 29th, scoping involved a half- day field 

trip to view the geology of Sunset Crater NM and 

Wupatki NM, led by Sarah Hanson (Adrian College) and 

Helen Fairley (NPS). On June 28th scoping included 

another half- day session to present overviews of the 

NPS Inventory and Monitoring (I&M) program, the 

Geologic Resources Division, and the on- going Geologic 

Resources Inventory (GRI). Round table discussions 

involving geologic issues for Flagstaff area parks 

included interpretation, natural resources, the status of 

geologic mapping efforts, sources of available data, 

geologic hazards, and action items generated from this 

meeting. 

Currently, the major geologic issues facing the Flagstaff 

area parks are as follows: 

• acquiring digital geologic maps at a large scale suitable 

for resource management needs; 

• production of an interpretive product that could be 

sold in visitor centers showcasing the geologic map of 

each area and its significance to the other resources; 

• evaluating potential volcanic hazards in the Flagstaff 

area and how they might affect park resources, and 

• an inventory of the paleontological resources at each 

park. 

The meeting attendees for the Walnut Canyon National 

Monument session are listed at the end of this appendix. 

Geologic Mapping 

All three Flagstaff area parks are included on the USGS 

publication Map Showing Geology, Structure, and 

Uranium Deposits of the Flagstaff 1 x 2 degree quadrangle, 

Arizona (USGS Map I- 1446, scale 1:250,000). While this 

small scale is not necessarily conducive for resource 

management, it is an excellent compilation map and was 

developed based upon larger scale mapping. However, 

larger scale mapping (at least 1:24,000 scale) is desirable 

for each of the three parks. 

Also, the USGS published the Geologic Map of the Eastern 

San Francisco volcanic field, Arizona (USGS Map I- 953, 

scale of 1:50,000) that also covers the areas of the three 

parks, but the map does not necessarily include geologic 

mapping of each park. Specifically, the only park that is 

fully covered on this sheet is Sunset Crater NM. Walnut 

Canyon NM is completely uncovered and Wupatki NM 

is only partially covered. 

Park staff were interested in seeing a map showing 

travertine deposits because it has numerous implications 

for the cultural significance in population distributions 

and the history of water in the area, so it should be a 

component of any new mapping. 

Additionally, volcanic- and other features should be 

included (vents, flows, lava tubes, ice caves, etc.) as they 

are important in deducing a potential for volcanic 

hazards in the area as well as providing baseline data for 

what types of features exist in the park. 

Digital Geologic Map coverage: It is not known if any of 

the USGS maps (I- 953 and I- 1446) for the area have been 

converted to a digital format. If they have not it is 

suggested that they be scanned, registered and rectified 

for preliminary use in a GIS until new mapping is 

accomplished as they are the best available source of 

baseline geologic data for each park. 

Other Desired GIS Data 

Nicole Tancreto had served as the Flagstaff GIS support 

person, but is now in a GIS position for the Southern 

Colorado Plateau network. She mentioned at the 

meeting that the boundary for Walnut Canyon NM was 

incorrect on our maps, so she supplied GRI staff with the 

correct boundary as ESRI shape files. 

Aerial photography is desired for the entire area and 

would assist in any future needed geologic mapping. It 

was suggested to contact the Vegetation Mapping 

program and the USFS to see if they have such data for 

the area. 

Miscellaneous Items of Interest 

Current natural resource staff at Flagstaff area parks are 

Helen Fairley (archeologist), Paul Whitefield, and Todd 

Metzger. 
40 NPS Geologic Resources Division 

Geothermal development is a hot topic for the Flagstaff 

area, and could have effects on each parks management 

plan. Geothermal development was not noted as an issue 

for Walnut Canyon National Monument. 

Walnut Canyon National Monument 

• General geology of WACA consists of the Kaibab, 

Toroweap, Coconino, Moenkopi formations, as well 

as some igneous cinders. 

• I- 953 does not cover the geology of WACA, and thus a 

large- scale geologic map is definitely needed. 

• Paleontological resources do exist in exposures along 

WACA trails and have been subjected to pilferage over 

the years. A paleontological survey is advised for the 

park. 

• Detailed studies of the alluvial deposits in the canyons 

are desired. Richard Hereford (USGS) is the most 

likely qualified candidate to do this and should be 

consulted for his interest 

• George Billingsley mentioned that there is a dam in the 

park that should be restored and incorporated into the 

parks interpretive story. 

Name Affiliation Phone E- Mail 

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

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

John Graham Colorado State Univ. 970- 225- 6333 rockdoc250@comcast.net 

Sarah Hanson SUCR GIP 520- 526- 0502 

517- 264- 3944 Slhanson@adrian.edu 

Paul Whitefield NPS, Flagstaff area 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. 

Walnut Canyon National Monument 

Geologic Resource Evaluation Report 

Natural Resource Report NPS/NRPC/GRD/NRR—2008/040 

NPS D-38, June 2008 

National Park Service 

Director • Mary A. Bomar 

Natural Resource Stewardship and Science 

Acting Associate Director • Mary Foley, Chief Scientist of the Northeast Region 

Natural Resource Program Center 

The Natural Resource Program Center (NRPC) is the core of the NPS Natural Resource Stewardship and 

Science Directorate. The Center Director is located in Fort Collins, with staff located principally in 

Lakewood and Fort Collins, Colorado and in Washington, D.C. The NRPC has five divisions: Air 

Resources Division, Biological Resource Management Division, Environmental Quality Division, Geologic 

Resources Division, and Water Resources Division. NRPC also includes three offices: The Office of 

Education and Outreach, the Office of Inventory, Monitoring and Evaluation, and the Office of Natural 

Resource Information Systems. In addition, Natural Resource Web Management and Partnership 

Coordination are cross- cutting disciplines under the Center Director. The multidisciplinary staff of NRPC 

is dedicated to resolving park resource management challenges originating in and outside units of the 

national park system. 

Geologic Resources Division 

Chief • Dave Steensen 

Planning Evaluation and Permits Branch Chief • Carol McCoy 

Credits 

Author • John Graham

Review • Lisa Norby and Carol McCoy 

Editing • Trista Thornberry- Ehrlich, Sid Covington, and Melanie Ransmeier 

Digital Map Production • Anne Poole 

Map Layout Design • Andrea Croskrey
Geologic Resources Division 

Natural Resource Program Center 

P.O. Box 25287 

Denver, CO 80225 

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

(303) 969-2090 

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U.S. Department of the Interior