Chiricahua Mountains

Cochise College
Virtual Geology Museum
Arizona Geology
Chiricahua Mountains
Geology Home Page
Geology of Southeastern Arizona

Roger Weller, geology instructor

wellerr@cochise.edu
last edited:  11/17/09


 

 

Chiricahua National Monument


JoAnn Deakin
 

Mississippi State University

and Cochise College

 

Introduction

The Chiricahua National Monument is best known for its interesting and sometimes spectacular volcanic pinnacles' called "fairy chimneys" by many locals.  The monument is located in the southeast corner of Arizona and part of the Coronado National Forest, where it forms an intersection point of four biomes:  the Sonoran Desert, the Sierra Madre Zone, the Chihuahuan Desert and a southern most point of the Rocky Mountain Zone.  The Chiricahua Mountains were formed by high angled normal faulting due to crustal thinning, typical of the Basin and Range province, which extends into Northern Mexico. 

These mountains are surrounded by down dropped valleys (grabens) that form the Sulphur Springs Valley to the west, the San Simon Valley to the northeast and the San Bernardino Volcanic Field to the southeast.  As with many of the mountain ranges in this area, the Chiricahuas are termed "sky islands" (Parent, 1994).  Sky islands are areas of cooler temperatures and increased precipitation due to orographic lifting as compared to the surrounding desert floors.  These mountains serve as oases that include natural springs which feed year-round streams and deeply forested pine, cedar and aspen canyons, and are home to a diverse animal population. 

Paleo Proterozoic Tectonic Setting

           Proterozoic rocks of Arizona are classified into eight separate terranes.  The five northwest terranes comprise the Yavapai supergroup.  The metamorphic rocks in this supergroup are considered the basement rocks or crustal rocks and exhibit dates of 1.6 to 1.8 Ga (Baldridge, 2004).   Prior to their accretion, the southern coast of North America extended as far south as the state of Wyoming.  Geologists believe that during a three million year period from approximately 1.8 to 1.5 Ga, these eight terranes  were accreted to the southwest portion of the continent (Keep 1996).  The first orogenic event that affected this area is known as the Yavapai orogeny, which  generally comprises the first five accretions.  This large encompassing event was followed by the Mazatzal orogeny, dated 1.6Ga to 1.7Ga, which essentially deformed the last three terranes.  Baldridge (2004) states that these rocks are younger towards the southeastern portion of Arizona, and were part of a foreland thrust, or magmatic arc. (See figure 1) Evidence for the Mazatzal Orogeny in southeast Arizona is displayed by the oldest known rock in the area; the Pinal Schist.  Weller (2009) describes the Pinal Schist as a "strongly foliated sericite schist interbedded with quartzose grits of sedimentary origin and a maximum thickness of 6000m.  The Pinal Schist was first described by Ransome (1904) as a "very fine grained metasedimentary rock from the greenschist facies with bimodal suites of volcanic rocks.  To the east of the region, the outcrops are bimodal volcanic, and to the west, the rocks are more of a quartz wacke turbidite."(page 26)   This schist outcrops between the Chiricahua National Monument and the city of Wilcox, Arizona in the Dos Cabeza Mountains (Pallister, du Bray and Hall, 1997).

There are several competing models for the formation of the Pinal Schist.  Bowring and Karlstrom (as cited in Keep, 1996) proposed that it was deformed due to the accretion of a terrane.  This work was published after the work of Conway and Silver (as cited in Keep, 1996) who proposed that deposition occurred along a series of continental margin basins.  Copeland and Condie (as cited in Keep, 1996) posit that the origin of the Pinal Schist was in a continental margin arc/intra arc system.  Anderson (as cited in Keep, 1996) proposed a back arc basin model for its original deposition.  Keep (1996) believes the evidence supports deposition in a rifted basin, which then contracted due to some type of margin inversion.  She uses the evidence of rare outcrops of Pinal equivalents in Sonora, Mexico, as well as gentle folding with no overturned folds, foliation plots and the presence of felsic volcanic magmatics, to support her theory.  Although she does speculate on what could cause this type of basin contraction (sea floor spreading pulses), she presents no evidence for such a mechanism in the region.  In any case, the origin of the paleogeographic setting of these terranes is still a controversial issue (Baldridge, 2004).
 

 

(figure 1) http://jan.ucc.nau.edu/~rcb7/pcpaleo.html
 

Whatever the original depositional setting of the Pinal Schist, by 1.4 Ga the majority of Arizona had been added to the continent, and the area underwent intrusion by felsic magmas.  These Precambrian rocks, which out-crop throughout the southeastern portion of Arizona, can be found in the Huachuca, Whetstone, Rincon, Dos Cabeza Mountains, and east of the Chiricahua National Monument near Hilltop.  Pallister et al.(1997) suggests that these rocks effectively "stitched the terranes to the continent." (page 1)

Paleozoic Sequence

An 800 million year unconformity separates the Proterozoic rocks from the Paleozoic sequence overlying them.  The stratigraphy (figure 2) shows deposition from about 570 until 250 million years ago.  Ransome (1904) first described the stratigraphic sequence of the region; the unfossiliferous Bolsa quartzite lies unconformably on the Pinal schist and is overlain by the Arbrigo formation which contains abundant fossil trilobites, brachiopods and pteropods.  Ransome (1904) submitted samples of these fossils to Dr. Charles Walcott who identified them as Cambrian in age.  The remainder of the Paleozoic sediments are marine in origin, and represent deposition patterns consistent with marine deposition.
 

Mesozoic Sedimentation and Volcanic Activity
 

The geologic column presented by Ransome (figure 2) shows an unconformity between the Paleozoic and Mesozoic Eras that covers approximately 150 million years.  Few rocks from this period are preserved in the record of the Chiricahua Mountains or similar mountain ranges of the region, which likely represents an erosional period due to uplift.  The Mesozoic sediments that are present, are comprised of the rocks of the Bisbee group, and probably represent deposition in a basin from a marine incursion that transgressed from the Gulf of Mexico.   The sediments represent a transgressive cycle as the oldest layer the Glance Conglomerate is overlain by the Morita Formation (mostly shale) which, in turn, is overlain by limestone.  Dickerson and Lawton (2001) describe the Bisbee Basin as the "result of a mid-Jurassic intracontinental rift system." (page 475)    They observe the Bisbee Basin to be the central segment of the rift between the Cordilleran and the Caribbean plates. They also observe the progressive transgression of the sea from the Gulf of Mexico toward the west in the sedimentary record.  Around 160 million years ago, subduction to the west brought about the formation of volcanoes in the Huachuca and Dragoon Mountains, creating calderas as well as faulting (Pallister et al., 1997).  A second round of volcanic activity generally associated with the Larimide orogeny, continued mountain building in the region and the formation of the large copper deposits found in the area.  Morenci to the north and Bisbee to the south west, are two very large open pit copper mines representative of these Mesozoic intrusions.

(figure 2)   http://skywalker.cochise.edu/wellerr/ransome/pg054a.htm

Cenozoic Volcanic Activity

At the beginning of the Cenozoic Era, subduction continued to the west and volcanic activity resumed in southeastern Arizona.  During this time small intrusive plutons of granite were emplaced in the mountains of the Cochise Stronghold to the west as well as the Chiricahuas themselves.  During the Oligocene Era, smaller volcanic eruptions of andesite, basalt and rhyolite occurred, are evident in the National Monument, and underlie the Faraway Ranch Formation.  The Faraway Ranch Formation is composed mainly of rhyolite, dacite and andesite lavas.  Some smaller explosive pyroclastic flows are also found in this formation.  On top of the Faraway Ranch Formation is the Jesse James Canyon Tuff; a welded tuff with thickness in some places of 790 feet.  At this time, the Chiricahuas were uplifted sections of Paleozoic and Mesozoic sediments, with small volcanoes and vents dotting the area. In his 1969 PhD Dissertation, Marjaniemi described this area as being in the intersection of the Sierra Madre Occidental and the Basin and Range tectonic province.  His objective was to identify the source area of the major ash-flow sheets in the area.
 

The Chiricahua Monument itself, at that time, was a valley with slightly higher uplifted areas towards the south.  Around 27 million years ago, a volume of magma intruded under the mountains to the south of the monument.  The magma was silica rich and highly volatile.   Around 26.9 million years, the magma chamber erupted and the Turkey Creek Caldera was born.

The eruption of the magma chamber is estimated to have spewed more than 100 cubic miles of magma into the surroundings.  In comparison, Mount St. Helens, which erupted in 1982, expelled only one-tenth of a cubic mile (Pallister et al., 1997).  The immense amount of material expelled lead to the collapse of the volcano forming the Turkey Creek Caldera.  Much of the expelled mass became clouds of ash and pyroclastic flows that filled the Chiricahua Valley to a depth of 1600 m (Pallister et al., 1997). 
 

A more in-depth look shows that the volcanic flows of this particular eruption are divided into three main layers, all which date to the same time and must have occurred in rapid succession.  The bottom member is composed of a pumaceous ash flow tuff, the middle member is classified as a densely welded pumaceous ash flow tuff, and the upper member is a white ash rich surge bed overlain by a grey medium welded tuff (Pallister et al., 1997).  Overlying the Rhyolite Canyon Tuff is Dacite lava, but the occurrence is rare, being found only on the top of Sugar Loaf Mountain.  Inside the collapsed caldera, lava, flows of ash, pumice and pyroclastic tuffs surround the uplifted central section and the walls of the caldera.  Marjaniemi (1969) described the caldera as exhibiting differential erosion.  The highly resistant silicic rocks of the moat remain, but the dome itself has been removed giving the caldera a cirque like structure. (Geologic Map, figure 3)
 

 

(figure 3) (courtesy of Roger Weller, wellerr@cochise.edu)

 

Interesting Geologic Formations

            The Chiricahua Mountains display the high angle normal faulting associated with crustal thinning over the last 20 million years, which is characteristic of Basin and Range topography.  These mountains exhibit the signature keystone type of block faulting common to many mountain ranges of the region.  Basalt flows are also characteristic of crustal thinning and block faulting. The San Bernardino Volcanic Field, to the southeast, is a basalt flow of Pliocene to Pleistocene age.
 

The interesting volcanic columns in the monument were formed from weathering along joints as the result of cooling of the volcanic flows.  Weathering is accelerated along these joints resulting in the pinnacles in the area.  Volcanic features such as fossil fumaroles, surge beds, solution pans and exfoliation shingles can be seen throughout the park.  Tafoni cavities (Bezy, 2001) are weathered into the rock walls, and create spooned-out features along canyon walls.  Slot Canyons are also common, and attest to the weathering processes that are taking place.
 

Some Views of the Chiricahua Mountains

R.Weller/Cochise College  (Pinnacles in the Park)
 

 

R.Weller/Cochise College (Balancing Rocks)

 

R.Weller/Cochise College. (Cochise Head)

 

Cultural Aspects

Paleo Indians were most likely the first inhabitants of this area.  Ten thousand years ago the climate of the area was cooler and wetter, making the area more hospitable for habitation.  These first inhabitants are believed to have migrated from the north, over the Bearing Strait land bridge.  As the climate changed to dryer conditions over time, these inhabitants evolved into the hunter-gatherers of the desert southwest.  Parent (2006) labeled these people the Cochise culture.  Around 200 B.C., a more agrarian culture labeled the Mogollon evolved, spurred by cultures from southern Mexico.  The Mogollon culture had a more stationary lifestyle evidenced by archeological discoveries which found pottery making, farming and permanent homes (pit houses) as normal  day to day behaviors.  These small settlements were scattered around the Southwest and more are being discovered.  As early as March 2009, a new archeological site for these Mogollon people was unearthed during the construction of a new housing development near the Ft. Huachuca military post in the city of Sierra Vista.  Some authors argue that this culture abandoned their homes around A.D. 1300 (Parent 2006), and may have become part of the Anasazi at a later date.  The  Chiricahua Apaches migrated into the area in the 1500's and moved seasonally from one area to another.  Interestingly the word "Chiricahua" actually translates as "mountains of the turkeys", which makes sense as there are many of them inhabiting the mountain ranges.

          As the Spanish began to explore and settle in the region, conflicts became more frequent between the Apaches and various settlers.  Apaches were a warrior culture who raided not only Spanish settlements, but other Indian tribes as well.  In the middle 1800's, the 10th Cavalry of
 Buffalo Soldiers were stationed in Bonita Canyon which lies in the monument area.  The U.S. Army was racially segregated at the time with the black Buffalo Soldiers commanded by white officers.  Stories abound about the fear the Indians held for these black men, as Indians were unaccustomed to seeing African people.  Eventually the Chiricahua Monument became a protected area under President Calvin Coolidge in 1924, due to the rich history and beauty of the area.

 

 

References

Baldridge, S. (2004). Geology of the American Southwest. Cambridge, Cambridge University Press

Bezy, J.V. (2001). Rocks in the Chiricahua National Monument and the Fort Bowie National Historic Site. Tucson, Arizona Geological Survey

Dickerson, W.R. & Lawton, T.F. (2001) Tectonic setting and sandstone petrofacies of the Bisbee Basin (USA-Mexico). Journal of South American Earth Science, 14, 475 - 504

Keep, M. (1996) Pinal Schist, southeast Arizona, USA: The contraction of a Paleoproterozoic rift basin. Journal of Geological Society. 153(6), 979-993

Marjaniemi, D.K. (1969) Geologic History of an Ash Flow Sequence and Its Source Area in the Basin and Range Province of Southeastern Arizona.  (Doctoral Dissertation, University of Arizona, 1969)

Pallister, J.S., du Bray, E.A., and Hall, D.B., (1997). Interpretive map and guide to the volcanic geology of Chiricahua Monument and vicinity, Cochise County, Arizona, Arizona: USGS Misc. Inv. Ser. I-2541 (1:24,000)

Parent, L. (1994). Chiricahua National Monument. Tucson, Western National Parks Association

Ransome, F.L. (1904). Description of the Bisbee Quadrangle, Arizona. US Geological Survey, Folio 112 17p.

Weller, R. (2009). Virtual Geology Field Trips., Chiricahua Mountains. Retrieved Oct 1, 2009.        http://skywalker.cochise.edu/wellerr/geology_SEAZ/chiricahuas/Chiricahuas-list.htm