COLORADO GEOLOGY: I-25 CORRIDOR SOUTH

Looking south down the Canadian Escarpment near summit of Raton Pass, I -25 with vehicles on right.  Volcanic structures in far distance are in New Mexico: Canadian River Physiographic Section.

Many visitors to my home town of Colorado Springs arrive from the south via Interstate 25.  This route produces sights of some spectacular geological features beginning with the climb up Raton Pass (7834 feet and the passageway for the Santa Fe Trail) from New Mexico and entering into the Raton Physiographic Province (RPP).  The Province lies east of the front range (Sangre de Cristo Mountains) in the southern part of the Colorado, but extends into northern New Mexico, hence the name “Raton.”  The southern boundary is the impressive Canadian Escarpment leading down to the drainages of the Canadian River in northern New Mexico.  The indistinct eastern and northern boundaries are usually established at the limits of the extrusive or intrusive volcanic outcrops. 

 

Physiographic regions of Colorado.  Map courtesy of Colorado Geological Survey.

The RPP has a spectacular array of mesas capped with volcanic flows, and dikes, sills, and various other igneous intrusions (there is much to explore here).  The bedrock is often of Late Cretaceous age although some Tertiary sedimentary rocks are present.  In fact, the Cretaceous-Tertiary boundary (K-T), with a clay layer containing high concentrations of iridium,  may be located and seen at Trinidad Lake State Park in Colorado and again across the border at Sugarlite State Park in New Mexico.  These K-T rocks often contain thick coal beds and at one time Trinidad and Walsenburg, Colorado, and Raton, New Mexico, were major coal mining centers.  The western part of the RPP is also a structural basin with beds dipping toward the center (a large syncline) but still is a topographic high!  This has, at times, lead to confusion in names between the structural basin (Raton Basin) and the physiographic province (Raton Province).  The Colorado Geological Survey uses the term Raton Basin for both features.  

 

Raton Mesa near Trinidad, Colorado.

One of the best known structures in the RPP is Raton Mesa near Trinidad and continuing eastward along the Colorado-New Mexico state line where thick (~800 feet) late Tertiary basalt flows (~3.5--9.0 Ma) cap the Poison Canyon Formation (Tertiary: Paleocene) and hold up the topography.  The area, including Barella Mesa and Johnson Mesa, is often referred to as the Raton-Clayton Volcanic Field since the basalt extends as far east as Clayton, New Mexico.  The Raton Mesa, including Fishers Peak (9626 feet), is the highest point in the United States east of I-25; therefore, it is also the highest point east of the Rocky Mountains, surpassing Harney Peak in the Black Hills!  

Many travelers bound for Colorado Springs often take a short eastern detour immediately south of the Colorado-New Mexico state line and visit Capulin Peak or Capulin Mountain, a cinder cone volcano (~8,182 feet) with associated lava flows.  The latest eruption was only about 62k years ago (U. S. National Park Service, 2005).

 

Capulin volcano.  Photo courtesy of U. S. National Park Service.

Further east on the plains, “near” Tobe, and Walt’s Corner, Colorado,  is an isolated mesa termed Mesa de Maya where 400-500 feet of basalt cover the Ogallala Formation at an elevation of around 6500 feet.  The Mesa continues south and eastward as Black Mesa and actually extends into the Oklahoma Panhandle where at 4973 feet it is the highest point in Oklahoma. Smaller, but associated mesas, include Fowler and Tecolete. The Tertiary rocks (Ogallala) at Mesa de Maya have produced an important fauna of vertebrate animals.

The north end of the RPP is bounded by a broad structural uplift, an anticline, termed the Apishipa Uplift.  To the north of this uplift is the structural downwarping (syncline) termed the Denver Basin.  These large structural features are related to the forces that created the front ranges to the west (Laramide Orogeny). The Denver Basin is a subsurface occurrence while the surface topography is part of the Colorado Piedmont and the High Plains Physiographic Provinces. 

The Purgatorie River has cut through the Apishapa Uplift and created  magnificent canyons.  For a great siide trip travelers may want to visit Vogel Canyon and Picture Canyon, sites of prehistoric Native American rock art and village sites, and Picketwire Canyon (supervised by the U. S. Forest Service) with the largest known accumulation of dinosaur tracks in the U.S.  Both are near La Junta, Colorado. 

Perhaps the most spectacular part of the RPP is the Spanish Peaks, two large igneous bodies that have intruded the sedimentary rock section. The igneous rocks exposed at the peaks, and their accompanying dikes, were intruded in the neighborhood of 20-25 Ma (Penn, 1995).  East and West Spanish Peaks reach elevations of 12,708 feet and 13,623 feet respectively, rising about 7000 feet above the surrounding plains. They are impressive structures as observed from the I-25 and are easily seen from Colorado Springs on a clear day!  Also see Blog posting Huerfano Peak on Dec. 7, 2013.

 

Goemmer Butte, an igneous intrusion in foreground, with West Spanish Peak visible through rain shower. 

The emplacement of the Spanish Peaks, Huerfano Peak, Gardner Butte,  Goemmer Butte, the Black Hills, Bandito Cone, and the Spanish Peaks Dike System—may be related to the opening of the Rio Grande Rift System on the west side of the Sangre de Cristo Range.

After leaving the Spanish Peaks-Huerfano Butte area a majestic, but relatively unknown, peak, begins to dominate the mountain skyline to the north and west--Greenhorn Mountain (12,347 feet).  The peak represents the southern end of the Wet Mountains, a somewhat “forgotten range” without a national park, historic ghost towns and major mining areas, major dissecting roads, resorts, a 14er, or even a 13er!  What is does have is beautiful scenery, and some interesting and quite complex geology. 

 

Greenhorn Mountain as observed from I-25 near Colorado City.

The Wet Mountains, essentially the southernmost part of the Colorado Front Range, occupy the site of a former late Paleozoic uplift, the Apishapa Uplift, part of the Ancestral Rocky Mountains.  The range has a Precambrian core with a variety of exposed rocks, including intrusive granitic plutons with dates focusing at 1.4 and 1.7 Ga.  Greenhorn Mountain itself is capped with volcanic (andesite) flows dated as Oligocene, ~33.5 Ma (MacIntosh and Chapin, 2002).  A large thrust fault dominates the eastern front while normal faults produce a graben, the Wet Mountains Valley, on the west.  A sedimentary section is well-exposed around the range, especially in the Canon City area.

Perhaps the “most famous” item about the Wet Mountains is that thousands of geology students have received their initial “professional” experience, in the form of summer field camp, in the range and surrounding areas.  Fort Hays State University, my first teaching institution, offered a camp headquartered at Beulah for many years. In addition, Wichita State University and Kansas State University called Beulah home.  The University of Kansas has a permanent teaching facility north of Canon City and has offered classes since 1922.  Oklahoma State University (since 1949), the University of Oklahoma (since 1950), and the University of Georgia also have facilities in the area, and numerous other institutions make shorter stops to study the rocks.  It truly is the training ground for geologists.

Between Pueblo and Colorado Springs, especially east of Exit 122 at the Colorado Speedway, are a series of topographic cones termed “Teepee Buttes.” These interesting features may approach 30 feet in height and have a central carbonate core that seemed to “grow’ in the Cretaceous Pierre Shale; actually they are associated with methane seeps. The limestone centers of these carbonate mounds have produced a fauna dominated by the bivalve Nyphalucina.  Howe and Kauffman (1985) and Kauffman and others (1996) believed that the cones were associated with Laramide (Rocky Mountain uplift) faulting that allowed spring waters and the methane to reach the surface and “feed” the unique ecological system.  Today these features are being studied as fossil analogs to modern methane seeps.

 

Teepee Buttes in Pierre Shale southeast of Colorado Springs.  Photo courtesy of Flatirons Mineral Club and photographer Dennis Gertenbach.

For a great description of Teepee Buttes I refer readers to a GSA field guide article by Shapiro and Fricke (2002) at http://fieldguides.gsapubs.org/content/3/94.full

By this time the RMFMS travelers are approaching the southern end of Colorado Springs, a city whose landscape is dominated by Cheyenne Mountain (home of NORAD), Pikes Peak (14,115 feet), with the Rampart Range trending north.  The Great Plains continue east to Kansas and beyond.  

REFERENCES CITED

Howe, B., and Kauffman, E.G., 1985, The Lithofacies, Biofacies and Depositional Setting of Tepee Buttes, Cretaceous Submarine Springs Between Colorado Springs and Boone, Colorado, in Kauffman, E.G., ed., Cretaceous Biofacies of the Central Part of the Western Interior Seaway, A Field Guidebook: 4th North American Paleontological Convention, University of Colorado, Boulder.

Kauffman, E. G., Arthur, M. A., Howe, B., and Scholle, P. A., 1996,Widespread Venting of Methane-rich Fluids in Late Cretaceous (Campanian) Submarine Springs (Tepee Buttes), Western Interior Seaway, U.S.A.: Geology, v. 24, n. 9.

McIntosh, W.C., and Chapin, C.E., 2002, Geochronology of the Central Colorado Volcanic Field, in Cather, S.M., McIntosh, W., and Kelley, S.A., eds., Tectonics, Geochronology and Volcanism in the Southern Rocky Mountains and Rio Grande Rift: New Mexico Bureau of Mines and Mineral Resources Bulletin 160.

Penn, B. S., 1995, What’s the Scoop on Huerfano Butte? [abs.]:  American Geophysical Union Abstracts with Program.

U. S. National Park Service, 2005, Geology Field Notes, Capulin Volcano National Monument: http://www.nature.nps.gov/geology/parks/cavo/index.cfm