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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.
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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.
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Physiographic
regions of Colorado. Map courtesy of
Colorado Geological Survey.
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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.
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Raton
Mesa near Trinidad, Colorado.
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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).
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Capulin volcano.
Photo courtesy of U. S. National Park Service.
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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.
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Goemmer Butte, an igneous intrusion in
foreground, with West Spanish Peak visible through rain shower.
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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.
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Greenhorn
Mountain as observed from I-25 near Colorado City.
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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.
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Teepee
Buttes in Pierre Shale southeast of Colorado Springs. Photo courtesy of Flatirons Mineral Club and
photographer Dennis Gertenbach.
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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.