4.2.3 Geology

There are three main fault lines in the region:  Oil Creek, Ute Pass, and Rampart Range faults.  The region is rated “zone one” for earthquake potential on a scale of zero to four, with a “four” having the greatest potential for earthquakes.  Very small earthquakes do occur in the region with mostly unnoticeable effects (1).

Fort Carson

Geologic units on Fort Carson range in age from Quaternary (one million years before present to recent) to Pennsylvanian (200-250 million years before present).  Unconsolidated sediments deposited during the Quaternary consist of fluvial and alluvial sands, silts, and gravels, and wind-deposited silts and sands.  Consolidated units include shale, limestone, hard sandstone, siltstone, claystone, and conglomerate sandstone and shale (Dames and Moore 1978).

PCMS

Raton Mesa and Mesa de Maya, both prominent land features in the vicinity of Trinidad, Colorado are capped with basaltic rocks (Armstrong 1972).  The Spanish Peaks are also of volcanic origin.

The geological structure of the PCMS is generally associated with the Apishapa Uplift that trends southeast to northeast across the southern area of the site.  These sedimentary rocks dip generally northeastward 1-3 degrees but may dip up to 36 degrees.  Small faults associated with the uplift are found in the northern edge of the PCMS.  The major smaller structure within the PCMS is the Black Hills Monocline and two associated structures - Sheep Canyon and Muddy Creek monoclines.  Several smaller synclines and anticlines are also associated with these monoclines, including the Model Anticline in the western portion of the PCMS (Nakata Planning Group, LLC 2000).

The geology of Fort Carson/PCMS includes many fossil and crystal formations.  The Installation prohibits removal of fossils and crystals.  The largest set of Jurassic Period dinosaur tracks in North America is immediately adjacent to the PCMS.  They were part of the Installation until that section of property was transferred to the U.S. Forest Service in 1990.  Today, this area is known as the Picket Wire Canyon Lands, which is part of the Comanche National Grasslands.

Regional Setting