Detailed large-scale mapping in the Red Creek area 20 miles south-southwest of Colorado Springs shows two significant geologic features, an angular unconformity at the base of the Pennsylvanian Fountain formation, and a high-angle thrust fault.
The basal beds of the Fountain formation rest across truncated edges of the older Madison, Harding, and Manitou formations. Although the unconformity is exposed in a limited area, it is significant as the first recorded instance of an angular unconformity between the Fountain and earlier Paleozoic formations.
The thrust fault strikes parallel to the mountain front and dips steeply southeast away from the mountains. Overthrusting has been toward the Front Range. To emphasize the thrust direction which is opposite to that on many major thrusts elsewhere along the eastern margin of the Front Range, the Red Creek fault is designated a back thrust.