Unique Geology

Corral Bluffs features cliffs which drop 400 feet to the valley floor. The rim offers scenic views of Pikes Peak and the Front Range, the Sangre de Cristos, Wet Mountains and the eastern plains. The cliffs themselves display layers of different colored stone and sand. Some of the layers have been sculpted by erosion into hobgoblin “hoodoo” shapes. Corral Bluffs is also the headwaters to Jimmy Camp Creek. But here on the high plains, the several dry beds turn into running streams only when there's enough rain. The exposed layers of sedimentary rock offer clues to a starkly different, wetter environment:  a lost world of rivers and forests that dropped hints of its passing in mud banks and gravel bars some 60 million years ago. 

The geologic story of Corral Bluffs is part of the larger story of the forming and filling of the Denver Basin. Corral Bluffs and the contiguous Jimmy Camp Creek canyon area are located on the southern rim of the Denver Basin and together they contain the basin’s largest exposed sequence of Late Cretaceous and Early Tertiary rocks. 

The Denver Basin was created when the so-called Laramide Front Range was formed about 70 to 40 million years ago. As the mountains pushed up, a huge basin formed next to them. Over millions of years, this basin filled with layer after layer of gravel, sand and mud, eroding from the adjacent new mountains. Strata several thousand feet thick in the Denver Basin document this erosion of the Laramide Rockies.

S.B. Roberts, S.B., 2004, Coal in the Front Range Urban Corridor--An Overview of Coal Geology, Coal Production, and Coal-bed Methane Potential in Selected Areas of the Denver Basin, Colorado, and the Potential Effects of Historical Coal Mining on Development and Land-use Planning, Chapter F (p. 117-162) in Fishman, N.S., ed., Energy Resource Studies, Northern Front Range, Colorado, U.S. Geological Survey Professional Paper PP-1698. Figure 11. West-east cross section A–A’ showing the distribution of synorogenic deposits in the unconformity-bounded D1 and D2 sequences, Denver Basin, Colorado. Location of cross section is shown in figure 1. Modified from Raynolds (1997).” Raynolds, R.G., 1997, Synorogenic and post-orogenic strata in the central Front Range, Colorado, in Bolyard, D.W., and Sonnenberg, S.A., eds., Geologic history of the Colorado Front Range: Rocky Mountain Association of Geologists, 1997 American Association of Petroleum Geologists— Rocky Mountain Section Field Trip No. 7, p. 43–47.

 The Denver Museum of Nature and Science (DMNS) has conducted several recent studies as part of their Denver Basin Project. 

Part of the effort by DMNS in 1999 was drilling a core of rock 2.5 inches in diameter and 2,256 feet deep in Kiowa, Colorado. Study of this rock core is ongoing, but they were able to create a map of the Denver Basin and model the numerical ages of the rock layers filling the basin.  (See map below.)

The Denver Basin - Raynolds RG, Johnson KR, Ellis B, Dechesne M, Miller IM (2007) Earth history along colorado's Front range: Salvaging geologic data in the suburbs and sharing it with the citizens. GSA Today: Vol. 17, No. 12 pp. 4–10

Close up of Jimmy Camp/Corral Bluffs area. The red line is the K-T Boundary.

 Layers of rock that can be distinguished from other layers and shown separately on geologic maps are called formations.  Formations are usually named for locations where the rocks were first described and/or are particularly well exposed.  Geologists have used different formation names, notably the Denver Formation and the Dawson Arkose, for the rock layers at Corral Bluffs.  Raynolds (1997) proposed a terminology useful for basin-wide application that overcomes the difficulties that sometimes put previous formation names in conflict.  In the Raynolds scheme, Corral Bluffs is part of the D1 Sequence. (See illustration below.)

From Roberts 2004 “Figure 2. Generalized Upper Cretaceous and Tertiary stratigraphy for different areas in the Denver Basin, Colorado. Modified from Kirkham and Ladwig (1979, 1980) and Nichols (1999). D1 and D2 sequences represent Laramide synorogenic deposits as defined by Raynolds (1997). Diagram not to scale.”

Corral Bluffs lies between the K/T Boundary at Jimmy Camp and the “fossil soil” (paleosol) layer of red and orange colors seen at the Paint Mines in Calhan.  In relative time, Corral Bluffs layers were created after Jimmy Camp Creek layers but before the Paint Mines layers.  In numerical or “sidereal” years, the Corral Bluffs rock layers were deposited between 65.5 and 64 million years ago. 

The K-T Boundary is a very important horizon that marks the extinction of the dinosaurs and the blossoming of our current day animals and vegetation. An exposure of the K-T boundary at West Bijou Creek, on the eastern side of the Denver Basin, is a distinctive 2-cm-thick claystone layer within a 90-cm lignite bed (Raynolds, et al, 2007). See our Paleontology page for more explanation of its importance.  

K-T stands for Cretaceous-Tertiary.  "K" is the traditional German abbreviation for the Cretaceous Period.  Layers such as this give geologists and paleontologists a marker by which to date the rocks and fossils above and below it.

Coal is also found at Corral Bluffs.  From 1882-1965 coal was mined just south of Corral Bluffs at the Franceville Coal Mine.  See our History page for more details on the Franceville Coal Mine. 

 A local geologist, Ken Weissenburger, has volunteered his time to help map, correlate and document the layers at Corral Bluffs and to help us with educational activities.  Please check back for new information.