Fountain Formation

The Fountain Formation is a Pennsylvanian bedrock unit consisting primarily of conglomerate, sandstone, or arkose, in the states of Colorado and Wyoming in the United States, along the east side of the Front Range of the Rocky Mountains, and along the west edge of the Denver Basin.

Fountain Formation
Stratigraphic range: Late Pennsylvanian
Red rocks typical of The Fountain Formation seen at Roxborough State Park near Littleton, Colorado
Typesedimentary
UnderliesLyons Formation
OverliesGleneyrie Formation
Thickness0–4,500 feet (0–1,372 m)[1]
Lithology
Primarysandstone, conglomerate
Otherlimestone, shale
Location
RegionDenver Basin
ExtentColorado, Wyoming
Type section
Named forFountain Creek
Named byC. W. Cross, 1894

Origin of name

The Fountain Formation was named by geologist W. C. Cross in 1894 for exposures along Fountain Creek in El Paso County, Colorado.[2]

Stratigraphy
Fountain Formation unconformably overlying Precambrian rocks at the parking lot of Red Rocks Park

The Fountain unconformably overlies Precambrian granite and gneiss. Outcrops of the formation typically dip steeply to the east.

Depositional environment

The formation was formed by the erosion of the Ancestral Rocky Mountains, and deposition by fluvial processes as alluvial fans. The characteristic predominant red color and the composition of the Fountain reflect that of the granites and gneisses from which it was eroded.

Notable outcrops
Outcrop of the Fountain Formation at Garden of the Gods. Scale bar on notebook is 3.9 inches (10 cm)

Fossils

Marine invertebrates have been discovered in a limestone and shale member of the Fountain Formation, cropping out on a low hogback in Perry Park. Invertebrates include bryozoans, brachiopods, crinoids, echinoids, and gastropods.[3]

Plant fossils have been discovered in Garden Park north of Cañon City, including Lepidophloios laricinus, Sigillaria, Syringodendron sp., Lepidophyloides sp., Lepidostrobus sp., Lepidostrobophyllum sp., Calamites, Neuropterus sp., Cyclopteris sp., and Stigmaria ficoides.[4]

Age

Rocks of the Fountain Formation are considered to be of Late Pennsylvanian age, and are between 290 and 340 million years old.

References
  1. Frederickson, E.A., De Lay, M., and Saylor, W.W., 1956, Ralston formation of Canon City embayment, Colorado: American Association of Petroleum Geologists Bulletin, v. 40, no. 9, p. 2120-2148.
  2. Cross, C.W., 1894, Description of the Pikes Peak sheet [Colorado]: U.S. Geological Survey Geologic Atlas of the United States, Pikes Peak folio, no. 7, 5 p.
  3. Ellis, C.H., 1966, Paleontologic age of the Fountain Formation south of Denver, Colorado: The Mountain Geologist, v. 3, no. 4, p. 155-160.
  4. Jennings, J.R., 1980, Fossil plants from the Fountain Formation (Pennsylvanian) of Colorado: Journal of Paleontology, v. 54, no. 1, p. 149-158.

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