This paleogeographic map reflects the distribution of land and sea during the early part of the Pennsylvanian Period and shows where coarse sediments derived from the Ancestral Rockies were deposited.
FOUNTAIN FORMATION MINTURN FORMATION HERMOSA FORMATION
West of Denver, the main line of the Denver & Rio Grande Railroad tunnels beneath steeply dipping sandstones and [conglomerates] of the Fountain Formation. (Jack Rathbone photo)
Corals, [brachiopods], and [fusulinid] Foraminifurida can be found in the Pennsylvanian Minturn Formation at many places in the Mountain and [Plateau] Provinces.
In western Colorado, where vegetation is sparse, rock structures are clearly defined. This photograph shows beds of the Pennsylvanian Minturn Formation sharply folded, probably as a result of the deformation of gypsum in underlying layers. (Jack Rathbone photo)
In the Flatirons near Boulder, Red Rocks Park near Denver, and the Garden of the Gods near Colorado Springs we see well exposed examples of the Fountain Formation. The Minturn Formation is visible along the Eagle River west of Wolcott, and along Gore Creek near Vail. The Hermosa Formation forms striking red cliffs north of Durango. In the Sangre de Cristo Mountains area, exceptionally great and rapid deposition took place, and the Minturn Formation is very thick.