South Park (Colorado Basin) - Geology

Geology

Geologically, the valley is a wide faulted syncline sitting between the Front Range to the east and the Sawatch Uplift to the west. The Mosquito Range forms a high barrier along the western side of the valley. The long-extinct Thirty-Nine Mile volcanic field is located just to the southeast. The valley is mostly underlain by Paleozoic and Mesozoic sedimentary rocks concealed by a thin layer of gravel laid down by glaciation during Pleistocene time. The underlying rocks are dipping slightly to the east. The eastern (and newer) side of the valley is underlain primarily by Pierre Shale laid down during Cretaceous time. The western (and older) side of the valley, on the west side of Red Hill, is underlain primarily by Permian and Pennsylvanian rocks. Red Hill runs through the center of the valley as a hogback ridge of tilted Cretaceous and Jurassic sedimentary rocks.