OF-03-18 Geologic Map of the Cascade Quadrangle, El Paso County, Colorado


Describes the geologic setting, mineral resource potential and and geologic hazards of this 7.5-minute quad located immediately west of Colorado Springs. Includes the description of map units, structural geology, geologic hazards, mineral resources and corresponding cross-sections and an oblique view (1:24,000). A 46-page booklet accompanies the map. Digital PDF download. OF-03-18D

From the Author’s Notes:

The Cascade quadrangle covers the southern end of the Rampart Range part of the Front Range uplift. The Rampart Range fault zone forms the range-bounding structure and a tectonic boundary with the Colorado Piedmont to the east. The fault juxtaposes Precambrian rocks on the west against steeply dipping Paleozoic and Mesozoic rocks to the east. The Rampart Range consists mainly of Precambrian crystalline rocks, with Phanerozoic cover rocks limited to its southern end. These rocks lie within the structural and topographic reentrant of the Manitou Springs embayment, where displacement along the Rampart Range fault zone is transferred to the Ute Pass fault zone. The “Great Unconformity” (i.e. the nonconformity between Precambrian crystalline rocks and Phanerozoic sedimentary rocks) is well exposed in deep canyons of the southern Rampart Range, with the sedimentary Cambrian Sawatch Sandstone overlying Proterozoic plutonic igneous and metamorphic rocks. Coarse clastic sediments of Tertiary and Quaternary age are widespread along the mountain front, resting in angular unconformity upon strata of Cretaceous or older age. At higher elevations, dissected remnants of Tertiary gravels cover the gently rolling topography of the Rampart erosion surface that was cut into less resistant granitic bedrock probably during the late Eocene and Miocene. The Colorado Piedmont contains tributaries of the Fountain Creek watershed of the Arkansas River system.