Description
Extending previous CGS mapping efforts on the Western Slope of Colorado, this publication describes the geology of this 7.5-minute quadrangle located nine miles east of the Colorado-Utah border with the Colorado River cutting through the quadrangle from east to west. Includes GIS data and two PDF plates. Digital ZIP download. OF-15-14D
From the Geologic History section on Plate 2:
The Mack 7.5-minute quadrangle is in far western Colorado, nine miles from the Utah border. The Colorado River and Interstate 70 cross the quadrangle at the geomorphic transition from the Grand Valley homocline to structural terrain of the Uncompahgre Plateau. North of Interstate 70, the quadrangle lies on flat lands underlain by the thick Mancos Shale, much of which is irrigated with Colorado River water through the Grand Valley irrigation canal system. Pleistocene-aged alluvial fans and stream gravel that flowed from the Book Cliffs have formed small mesas and adobe badlands in the valley through base-level erosional lowering and topographic inversion. South of Interstate 70 the quadrangle enters folded and uplifted terrain of the Uncompahgre Plateau in the public canyonlands of the U.S. Bureau of Land Management’s McInnis Canyons National Conservation Area (MCNCA). Immediately southeast of the quad is the Colorado National Monument, which contains similar topography, geology, and the same general NW-SE trends of the regional structural geologic terrain.
