A NEW MAP OF LATE PALEOZOIC UPLIFTS IN COLORADO, WYOMING, NEW MEXICO, AND ADJACENT AREAS

The location of “Ancestral Rockies” uplifts that developed in the Pennsylvanian is defined by the distribution of sedimentary cover on Precambrian Basement. Areas of major Pennsylvanian uplift are approximated by areas where Permian and younger sediments rest on basement. Areas with preserved Mississippian and older sediments must be in adjacent basins. Areas with Pennsylvanian sediments on basement are marginal to the uplifts and are either areas of pre-Pennsylvanian non-deposition or erosion, or areas where Pennsylvanian uplift was sufficient to erode early Paleozoic rocks before being buried by sediments derived from the adjacent highlands.

The use of the terms Ancestral Rocky Mountains, Ancestral Front Range, and Ancestral Uncompaghre is rooted (Ver Wiebe, 1930) in the incorrect presumption that Laramide and Pennsylvanian uplifts are coincident and represent areas of continuous topographic and structural relief from the Paleozoic to the present. It is suggested that the terms Arapahoe uplift and Ute uplift replace Ancestral Front Range, and Ancestral Uncompaghre respectively. The term Anasazi uplifts is suggested as an alternative to Ancestral Rocky Mountains.

The Arapahoe, Ute, Sierra Grande, Pedernal and Zuni/Defiance uplifts are documented. The Arapahoe Uplift extends NNW from SE of Pueblo diagonally across the modern Front Range, Middle and North Parks, and Park Range and a short distance into Wyoming. Mallory's (1966) Pathfinder uplift in Wyoming is a distal portion of the gentle north flank of the Arapahoe uplift. It includes areas where both early Paleozoic and Pennsylvanian sediments rest on basement and is not a major structural feature. The Ute uplift forms a dog-leg shape in SW Colorado with the Paradox basin to the SW. The oldest sediments to extend continuously across the Arapahoe and Ute uplifts are Jurassic. The Colorado trough lies between the Ute and Arapahoe uplifts and includes the area of the Sawatch range. The Sierra Grande, and Pedernal uplifts are irregular shaped areas in NE and south central New Mexico. The Zuni/Defiance uplift is a roughly circular area with two segments that straddles the New Mexico-Arizona border. Permian sediments rest on basement nearly continuously on the Sierra Grande, Pedernal, and Zuni/Defiance uplifts.