SEPARATING “GEOMYTHOLOGY” FROM THE REALITY OF THE LATE PALEOZOIC UPLIFTS IN COLORADO, UTAH, WYOMING, NEW MEXICO, AND ADJACENT AREAS

Early workers (e.g. Peale, 1877) believed that mountains in Colorado and adjacent areas had been permanent topographic/structural features since the “Archean.” Lee (1918), in coining the term Ancestral Rocky Mountains, also presumed that Pennsylvanian and modern highlands occupied the same areas, an idea on which the terms Ancestral Front Range and Ancestral Uncompaghre also are predicated. While deeply entrenched in the literature, these terms perpetuate an understanding that is clearly wrong. It is recommended that the terms Arapahoe uplift, Ute uplift and Anasazi uplifts replace Ancestral Front Range, Ancestral Uncompaghre, and Ancestral Rocky Mountains respectively to clearly distinguish Pennsylvanian from Laramide structural features.

New maps resolve conflicts about uplift/basin distribution. Uplifts (Arapahoe, Apishapa, Ute, Sierra Grande, Pedernal, and Zuni/Defiance) are areas with Permian and younger sediments on basement. Areas with preserved pre-Pennsylvanian sediments are in basins. Areas with Pennsylvanian sediments on basement are marginal to uplifts or had pre-Pennsylvanian erosion/non-deposition. Basins include the Paradox, Dalhart, Rowe-Mora, Tucumcari, Orogrande and Central Colorado Trough. The terms Pueblo basin (SE Colorado) and Cuchara basin (S end of Central Colorado Trough) are used rather than Denver basin and Raton basin because the latter features have different geographic extents and did not develop until the Laramide. The Cimarron arch separates the Rowe-Mora basin from the Central Colorado Trough.

Some previously-identified uplifts are platforms (basin areas w/ shoaling water depth to restrict/prevent deposition) or did not exist. Platforms include the Pathfinder in Wyoming, an area in western Wyoming, the Piute/Emery in central Utah, and the Florida and Roosevelt in New Mexico. The Ancestral Sawatch Range did not exist. Mississippian and older sediments preserved on the flanks and on top of the Sawatch Range indicate that the area was within the Central Colorado Trough.

Pennsylvanian isopachs show that the Zuni/Defiance uplift, and Florida and Piute/Emery platforms were arrayed along a structural arch extending from southern New Mexico, across NE Arizona, and into central Utah that forms the W/SW boundary of the Orogrande, Rowe-Mora, and Paradox basins.