Document Type


Publication Date

Fall 8-10-1954


Sedimentary formations outcropping near Basalt, Colorado, are the Pennsylvanian Minturn formation (approx. 6000 ft.); Pennsylvanian, Permian, and Triassic (?) Maroon formation (6000-8000 ft.); Jurassic Entrada (35-181 ft.) and Morrison formations (326-411 ft.); and Cretaceous Burro Canyon (?) (0-70 ft.), Dakota (108-185 ft.), Benton (approx. 500 ft.), and Niobrara (160 ft. plus), formations. Breaks in sedimentation occur at the tops of the Karoon, Entrada, and Morrison. The Basalt area lies in the center of the Permo-Pennsylvanian trough of west-central Colorado. Accumulation of Minturn evaporites in restricted portions of the trough was followed by withdrawal of the sea and piedmont cyclic deposition of the Maroon red beds. Continental deposition prevailed during Entrada, Morrison, Burro Canyon (?), and part of Dakota time, but the whole region was inundated during Niobrara and Benton time. Conglomerate and sandy shale below the Dakota are probably equivalent to the Lower Cretaceous Burro Canyon formation found to the west, while limestone and shale overlying the Dakota are correlated with the Benton and Niobrara formations of eastern Colorado. Microfossils in the lower Niobrara indicate that the Fort Hays and Smoky Hill faunal zones of Kansas are present in the Basalt area. Early Laramide movement compressed the Permo-Pennsylvanian trough and resulted in northwest trending structures such as the Elk Mountain fault-fold, Castle Creek fault, Capitol Creek syncline, Basalt Mountain syncline, and Red Table Mountain anticline. A later movement resulted in truncation of these structures by the El Jebel and West Basalt Mountain faults. Extrusion of Miocene (?) lavas was followed by minor reactivation of the older faults, which cut the lava in the Basalt area. In Pleistocene time Isolated valley glaciers occupied the northeast and west end of Red Table Mountain.