Asking the pikas politely…
Precambrian basement 1,700 m.y. and 1,450 m.y. old is overlain by a thin shelf sequence of Cambrian to Mississippian age. This sequence was buried in Pennsylvanian time by thick sequences of clastic sediments shed into the Eagle basin from the Uncompahgre,uplift to the southwest. Both the uplift and the basin continued to be tectonically active, with decreasing vigor, until they were covered by continentd sediments in Late Jurassic time. In the Early Cretaceous, sandstones were deposited in a nearshore environment as a sea invaded the region. A thick sequence of marine shales accumulated during Late Cretaceous time. Near the end of the Cretaceous, deformation, intrusion, and mineralization occurred during the Laramide orogeny. In the Oligocene, large-scale intrusion, accompanied by some mineralization and deformation, was widespread in the region. In the Quaternary, basalt extruded in the Roaring Fork valley; and glacial and post-glacial erosion and deposition contributed to shaping the landscape as we see it today.
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