Triangulating from the cairns…
Abstract Many structural features affecting the development of the Piceance Creek basin had their inception in Precambrian time when two major shear zones formed across this portion of the Colorado Plateau—the northwest-trending Olympic-Wichita lineament and the northeast-trending Colorado lineament. Some of these structures were rejuvenated in the late Paleozoic Ancestral Rockies orogeny which produced folds as well as normal and reverse faults. Many were again reactivated in the Laramide orogeny. The Piceance Creek basin, covering a small portion of the late Paleozoic Colorado basin or trough, began to form synchronously with the elevation of the Uncompahgre and Uinta Mountain uplifts, following subduction of the Farallon plate, about 63 Ma. Uplifts of other areas around the basin (Axial basin, Gunnison, and White River uplifts) soon followed. Older structures within the basin, such as the White River and Piceance Creek anticlines, were soon buried by Paleocene and Eocene sediments. The basin eventually reached a basement-rock depth of nearly 16,400 ft (5,000 m) below sea level and accommodated some 9,000 ft (2,744 m) of Tertiary sediments that effectively buried all the old in-basin structural features. Epeirogenic uplift and tilting of the entire Colorado Plateau during the Eocene caused an increase in available sediment. Near the end of the Eocene, volcanic activity in the eastern Uinta Mountains supplied a flood of volcaniclastics that overwhelmed the basin. Overriding of the East Pacific rise by the North American plate about 17 Ma (Miocene) caused the entire region to be elevated to its present height, caused extensional faulting and initiated the present cycle of erosion. The most prominent post-Laramide (Neogene) structural features in the basin are low-amplitude folds and numerous fractures, most of which are of Miocene and Pliocene age. Most fold axes do not coincide with those of older folds, but swarms of normal faults are largely confined to axes of both pre-Tertiary and Tertiary anticlines and Tertiary synclines. Well-developed joint sets are mostly of Eocene and Miocene age.
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