Cambro-Ordovician, Ordovician, Mississippian, Pennsylvanian, Permian, Triassic, Jurassic, Cretaceous,

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Tertiary, and Quaternary sedimentary units are present in the Colorado part of the Anadarko basin. All rocks below the Atokan-Desmoinesian series of the Pennsylvanian system appear to have been deposited in broad, shallow epicontinental seas. Strong epeirogenic unwarp of the Sierra Grande-Apishapa uplift beginning in Atokan-Desmoinesian time and persisting with decreasing intensity through Virgil time resulted in the removal from most of this uplifted area of all sediments down to the granite basement. Concurrently, a band of coarse, arkosic, clastic material was contributed to the Atokan-Desmoinesian, Missourian, and Virgilian sediments fringing the uplift areas. Beyond the perimeter of this coarse clastic material Pennsylvanian and lower Permian deposition was normal shallow marine. Definition of the Las Animas arch throughout Permian and Pennsylvanian time was slight, and this feature did not achieve regional prominence until Cretaceous time.

By middle Permian time the Sierra Grande-Apishapa uplift had been completely inundated by Permian seas. Deposition from middle Permian to the close of Permian time was evidently in a restricted basin environment as upper Permian sediments are increasingly evaporitic.

Recent discoveries in the Morrowan series and the Atokan Desmoinesian series on the southern end of the Las Animas arch and in an area from the Freezeout Creek fault zone to the Kansas and Oklahoma state lines give southeastern Colorado increasing stature as an oil and gas province. Lenticular bodies of the Morrowan "McClave" sand and fingers of arkosic sandstone in the Atokan-Desmoinesian on the southern end of the Las Animas arch offer attractive stratigraphic trap prospects of sizeable proportions. Thick lower Morrowan "Keyes" sand intervals and numerous Atokan-Desmoinesian arkosic sands present interesting structural trap possibilities in the area between the Freezeout Creek fault zone and the Oklahoma and Kansas state lines. North and east of the perimeter of arkosic material der ved from the Apishapa-Sierra Grande uplift structural and possibly stratigraphic entrapment of hydrocarbons in carbonate rocks of Missourian, Virgilian, and lower Leonardian age offer a relatively unexplored potential.

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