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This study deals with the stratigraphy and sedimentation of the Permo-Triassic "red beds" and adjacent formations of the McCoy area in west-central Colorado. Except for the lower part, detailed work has not been done previously on this section. Detailed sections are measured and correlated in the field. Specimens are examined microscopically. Regional relationships are presented by means of correlated columnar sections and isometric fence diagrams. The Pennsylvanian or Permian "Schoolhouse sandstone" is a gray, cross-bedded, fine-grained, quartzitic sandstone, probably of beach origin, overlies Pennsylvanian (?) arkoses and siltstones. The Permian (?) State Bridge formation overlies the "Schoolhouse sandstone" or, in some places, Pennsylvanian arkoses. The State Bridge consists of brick-red sandstones, siltstones, and shales, and a central limestone member. Graywacke facies and gypseous facies are present in basal State Bridge. The Upper Triassic basal Shinarump conglomerate unconformably overlies the State Bridge. This formation, which consists of coarse, cross-bedded, quartzitic sandstone and lenticular conglomerate, grades upward into the Chinle formation. The Chinle is composed of deep-red, lenticular sandstones, siltstones, mudstones, and shales, and lenticular intraformational limestone-pebble conglomerate. The overlying and unconformable Upper Jurassic Entrada sandstone is eolian, salmon-pink or buff, cross-bedded, and fine-grained. Above this is the marine Curtis formation, a gray, oolitic, fossiliferous sandstone or sandy limestone. All formations thin northeastward against the Front Range positive element. Permian (?) rocks coarsen northeastward. All rocks show distinct genetic relationships either to the Front Range or Uncompahgre positive element. The "red beds" are of continental origin. State Bridge material probably was derived from the Front Range element, Chinle from the Uncompahgre and Front Range elements
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