Whether called an embayment, a re-entrant, a basin, a sag, or a geosyncline, the area underlain by the Paradox prism of sedimentary rocks is today no one of these. This prism reveals a complex history of (1) lithologic variation, (2) diverse tilt, and (3) structural deformation. The Paradox facies of the Four Corners region contains important reserves of Pennsylvanian oil. The lithologic variation of any specific sedimentary unit is a function of sedimentational history controlled by provenance and tectonism of the source area, type of transporting agent, chemistry of the marine water, and condition of the sea bottom. The stratigraphic variations involve thickness, intersection of bedding surfaces, diastems, and disconformities, and space available for deposition; all of hich are closely related to the tilt history as well as the positive or negative shifts of the effective wave and current base. These, then, are the controls which affected the juxtaposition of different rock types to yield linear controls on the early regional migration of gas, oil, and water phases. The structural deformation of the Paradox prism, often considered to have occurred at finite points or areas in time such as "Laramide" or "mid-Tertiary," in reality must have occurred almost continuously from the initiation of Paradox basination in early Cherokee time, to the present time. This concept, applicable to most Pennsylvanian basins of rapid subsidence, involves recognition of directions and amounts of regional tilt by mapping finite member thickness, specific lithologic characte , probable successive fluid types, and possible directions of fluid movement throughout post-depositional history of that member. These data are equated within the framework of the inferred compactional history for each stratal member during basinal subsidence. Early gentle folding occurred parallel with the facies strike and the general strike of stratal convergence during the areal crowding of the basin. These earlier gentle structures appeared in areas of relatively greater lithologic competence ("reefs") near the break-in-shelf slope, and provided the major traps for Pennsylvanian oil.

There can be little doubt that later tectonic events not only modified but probably destroyed many oil accumulations as well as masking the locations of the several large Aneth-type fields still to be found in the Four Corners region.

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