Revised from informal subsurface pay zone within Hermosa Group or Hermosa Formation to uppermost of four substages of Four Corners Stage (new) in Four Corners area of southeast UT, southwest CO, northwest NM, and northeast AZ, within Paradox, San Juan, and Black Mesa basins. The substage of the Four Corners is at base of Honaker Trail Formation of Hermosa Group. Ismay is shale bounded and is nearly time-equivalent across broad areas of Colorado Plateau. Unit is easily recognized by use of mechanical and sample logs, and fusulinids (FUSULINA WEINTZI and FUSULINA HAWORTHI). Diagrammatic cross sections; nomenclature chart. Is youngest Desmoinesian substage defined; younger than Desert Creek Substage (revised) of Four Corners Stage. Pennsylvanian (Desmoinesian) age.

Source: GNU records (USGS DDS-6; Denver GNULEX).

Is uppermost production interval (of 5) in the Paradox Member (Atokan? and Desmoinesian) of the Middle and Upper Pennsylvanian Hermosa Formation (Atokan, Desmoinesian, Missourian, and Virgilian) in the Paradox basin of southeast UT and southwest CO. Overlies Desert Creek production interval. Underlies unnamed uppermost part (evaporite cycle 1) of the Paradox Member. Includes evaporite cycles 3-2 (ascending) and in the lower part of cycle 3 includes the informal "Gothic" black shale unit. "The base and top of the Paradox Member of the Hermosa Formation is usually defined by the first and last halite beds. In the deep part of the Paradox basin, the member consists of 29 identifiable evaporite cycles (Hite, 1960), and its maximum depositional thickness was probably about 7,000 ft (2130.9 m). These cycles are bounded by disconformities and when complete the sequential order from the base upward is (a) anhydrite, (b) very silty fine grained dolomite, (c) silty calcareous black shale, (d) silty fine grained dolostone, (e) anhydrite, and (f) halite with or without potash salts. With the exception of the black shale unit, all of the elements of the cycle were deposited in response to salinity changes in the brine basin. In the deep part of the Paradox basin, the cyclical sequence consists of up to 80 percent halite. Going from basin deep to basin shelf, the amount of halite in the cycles diminishes while the percentage of dolostone and anhydrite increases."

Source: GNU records (USGS DDS-6; Denver GNULEX).