Revised from informal subsurface pay zone within Hermosa Group or Hermosa Formation to second of four (ascending) 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. This substage is the lower of the three substages of the Four Corners to be assigned to the Paradox Formation of the Hermosa Group. Akah 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 (WEDEKINDELLINA EXCENTRICA and FUSULINA ROCKYMONTANA). Diagrammatic cross sections; nomenclature chart. Older than Desert Creek Substage (revised) of Four Corners Stage; younger than Barker Creek Substage (revised) of Four Corners Stage. Desmoinesian (Pennsylvanian) age.

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

Is third (of 5, ascending) production interval 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 Barker Creek production interval. Underlies Desert Creek production interval. Includes evaporite cycles 9-6 (ascending). "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).