Named as a member of Mesaverde formation for exposures on Hatfield anticline, south of Rawlins, Carbon Co, WY, Greater Green River basin. No type locality designated. Is a prominent white, cliff-forming sandstone about 170 ft thick that is part of the Mesaverde formation. Lies above Espy tongue (new) of Steele shale. Lies beneath undivided part of Mesaverde. Is gradational with underlying Espy at Espy Ranch where it grades upward into thick-bedded to massive, light-gray to white sandstone at top. The white cap is usually overlain by a coaly zone in the Mesaverde. Thought to be a littoral sand deposited in a regressive marine environment. Of Late Cretaceous, Campanian age.

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

Revised; assigned as youngest member of Haystack Mountains Formation (new name) of Mesaverde Group (new rank). No type section designated by Hale (1961) so a principal reference section established on west side of Hatfield dome in NE1/4 NE1/4 sec 18, T19N, R88W, Carbon Co, WY, Greater Green River basin. Composed of two gray sandstones. The lower is massive, contains phosphate nodules, and is fossiliferous. The upper bed is fine grained, massive, and iron stained. The two sandstones are separated by dark-gray shale and siltstone. Overlies middle unnamed member and underlies upper unnamed member of Haystack Mountains. Assigned a late Campanian, Late Cretaceous age. Probably originated as marine beach and barrier-bar deposit. Correlation with other units of same Cretaceous age in south-central WY shown on table 1.

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