Nature
Wyoming’s Tensleep Sandstone preserves sediments from the Pennsylvanian to very early Permian, more than 250 million years old. Composed mainly of fine- to medium-grained light gray to yellowish-gray sandstone, with calcareous layers and beds of dolomite and sandy dolomite, it is distinguished by thick, massive low-angle wedge-planar crossbeds that record ancient dune environments. In outcrop, it commonly forms cliffs 200 to 300 feet thick, making it a prominent landscape feature. The formation also yielded a fossil trackway reported in 1932 by Edward Branson and Maurice Mehl, who named the ichnospecies Steganoposaurus belli; the footprints were attributed to a web-footed animal likely reptilian rather than amphibian.
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Jeffrey City, Wyoming · United States
