Alluvium(Phanerozoic | Cenozoic | Quaternary)at surface, covers < 0.1 % of this area
Alluvium: mainly valley fill consisting of silt, sand, and gravel; includes some terrace deposits and glacial drift of Pleistocene age in some areas; locally includes hot spring tufa. The older part of the alluvium, where present, is probably of Pliocene age.
Fort Union formation(Phanerozoic | Cenozoic | Tertiary Cretaceous-Late | Paleocene)at surface, covers < 0.1 % of this area
Fort Union formation: Clay shale, siltstone, and sandstone; local lenses of impure limestone, and numerous lignitic beds; contains Tertiary plant and animal fossils but no dinosaurs; base generally placed at the lowest of the succession of lignite beds within it; includes the Tongue River member, Lebo shale member, and Tullock member.
Wasatch Formation(Phanerozoic | Cenozoic | Tertiary | Eocene)at surface, covers 54 % of this area
WASATCH FORMATION -- in Thrust belt: Main body--Variegated red to gray, brown, and gray mudstone and sandstone; conglomeratic lenses; in southwest Wyoming--Drab to variegated claystone and siltstone, carbonaceous shale and coal, buff sandstone, arkose, and conglomerate. In northwestern part of Green River Basin is thick arkosic light-yellowish-tan sandstone intertonguing with pale-green to gray claystone and shale; in east Wyoming--Drab sandstone and drab to variegated claystone; numerous coal beds in lower part.
Lance Formation(Phanerozoic | Mesozoic | Cretaceous-Late)at surface, covers 0.9 % of this area
LANCE FORMATION north Wyoming--Thick-bedded buff sandstone and drab to green shale; thin conglomerate lenses; south and northeast Wyoming--Brown and gray sandstone and shale; thin coal and carbonaceous shale beds.
Hell Creek formation(Phanerozoic | Mesozoic Cenozoic | Cretaceous-Late Tertiary | Paleocene)at surface, covers < 0.1 % of this area
Hell Creek formation: somber-gray sandstone and greenish shaly clay and mudstone containing dinosaur bones; a few thin lignite and subbituminous coal beds.