Image from: http://www.geology.wisc.edu/~carroll/green_river.html |
A 500 foot thick medium to coarse grain sandstone overlays the late Cretaceous Lance Formation. Pollen from this sandstone indicates a Maastrichtian age (~68 mya). The coal rich Fort Union Formation overlays this sandstone. Fossils at the base of the Fort Union Formationa are Puercan NALMA (65 to 64 mya). A thick layer of coarse grained sandstone and conglomerate material is found in the southern San Wash Basin just preceeding the Paleocene/Eocene boundary. (55 mya) The northern Washakie Basin also contains a conglomerate layer slightly earlier in the late Palecoene, representing a tectonic influx of clastic material around 56 mya (Honey & Hettinger, 1989).
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Honey, J. G. & Hettinger, R.D. (1989). Cross section showing correlations of Upper Cretaceous Fox Hills Sandstone and Lance Formation, and lower Tertiary Fort Union and Wasatch formations, southeastern Washakie Basin, Wyoming, and eastern Sand Wash Basin, Colorado
Miscellaneous Investigations Series - U. S. Geological Survey (1989) I-1964
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