The Piceance Creek Basin contains a conglomeratic / coarse grained sandstone unit (Ohio Creek Conglomerate) recently dated by pollen as late Palecene, indicating that clastic sedimentation did not begin until around 57 mya (Patterson et al, 2003). The White River Uplift on the western flank of the Rocky Mountains deformed middle to late middle Eocene sediments, and may have erased an older and more proximal record of conglomeratic sediments. Sedimentation continued in the basin until about 45 mya (late middle Eocene).