Local relief in the mountains of southern and central Wyoming at the end of the Eocene was as great as if not greater than it is today. This is indicated by large valleys containing the lower Oligocene White River Formation that extend into the Precambrian cores of the Medicine Bow and Laramie mountains. There has been little deformation of White River rocks in the valleys or on the margins of the mountain ranges, precluding post-Eocene block uplift as a source of modern topographic relief. The regionally widespread low-relief subsummit surface was developed during the Miocene, and is not part of the late Eocene unconformity. Other Oligocene valley fils in the Rocky Mountains indicate that high local relief was widespread during the late Eocene.