The Green River of the Western U.S. rises on the northwest flank of the Wind River Range in west-central Wyoming and flows southward through its broad basin of Tertiary and Cretaceous deposits. Approaching the Utah border, it has sculpted Flaming Gorge, named by Major John Wesley Powell for bright red Triassic rocks that adorn southern portions of the chasm; the scenic gorge now lies within the Flaming Gorge National Recreation Area.
Having initially established its course in Tertiary sediments (from the Green River Lakes, regional volcanism and mountain erosion) the Green River cut through the eastern end of the Uinta Range as it rose from below during the Miocene-Pliocene Uplift. Today, the northern two-thirds of the Gorge is carved in Eocene deposits while the southern third is lined by a progression of Mesozoic, Paleozoic and Precambrian rock (north to south); along its 91 mile course in the Gorge, the Green River (dammed since 1964) has cut through strata representing at least 700 million years of Earth's history.
As we found out today, the Utah portion of the Flaming Gorge NRA is especially scenic, with steep cliffs that rise 1700 feet above the lake; mountainous terrain surrounds the gorge and road signs introduce visitors to the varied rock strata. To the north, in Wyoming, the lake shimmers amidst a vast sage grassland, broken by Tertiary domes, buttes and mesas that illustrate the erosive power of the Green River and its tributaries over the past 30 million years.
