Great Divide Basin
Some precipitation falling along the Continental Divide never flows out of Wyoming, leaving the state only by evaporation. A hydrologic basin containing shallow lakes that have no outlet exists on top of the continent in Wyoming. Covering approximately 3,900 square miles, this area is called the Great Divide Basin. The Continental Divide follows the crest of the Wind River Range and splits near South Pass, with one part trending south-southeast and the other east. It becomes a single divide again at historic Bridger Pass south of Atlantic Peak, approximately 20 miles southwest of Rawlins, and then continues southeast on the crest of the Sierra Madre. This split in the Continental Divide encloses an area of interior drainage characterized by ephemeral streams, permanent and playa lakes, and scrub vegetation used largely for winter pasture.
Travelers on Interstate 80 between Rawlins and Rock Springs may not realize it, but they will have crossed the Continental Divide twice and driven through the southern part of the Great Divide Basin. The first crossing is approximately 5.5 miles west of Rawlins near the Hadsell exit; the second crossing is between the Red Desert and Table Rock exits, approximately 58 miles west of Rawlins. Because of the red- and purple-colored rocks and soil in the area, this basin is often called the Red Desert.
Geologically, the Great Divide Basin is one of the two eastern sub-basins within the Greater Green River Basin. It is separated from the Washakie Basin to the south by the east-west-trending Wamsutter arch; bounded on the east by the Rawlins uplift; bounded on the north by the Granite Mountains (and related Crooks Mountain-Green Mountain uplifts) and the southern Wind River Range; and on the west by the north plunge of the Rock Springs uplift. The deepest part of the basin lies along the steep east flank of the Rawlins uplift and the northern mountains. The Great Divide Basin contains a thick sequence of marine Upper Cretaceous and continental early Tertiary rocks as well as lacustrine rocks related to the Eocene Green River Formation. A thick, early Eocene arkosic conglomerate called the Battle Spring Formation crops out in the northeast third of the basin and interfingers with finer-grained rocks in the rest of the basin. This conglomerate was derived from the Granite Mountains that once stood high above the northern part of the basin.
Because of its location at the top of the continent, and the fact that no high mountain masses exist to the west or the east, the Great Divide Basin presents no restriction to the westerly airflow pattern of western North America. This westerly flow is “funneled” through southwestern Wyoming between the mountain masses of the Overthrust Belt/Wind River Range in Wyoming and the Wasatch/Uinta mountains in Utah. In other words, the wind blows, and it blows a lot, in this part of Wyoming. Because southwestern Wyoming is a desert environment and many of the outcropping rocks are poorly consolidated and easily eroded, it is no coincidence that the Great Divide Basin is home to extensive sand dune fields. For example, the Killpecker dune field, which extends some 90 miles across the Great Divide Basin from near Farson to 20 miles north of the town of Wamsutter, is the largest continuous area of active sand dunes in the U.S. Surrounding the areas of active sand dunes are even larger areas of stabilized or inactive dunes.