Text Box: Wyoming Basin Introduction | Physical Features | Resources                                                       The Wyoming Basin is between the Southern and Middle Rocky Mountains provinces, separating the latter two provinces by about 50 miles.  Most of the Wyoming Basin is in Wyoming, but a small portion extends into northwestern Colorado, and an extremely small part–just a few square miles–is in northeastern Utah.  The total area of the province is about 40,000 square miles (the size of Kentucky), with a maximum extent of approximately 250 miles in the north-south as well as east-west directions.  The basin is nearly surrounded by the Rocky Mountains and is bordered by nine separate ranges of the Rockies.  However, it is not hemmed in by mountains along a portion of its northeastern border, at a 50-mile-wide gap between the Laramie Mountains of the Southern Rockies and the Bighorn Mountains of the Middle Rockies; here the Wyoming Basin connects directly with the Great Plains, and the boundary is usually placed along a nearly  straight line of low ridges that are collectively called the Oil Mountain Anticline that extends between the two ranges.  There are also no major mountains along a 50-mile section mostly coinciding with the White River on part of the southern border between the eastern end of the Uinta Mountains of the Middle Rockies and White River Plateau of the Southern Rockies; here the basin connects directly with the Colorado Plateaus.  The Wyoming Basin thus provides a route through the Rocky Mountains that does not go over any mountainous terrain, although the elevation of the province averages about 7,000 feet, nearly all of it lying between 6,500 and 7,500 feet.    General Structure Basins The province is essentially a plateau, but because it is nearly surrounded by mountains it is called a basin or depression; it is also referred to as a sag in the Rockies.  The underlying strata are horizontal or very nearly so over large portions of the province.  Many of these strata, composed mostly of relatively easily eroded shale, siltstone, claystone and sandstone (which in places may be more resistant) were deposited after uplift of the surrounding mountains, but despite the continuing erosion of these mountains, the basin is eroding faster and so the thickness of the strata in the province is decreasing.  Although the name of the province implies that it is composed of a single continuous basin, there are many individual, often very distinctive basins that make up most of the province.  The largest of these is the Green River Basin, also called the Bridger Basin.  It is 170 miles north to south and 140 miles wide, covering most of southwestern Wyoming between the Wind River Mountains on the north and the Uinta Mountains to the south.  This is one of the largest basins in the entire Rockies.  Although large portions of the basin are quite flat, the floor is punctuated with numerous mesas, buttes, high ridges, and local areas of well-developed badlands.  The Green River runs north to south nearly through the middle of the basin.  The large flat area northeast of the Wind River Mountains, in the center of Wyoming, is most commonly called the Wind River Basin, but the area is often divided into two basins:  the Wind River Basin includes the flat land between the Wind River Mountains and the Wind River, and the Shoshone Basin extends from the Wind River to the Owl Creek Mountains of the Middle Rockies.  The entire area is a synclinal trough and much of it has topography typical of badlands.  A particularly developed area of badlands about 45 miles west of the city of Casper is called Hell’s Half Acre, which actually consists of about 320 acres (one source says the main area covers 20 acres) of brightly-colored shale and some sandstone that has been dissected into spires, towers, pinnacles and many oddly-shaped rock features.  The many colors here are partially caused by paleosols (see Badlands National Park in the Great Plains province for a discussion of coloration caused by paleosols).  The region, which is now a local park, served in the past as a trap into which buffalo were herded.  The severe erosion and ruggedness of the park have led to the area sometimes also being called the Baby Grand Canyon and Devil’s Kitchen.  The Laramie Basin is west of the Laramie Mountains; its northern end merges with the southern part of the Carbon Basin (the northern part of which is sometimes referred to as the Hanna Basin).  The Laramie Basin, with dimensions of 90 by 30 miles, is also a syncline, but unlike many of the other basins, has little relief; maximum elevation change is about 500 feet.  One of the largest features here is Big Hollow, 5 miles west of Laramie.  This is a deflation basin, or blowout, produced by wind blowing away shale that has weathered to very small particles.  This blowout is 9 miles long, 3 miles wide, and more than 150 feet deep.  There are other blowouts in the Laramie Basin, nearly all within regions of shale, including Big Basin, which is north of Big Hollow.  Another significant basin lies at the southeastern end of the Wind River Mountains.  It is essentially a syncline between the Rawlins and Rock Springs uplifts.  There are many different terms used for this area, the most common being Great Divide Basin, or simply the Great Divide.  Other names include Red Desert Basin, Red Rim Desert, and Red Desert; some say that the Red Desert covers most of the basin but the term is not a synonym for the basin, while others reserve the term Red Desert for just the southern portion of the basin.  There is an abundance of reddish-gray clay soil in many places.  The area of this unusual basin is about 4,000 square miles, consisting of a floor of very low relief with many patches of alkali, alkali lakes and playas.  Windblown material from the alkali regions has collected into silt dunes, and there are also some sand dunes present.  However, the most significant aspect of the Great Divide Basin is that it is the only area in North America enclosed by the Continental Divide.  This drainage divide, which crosses the province from southeast to northwest, encircles the Great Divide Basin, i.e., the Continental Divide itself divides around the basin, making the Great Divide Basin a region of internal drainage–the largest such region in the province.    Uplifts Although basins dominate most of the area of the Wyoming Basin, and the amount of downfolding in the basins has generally exceeded that of the uplifting that has occurred in the region, there are significant uplifts, some of which are called mountains, and there are many prominent cuestas, escarpments and hogbacks.  Some cuestas are hundreds of feet high; one south of the Great Divide Basin rises 1,000 feet above the basin floor.  Rocks in several of these uplifts are similar in age and type–mostly granitic and metamorphic–to those of the anticlinal mountains in the Southern and Middle Rockies.  Some of the mountains have flanking hogbacks, also similar to many in the provinces to the south and north.  The trend of the majority of these uplifted features is likewise similar to the adjacent mountainous provinces, suggesting to several researchers that the mountains of the Wyoming Basin belong to the Rocky Mountain system, and they have been partially buried by the thick sediments in the basins.  For example, the Oil Mountain Anticline extends in a nearly straight line, although discontinuously, between the Laramie Range of the Southern Rockies and the Bighorn Mountains of the Middle Rockies; Rattlesnake Range, Freezeout Mountain and the Antelope Hills are generally considered to connect the Laramie Range with the Wind River Mountains of the Middle Rockies; and Rawlins Hills near the city of Rawlins, which consist of cuestas and hogbacks produced by erosion of the dome-like Rawlins Uplift, is probably closely related to the Park (Gore) Range to the south in the Southern Rockies.  (The northward extension of the Park Range into south-central Wyoming is often called the Sierra Madre.)  Many of the uplifted areas in the province presently are in the process of exhumation because the rate of erosion throughout the province currently exceeds the rate of deposition.  Other significant elevated areas in the province include Rock Springs Dome (Uplift), 100 miles west of the Rawlins Hills.  This is an elliptical anticline, with hogbacks on its western side and cuestas on the east.  The relatively soft shale in the middle of the structure has been so eroded that a depression, Baxter Basin, has been formed in the center of the dome.  Other domes include Little Dome northeast of the Wind River Mountains, and Circle Ridge Dome near the middle of the state.  Two of the mountainous regions in the province are related to volcanic activity.  The higher of the two is the Elkhead Mountains, at the western foot of the Park Range in northern Colorado.  These are flat-topped sedimentary formations covered by sheets of basalt.  Some of the mesa-like remnants rise 3,000 feet above their surroundings and are among the highest elevations in the province.  The Leucite Hills, about 110 miles northwest of the Elkhead Mountains and north of Rock Springs Dome, are mostly remnants of extinct cinder cones with some lava also present.  They rise about 1,000 feet above the surrounding basin.  This was the first area in the United States where the mineral leucite was found.     Wyoming Basin Introduction | Physical Features | Resources