The Tongue River is a tributary of the Yellowstone River, approximately 265 mi (426 km) long, in the U.S. states of Wyoming and Montana. The Tongue rises in Wyoming in the Big Horn Mountains, flows generally northeast through northern Wyoming and southeastern Montana, and empties into the Yellowstone River at Miles City, Montana. Most of the course of the river is through the beautiful and varied landscapes of eastern Montana, including the Tongue River Canyon, the Tongue River breaks, the pine hills of southern Montana, and the buttes and grasslands that were formerly the home of vast migratory herds of American bison.
The Tongue River watershed encompasses parts of the Cheyenne and Crow Reservations in Montana. The headwaters lie on the Bighorn National Forest in Wyoming, and the watershed encompasses the Ashland Ranger District of the Custer National Forest. The river's name corresponds to Cheyenne /vetanoveo'he/, where /vetanove/ means "tongue" and /o'he'e/ means "river".
Geography
The Tongue River is fed by winter snowpack from the higher elevations of the Big Horn Mountains, early snow runoff of the lower elevations in the drainage basin, and ground water from springs in the drainage basin. The river level rises in March and April due to snowmelt in the lower elevations, and again in June as summer weather melts the higher-elevation snowpack. The flow of water in the upper river during the summer is generally steady, but in the later months of a dry summer, irrigation can reduce the lower river to a few pools of water connected by a small trickle. The river is generally frozen during the winter months.
The source of the Tongue River is in the highlands of the Big Horn Mountains in north-central Wyoming. The river descends the eastern side of the mountains and emerges from a canyon near Dayton, Wyoming. The river then flows eastward, past Ranchester, Wyoming, and merges with Goose Creek, after which the Tongue turns to flow northeast into Montana, where it is dammed, forming the Tongue River Reservoir. Continuing northeast from the reservoir, the river flows through a prairie canyon and the Tongue River breaks, passing Birney, Montana.
The river forms the eastern boundary of the Northern Cheyenne Indian Reservation from about north of the reservoir to a point north of Ashland, Montana, after which the river continues to flow in a broad valley to its mouth on the Yellowstone River near Miles City, Montana. The Tongue River Valley near Decker, Montana also contains the southeast corner of the large Crow Indian Reservation.
The Tongue River headwaters are on the Bighorn National Forest. On forested buttes lying between the Tongue River and Pumpkin Creek is the Ashland Ranger District of the Custer National Forest, which has three separate ranger districts, the other two being the Beartooth Ranger District located in the area of the Beartooth uplift, and the Sioux Ranger District located in the southeast corner of Montana and the northwest corner of South Dakota.
The term "Tongue River Canyon" can refer to either the river's mountain canyon in the Big Horn Mountains of Wyoming, or the river's prairie canyon in Montana, located downstream from the Tongue River Dam and Reservoir.
The major tributaries of the Tongue are Pumpkin Creek, Otter Creek, Hanging Woman Creek, Prairie Dog Creek and Goose Creek. All of these tributaries enter on the eastern side of the river, and all flow in a northerly direction.
Pumpkin Creek meets the Tongue about above the mouth of the river, and extends for into the Custer National Forest; the small community of Sonnette, Montana is at the headwaters. Otter Creek enters the Tongue River near Ashland, Montana, about upstream of the mouth of the river, and its headwaters are near the Wyoming–Montana state line about to the south. Hanging Woman Creek empties into the Tongue at Birney, Montana, about above the mouth of the Tongue, and its headwaters are away in northern Wyoming. Prairie Dog Creek and Goose Creek flow into the Tongue at the point where the Tongue turns from an eastward direction to flow toward the northeast. Goose Creek drains a scenic, well-watered basin in Wyoming, on the eastern edge of the Big Horn Mountains, where Sheridan and Big Horn, Wyoming are located.
The drainage basin to the west is the Rosebud Creek basin. The drainage basin to the east is the Powder River basin. Both rivers, like the Tongue, flow in a northerly direction into the Yellowstone River.
The Tongue and its tributaries flow through parts of Custer, Powder River, Rosebud and Big Horn counties in Montana, and Sheridan County in Wyoming.
Climate According to the Köppen climate classification system, the Tongue River has a semi-arid climate, abbreviated "BSk" on climate maps.
Geology The Tongue River basin is part of the larger geologic structure known as the Powder River basin. The term Powder River basin can refer to the topographic drainage basin lying to the east of the Tongue River drainage basin, but the term is used in this part to denote the larger geological structure which stretches from the Black Hills to the Big Horn Mountains and which includes the Tongue River drainage area.
The Powder River basin is shaped like a large shallow bowl, with its westernmost rock formations lying against the Big Horn Mountains. As these mountains uplifted over eons of geologic time they lifted and tilted the sedimentary rocks from the Powder River basin, which were then eroded away, creating the plains that stretch eastward from the mountains into the basin. Generally there are older sedimentary layers closer to the mountains and younger layers farther away.
As the Tongue flows out from the Big Horn Mountains it passes over the uplifted layers of increasingly younger sedimentary rocks. In the Big Horn Mountains the Tongue flows in its mountain canyon of Madison Limestone, which was deposited during Early to Middle Mississippian time, about 359 to 326 million years ago. As the Tongue leaves the mountains it flows through younger formations, including the distinctive thick red Chugwater Formation, deposited during the Triassic time, 250 to 199 million years ago. Shortly after leaving the mountains, the Tongue River enters an area dominated by a thick layer of buff-colored sandstones and silty clay. This sedimentary layer is named the Tongue River Sandstone, because its outcrops are so predominant in the Tongue River basin. The Tongue River Sandstone is the youngest of three "members" which form the Fort Union Formation, the other two members being the Lebo Shale Member and the Tullock Member.
The buff-colored sandstones and shales of the Tongue River sandstone are visible all along the greater part of the Tongue River from Dayton, Wyoming to a point north of Ashland, Montana. In this stretch, the sandstone layers of the Tongue River member hold ground water so that the highlands on each side of the Tongue River valley are often covered with pines. As the river approaches Miles City the valley changes appearance to grassy rolling hills, as the river leaves the Tongue River formation and flows through the Lebo shale and the Tullock sedimentary formations.
The Tongue River sandstone member outcrops widely over portions of southeast Montana and northeast Wyoming and it is best known for its coal. The Tongue River member has approximately 32 coal seams with a combined thickness in excess of 300 ft. The thickness of the separate coal seams varies radically from place to place—in some places the beds are thick but over a relatively short distance the seam can pinch out to nothing. Where these coal beds are thick and also close to the surface in the Powder River Basin in northern Wyoming and southern Montana they are mined in large open pit mines, like the mines along the Tongue in the vicinity of Decker, Montana. Tongue River coal is low in sulfur content and coal-fired electric generating places throughout the United States demand Tongue River coal so they can meet federal emission standards. Because of this demand, about 40% of the coal now used to generate electricity in the United States is mined from the Tongue River sandstone coal seams in the Powder River Basin, producing 14% of carbon dioxide emissions in the United States.
Where the Tongue River now flows in Montana and Wyoming, the sedimentary rock formation that is today known as the Tongue River sandstone began to form about 60 million years ago, when mountain uplifts began rising from a shallow sea. The Black Hills uplift on the east, the Hartville uplift on the southeast, and the Big Horn Block on the west created a flat, swampy low-lying plain, with slow moving rivers flowing northwest to deltas along a shallow sea. At this time the climate in the area was subtropical, averaging approximately of rainfall a year. For some 25 million years, the floor of this plain was made up of thick deposits of sandy silt from the surrounding mountains, with many rivers, deltas, backwaters and swamps, all covered by forests and vegetation. At that time, from 35 to 60 million years ago, the area where the Tongue River now flows would have appeared as a dense swampy jungle. Over long periods of time, the heavy plant growth died and accumulated as peaty layers in the large backwaters and swamps all across the basin. Periodically more sandy silt deposits would wash in from the mountains, completely burying the layers of organic peaty materials. Eventually the climate became drier and cooler. The area passed through more long periods of geologic time, during which new sedimentary layers buried this entire sandy silty layer along with its deposits of peat, under thousands of feet of newer sediments, compressing the sandy silty deposits into the Tongue River sandstone of today, and also compressing and changing the layers of peaty organic material into thinner layers of lignite coal. Over the last several million years, much of the overlying sediment has eroded away, bringing the sandstone layer with its seams of coal to the surface again in the Tongue River area.
The Tongue River sandstone forms cliffs, hills, buttes and bluffs along the river and throughout the basin."Roadside Geology of Montana", Davit Alt and Donald K. Hyndman, 1986, Montana Press Publishing Company, p. 399-402 From the Decker area downstream to about Birney the river flows through the prairie in a canyon carved from the Tongue River sandstone. The upper part of this canyon is dammed to form the Tongue River Reservoir.