Piute Reservoir

The Sevier River (pronounced "severe") is a -long river in the Great Basin of southwestern Utah in the United States. Originating west of Bryce Canyon National Park, the river flows north through a chain of high farming valleys and steep canyons along the west side of the Sevier Plateau before turning southwest and terminating in the endorheic basin of Sevier Lake in the Sevier Desert. It is used extensively for irrigation along its course, with the consequence that Sevier Lake is usually dry.

The Sevier River drainage basin of covers more than 13 percent of Utah and includes parts of ten counties, of which the river flows through seven. The name of the river is derived from the Spanish ''Río Severo'', "violent river". The Sevier is the longest river entirely within the state of Utah.

Course

The Sevier River is formed by the confluence of Minnie Creek and Tyler Creek in Long Valley in Kane County. The headwaters are at an elevation of between the Markagunt Plateau (on the west) and the Paunsaugunt Plateau. The river flows north through a wide valley into Garfield County passing Hatch and Panguitch. It then flows through the narrow, Circleville Canyon and enters Piute County at the town of Circleville, and is joined by the East Fork Sevier River at Kingston. Immediately north of Kingston, it is dammed to form Piute Reservoir.

The Sevier continues north past Marysvale and through Marysvale Canyon (or Sevier Canyon) into Sevier County. At Sevier the river enters the agricultural Sevier Valley, a long basin between the Pavant Range on the west and the Sevier Plateau to the east. In the valley, the Sevier River flows generally northeast, passing the cities and towns of Sevier, Joseph, Elsinore, Monroe, Central Valley, Anabella, Richfield, Glenwood, Venice and Sigurd. Just north of Sigurd, the river is dammed to form Rocky Ford reservoir. The Sevier River then continues north passing the towns of Aurora, Salina and Redmond, then flows north into Sanpete County where it picks up the San Pitch River near Gunnison.

In Juab County the Yuba Dam forms Sevier Bridge Reservoir, which also extends into Sanpete County. Below the dam the river flows north then turns abruptly west through Leamington Canyon, between the Canyon Mountains and Gilson Mountains, into Millard County. The river flows southwest across the Sevier Desert, where it is used heavily for irrigation in the Delta area, and is dammed at the DMAD and Gunnison Bend reservoirs. The river is essentially dry for the last below Delta, through its confluence with the also dry Beaver River before reaching the intermittent Sevier Lake bed.

Drainage basin

The Sevier River drainage basin is on the border of the Basin and Range Province and the Colorado Plateau; the north and west parts of the basin are defined by long linear mountain ranges such as the Pavant and Canyon Mountains. To the east and south rise high plateaus and block-shaped mountain ranges, chief of which are the Wasatch and Sevier Plateaus to the east, and the Paunsaugunt and Markagunt Plateaus, the Pink Cliffs and the Tushar Mountains to the south. The entire basin is at high elevation, with the highest point at Delano Peak in the Tushar Mountains. There are twelve other peaks in the basin rising more than . The lowest point is at Sevier Lake, above sea level.

The basin experiences a continental climate ranging in character from semi-arid to alpine. Precipitation – ranging from in the desert valleys to more than in the mountains – falls largely as snow during the winter and early spring, and as monsoon thunderstorms in late summer and early fall. As of 1999, there was an estimated annual runoff of in the Sevier River basin, but only about of that reached Sevier Lake, and mostly in wet years. Even before irrigation, however, not all of this water reached Sevier Lake due to large evaporation losses in the Sevier Desert.

The Sevier River basin is bordered to the south by the drainage basins of Virgin River, Kanab Creek, Paria River, and Dirty Devil River, all tributaries of the Colorado River. To the east, it is bordered by the Price and San Rafael River basins, tributaries of the Green River, which flows into the Colorado River. On the north, it is bordered by the Utah Lake–Great Salt Lake basin, and to the west, it is bordered by the Great Salt Lake Desert basins.

Most of the Sevier drainage is rural, composed of small farming communities. The largest town is Richfield, with a population of 7,723 as of 2016. About 69 percent of the land is federally owned, much of that in national forest lands such as the Manti-La Sal, Fishlake, Dixie, and Uinta National Forests. The basin also includes parts of Bryce Canyon National Park and Cedar Breaks National Monument. About 23 percent of the basin is privately owned and 8 percent is owned by the state of Utah.

The Sevier River corridor is a major transportation route, with U.S. Route 89 closely following the river for over from its headwaters as far as Gunnison, and I-70 paralleling the river for about between Sevier and Salina.

Geology

Surface rock in the Sevier River basin is composed mostly of Tertiary igneous rock and sedimentary rock ranging in age from Jurassic to Quaternary. This is underlain by marine sedimentary rock including thick limestone layers, which accumulated prior to the Jurassic when the western US was part of a shallow sea. Uplift during the Jurassic and Cretaceous thrust western Utah above sea level for the first time. Between 100 and 80 million years ago, the Sevier Orogeny created mountains much higher than those found in western Utah today. The Sevier Desert was formed starting about 20 million years ago due to crustal stretching that lowered the local terrain. Another period of uplift occurred towards the end of the Tertiary, about 12–2 million years ago, creating most of the present-day mountain ranges and plateaus.

Significant vertical displacement has occurred on several north–south faults in the basin. The Sevier Fault and Elsinore Fault run mostly parallel to the upper Sevier River above Gunnison, and the Paunsaugunt fault runs in the same general direction further east, passing through Bryce Canyon. The Sevier Valley (and the Sanpete Valley north of it) is a graben or down-thrown block of land between the Sevier and Elsinore faults, with deep alluvial deposits filling the valley bottom. Groundwater basins occur mostly in the alluvial valleys and have been estimated to hold up to of water.

Large mineral deposits occur in various areas of the basin, including coal in the Salina area, beryllium in the Delta area, and gypsum in the Richfield area. The dry Sevier Lake bed as well as deposits in the Redmond area, are a major source of salts, including halites and potassium sulfates. Historically, uranium was mined near Marysvale. Above Marysvale Canyon, the colorful formations of Big Rock Candy Mountain are a widely recognized geological site in central Utah; yellow, red and orange bands are the result of jarosite, hematite and pyrite while white bands result from alunite and kaolinite presence.

During the Pleistocene Ice Age and other preceding ice ages, the Sevier River flowed into Lake Bonneville, which covered more than of the eastern Great Basin. The Sevier Valley was underwater as far upstream as Richfield. As the lake receded with a drying climate at the end of the ice age, what is now the Sevier Desert became an independent lake, which drained into the Great Salt Lake via a now dry channel in Millard County north of Delta. As Sevier Lake shrank, the Sevier River formed a large delta at its mouth, hence the name of the modern town. Soils become progressively more alkaline and saline closer to Sevier Lake, the result of the river transporting minerals downstream over millennia as the lake receded. The largest sand dunes in Utah, found in Little Sahara Recreation Area, were formed from Sevier River delta deposits moved over thousands of years by prevailing winds.

There have been relatively recent volcanic activity in the Sevier basin between 1000 and 1500 AD, when basalt flows occurred on the Markagunt and Paunsaugaut Plateaus and in Pahvant Valley. One of these flows dammed a valley and formed Navajo Lake.

Plants and animals

Valley and stream habitats

Due to the semi-desert climate, the valleys of the Sevier River basin were historically mostly grassland and shrubland, with the seeds of ''Oryzopsis hymenoides

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