The Vernal Unit is located near the city of Vernal in the Ashley Valley of northeastern Utah and lies within the Green River Basin of the Upper Colorado River Basin. The Vernal Unit provides supplemental irrigation water to land in Ashley Valley of eastern Utah, as well as municipal and industrial water to local communities. The primary storage feature of the Vernal Unit is Steinaker Dam which impounds 38,000 acre-foot capacity Steinaker Reservoir located 3.5 miles north of Vernal, Utah. Steinaker Dam is a zoned earthfill structure with a height of 162 feet, a crest length of 1,997 feet, and a volume of 1,892,000 cubic yards of material. Other principal features of the Vernal Unit include Fort Thornburgh Diversion Dam on Ashley Creek and Steinaker Feeder Canal. Excess spring flows from Ashley Creek are diverted by Fort Thornburgh Diversion Dam on Ashley Creek, four miles northwest of Vernal. From the diversion dam, the water is conveyed eastward to Steinaker Reservoir through the 2.8 mile-long Steinaker Feeder Canal. Reservoir water is released to Steinaker Service Canal and conveyed south 11.6 miles to existing canals and ditches to provide supplemental irrigation water to approximately 14,781 acres. This water partially replaces Ashley Creek water, including releases from privately constructed reservoirs upstream. Some of the replaced water is used on lands upstream of Steinaker Service Canal and some is diverted from Ashley Springs on Ashley Creek into the municipal pipelines through which about 1,600 acre-feet of water is delivered annually to the communities of Vernal, Naples, and Maeser. Prior to construction of the Vernal Unit features, flows in Ashley Creek dwindled to an inadequate water supply by late summer. The Vernal Unit, along with the Jensen, Bonneville, and Upalco Units, was authorized by the 1956 Colorado River Storage Project Act. Construction of Vernal Unit irrigation facilities started on May 14, 1959 and was completed in 1963. Project facilities were turned over to the Uintah Water Conservancy District for operation and maintenance on January 1, 1967. Construction of drainage facilities was initiated in 1970 and completed in 1977. Modifications were made to the drainage facilities in 1982. In 1993, Steinaker Dam and Reservoir began modifications to comply with the Safety of Dams requirements. These modifications included excavating the clay foundation material located downstream of the toe of the dam. Dam modification was completed in September of 1994. The construction resulted in a stability berm at the downstream toe.