During the 1950s other large companies, including Shell, Superior, and Texas Oil, tapped into an oil region in southeastern Utah that overshadowed even the Uinta Basin. The discovery well was at Aneth, along the San Juan River east of the old Mexican Hat field, and produced 1,704 barrels of oil a day after it hit oil in 1956. During that year twenty other wells in the area were completed, each averaging a daily flow of 800 barrels of oil. The major companies operating in close proximity to the Aneth region soon discovered several other fields, and together these fields became known as the Greater Aneth Area.
From the late 1940s until 1975 almost all of Utah's oil development occurred in an area extending down the eastern border of the state from the Uinta Basin to the San Juan River. The one exception to this was the Upper Valley oil field, which is located ten miles southeast of Escalante in Garfield County. In 1964 Tenneco opened the Upper Valley field. By 1978 there were twenty-six active wells that were capable of producing a total of one million barrels of petroleum a year.
In 1975 Summit County became an important center for oil development. As part of the Overthrust Belt, a region of highly complex mountain-forming faults and thrusts, Summit County became the scene of American Quasar's discovery at a field called Pineview, east of Coalville. Within the next five years Amoco, Chevron, Gulf, Champlin, and Anschutz Corporation hit large amounts of oil and gas in a series of fields that included Lodgepole, Elkhorn Ridge, Anschutz Ranch, and Anschutz Ranch East.