Most folks know that Mormons settled Utah. They arrived in 1847 led by Brigham Young. Young and his religious followers were and are many things to many people but this leader's role as a colonizer finds few peers.Young and the Mormons had been driven out of Illinois, Missouri and other areas of the Eastern States after their original prophet-leader, Joseph Smith, was killed by a mob in Carthage, Illinois. Young was determined to create a sanctuary where he and his followers could worship and live as they believed.
When they arrived in the West most of it below the 42nd Parallel belonged to Mexico. The 1848 Treaty of Guadalupe Hidalgo at the end of the Mexican War ceded what is now Utah, Nevada, New Mexico, Arizona and California to the United States. Young wasted no time and proposed the Provisional State of Deseret in 1849.
As seen from the map here (taken from a version developed by Dale Morgan (1947) and published in Rocks, Rails and Trails by Paul K. Link and E. Chilton Phoenix) the boundaries of the proposed state covered most of the Great Basin and Colorado River Drainage. Young used these natural watershed borders as logical boundaries and extended the eastern borders to the Continental Divide south to the Gila River and to the western coast south of present day San Diego. This southern border paralleled the northern Mexican border of that era.
Young was also economically astute and included and ocean port within the boundary before it moved west along the eastern drainages of the Sierras and the northern Great Basin watersheds including that of the Bear River. This marks the first and only time this kind of boundary-making was officially registered for statehood in the U.S. But it was not to be.
With the Compromise of 1850 California was admitted to the Union (although technically created in 1849) and the Territories of New Mexico and Utah were created. Oregon Territory was created in 1848 and the proposed Deseret would have encroached on some of its southern border.
As an official territory, Utah was unlike its neighbors in that it kept a separate, church-sponsored active legislature and government as Deseret with its official one until 1880. It tried three more times to gain official state recognition failing each time in the face of national distrust of Mormon Church wielded government power and the now in-the-open church practice of Polygamy.
By gaining statehood first, Colorado and Nevada started nibbling away at Utah Territory in 1861. Nevada would take two more bites and Colorado and Wyoming got their chunks before Utah renounced the practice of polygamy and was able to reassure congress that the Mormon Church would be kept at a respectable distance from direct involvement with state government. In 1896 Utah finally achieved statehood with the borders as we see them today.
