The State of Deseret was established, provisionally, by leaders of the Church of Latter Day Saints (LDS). Deseret came from lands which included parts of what became California, Utah, Nevada, Colorado, Idaho, Oregon, and Wyoming, all of which had been recently seized from Mexico in the Treaty of Guadalupe, which ended the Mexican War.
In 1849 ,LDS elders, led by Brigham Young, copied large parts of the state constitution of Iowa (where they had resided for a time during their trek westward) and dispatched it to the Congress in the hope of acquiring statehood (and lands) before California and New Mexico achieved statehood. Under the LDS proposal Los Angeles and San Diego, then barely villages, would have become part of the State of Deseret.
Statehood in the antebellum days required more than just the demands presented in the Constitution. Congress was acutely aware of the need to maintain the status quo regarding the balance between pro-slavery and anti-slavery votes in Washington. This alone gave pause to those considering Young’s proposal, the Mormon position on polygamy was also difficult for many eastern lawmakers to consider.
President Zachary Taylor – a southerner from Louisiana – proposed combining California and Deseret into a single state, an act which would help to retain the balance of pro and anti-slavery votes. California leaders rejected this proposal out of hand. In 1850, as part of the Compromise of 1850, Congress created the Utah Territory out of some of the land included in the provisional State of Deseret. Mormon leaders accepted the reduced territory but continued to propose statehood using the basic constitution written for Deseret.
Once the transcontinental railroad traversed Utah territory the drive for a separate state based on LDS morality and law lost traction. The provisional government of Deseret remained the governing authority of the Utah Territory until 1872 despite several attempts to write a new constitution which would lead to Utah statehood. Utah finally became a state – the 45th – in 1896, after their 1890 Manifesto which banned polygamy.