Arizona states of Sonora and Baja California. Arizona is the 48th state and last of the contiguous states to be admitted to the Union, achieving statehood on February 14, 1912, coinciding with Valentine's Day. Historically part of the territory of "Alta California" in New Spain, it became part of independent Mexico in 1821. After being defeated in the Mexican–American War, Mexico ceded much of this territory to the United States in 1848. The southernmost portion of the state was acquired in 1853 through the Gadsden Purchase. Southern Arizona is known for its desert climate, with very hot summers and mild winters.
Admission to the Union President would issue a proclamation announcing that a new state has been added to the Union. While Congress, which has ultimate authority over the admission of new states, has usually followed this procedure, there have been occasions (due to unique case-specific circumstances) where it did not. Congress is under no obligation to admit states, even in those areas whose population expresses a desire for statehood. In one instance, Mormon pioneers in Salt Lake City sought to establish the state of Deseret in 1849. It existed for slightly over two years and was never approved by the United States Congress. In