After the United States victory in the Mexican-American War (1846-1848), both countries signed a treaty giving the U.S. nearly half of Mexico’s original sovereign territory. When the question of California’s geographical size and official borders came up at the state’s first Constitutional Convention in October 1849, there were two main options considered. One called for including all of what Mexicans called Alta (Upper) California, an enormous chunk of land that extended from the Pacific Ocean east all the way to the Rocky Mountains and north to the 42nd parallel.
Many of the delegates, however, preferred a more manageable border near the Sierra Nevada, for both political and practical reasons. The possibility of a large state later being politically carved into slave territories was one serious concern. Others pointed out it would be a mistake to incorporate land where the Church of Latter-Day Saints had established its home base without the Mormons having representation at the convention. Among those pushing for a boundary near the Sierra Range was none other than the legendary topographical engineer, John C. Frémont, credited as the first Euro-American, along with his cartographer Charles Preuss, to see Lake Tahoe.