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John Charles Fremont or Fremont (January 21, 1813 - July 13, 1890) was an American explorer, politician, and soldier who, in 1856, became the first candidate of the Republican Party for the office of President of the United States. During the 1840s, when he led five expeditions into the American West, that era's penny press and admiring historians accorded Fremont the sobriquet The Pathfinder. During the Mexican-American War, Fremont, a major in the U.S. Army, took control of California from the California Republic in 1846.

In the fall of 1853, Fremont embarked on another expedition to identify a viable route for a transcontinental railroad along the 38th parallel. The party journeyed between Missouri and San Francisco, California, over a combination of known trails and unexplored terrain. A primary objective was to pass through the Rocky Mountains and Sierra Nevada Mountains during winter to document the amount of snow and the feasibility of winter rail passage along the route. His photographer (daguerreotypist) was Solomon Nunes Carvalho.  Fremont followed the Santa Fe Trail, passing Bent's Fort before heading west and entering the San Luis Valley of Colorado in December. The party then followed the North Branch of the Old Spanish Trail, crossing the Continental Divide at Cochetopa Pass and continuing west into central Utah. But following the trail was made difficult by snow cover. On occasion, they were able to detect evidence of Captain John Gunnison's expedition, which had followed the North Branch just months before.  Weeks of snow and bitter cold took its toll and slowed progress. Nonessential equipment was abandoned and one man died before the struggling party reached the Mormon settlement of Parowan in southwestern Utah on February 8, 1854. After spending two weeks in Parowan to regain strength, the party continued across the Great Basin and entered the Owens Valley near present-day Big Pine, California. Fremont then journeyed south and crossed the Sierra Nevada Mountains and entered the Kern River drainage, which was followed west to the San Joaquin Valley.  Fremont arrived in San Francisco on April 16, 1854. Having completed a winter passage across the mountainous west, Fremont was optimistic that a railroad along the 38th Parallel was viable and that winter travel along the line would be possible through the Rocky Mountains.
John C. Frémont