An explorer, politician, and soldier, John Charles Fremont is best known for his western explorations of 1842-44. In 1842 he was given the task of surveying the Oregon Trail up the Platte River. His second expedition led to results that solidified his fame. On this trek he circled the least-known parts of the West: from the Colorado Rockies to the South Pass, northwest to the Columbia River, south along the Cascade and Sierra Nevada ranges into California, and south before turning east across the desert to near Salt Lake City. His work proved the existence of Salt Lake and that the South Pass was the best route across the mountains.