John C. Frémont traveled into the Las Vegas Valley on May 3, 1844, while it was still part of Mexico. He was a leader of a group of scientists, scouts and observers for the United States Army Corps of Engineers. On May 10, 1855, following annexation by the United States, Brigham Young assigned 30 missionaries of The Church of Jesus Christ of Latter-day Saints led by William Bringhurst to the area to convert the Paiute Indian population to Mormonism. A fort was built near the current downtown area, serving as a stopover for travelers along the "Mormon Corridor" between Salt Lake and the briefly thriving colony of "saints" at San Bernardino, California. Las Vegas was established as a railroad town on May 15, 1905, when 110 acres (44.5 ha) owned by Montana Senator William A. Clark's San Pedro, Los Angeles and Salt Lake Railroad, was auctioned off in what is now downtown Las Vegas. Las Vegas was part of Lincoln County until 1909 when it became part of the newly established Clark County.