The first reported European visitor to the Las Vegas Valley was Raphael Rivera in 1829. Las Vegas was named by Spaniards in the Antonio Armijo party,who used the water in the area while heading north and west along the Old Spanish Trail from Texas. In the 19th century, areas of the valley contained artesian wells that supported extensive green areas or meadows (vegas in Spanish); hence the name Las Vegas.
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 that served as a stopover for travelers along the "Mormon Corridor" between Salt Lake and the briefly thriving colony of saints at San Bernardino, California. Mormons abandoned Las Vegas in 1857, during the Utah War. Las Vegas was established as a railroad town on May 15, 1905, when 110 acres (45 ha) owned by the San Pedro, Los Angeles and Salt Lake Railroad was auctioned off in what is now downtown Las Vegas. Among the railroad's most notable owners and directors were Montana Senator William A. Clark, Utah U.S. Senator Thomas Kearns, and R.C. Kerens of St. Louis.Las Vegas was part of Lincoln County until 1908, when it became part of the newly established Clark County. The St. Joan of Arc Catholic Church near 4th and Bridger in downtown was founded in 1910. Las Vegas became an incorporated city on March 16, 1911; Peter Buol was the first mayor. Las Vegas started as a stopover on the pioneer trails to the west, and became a popular railroad town in the early 20th century. It was a staging point for mines in the surrounding area, especially those around the town of Bullfrog, that shipped goods to the rest of the country. With the proliferation of the railroads, Las Vegas became less important, but the completion of the nearby Hoover Dam in 1935 resulted in growth in the number of residents and increased tourism. The dam, located 30 mi (48 km) southeast of the city, formed Lake Mead, the US's largest man-made lake and reservoir. Today, tours are offered into lesser-known parts of the dam. The legalization of gambling in 1931 led to the advent of the casino hotels for which Las Vegas is famous. Major development occurred in the 1940s, "due almost entirely" to the influx of scientists and staff from the Manhattan Project, an atomic bomb research project of World War II. Atomic test watching parties were sometimes thrown. American organized crime figures such as Benjamin "Bugsy" Siegel and Meyer Lansky managed or funded most of the original large casinos. The rapid growth of Las Vegas is credited with dooming Galveston, Texas; Hot Springs, Arkansas; and other major gaming centers in the 1950s.[
