Once populated by Native Americans Mariposa came into existence almost overnight via the deluge of immigrants seeking their fortunes during the Gold Rush. The Gold Rush at one time created a population greater then what resides in Mariposa today. On February 18, 1850 Mariposa became the largest county of the original 27 California counties. Later the county was split up and now occupies 1,455 square miles of California's rich Mother Lode country. Mariposa is the Spanish name for butterfly, and aptly named by Lieutenant Gabriel Moraga of the Mexican Army in 1806 for the swarms of butterflies he saw along Mariposa Creek. John C. Fremont, an early explorer, is responsible for founding the town whose many streets are named after his family members. In 1854 the famous courthouse was built on land donated by Fremont. In 1907 construction was started on the Yosemite Valley Railroad. The railroad employed as many as 1,500 men during the early years. The railroad ran from 1907 until 1945 hauling logs, limestone and other mineral. In later years as Yosemite grew in popularity the railroad shuttled tourists to the new wonder. The railroad parallels the north bank of the Merced River which starts at 11,000 feet in the Yosemite Valley. The river was named by Lieutenant Gabriel Moraga when he and his soldiers had just completed a 40 mile march. He named the river El Rio Nuestra Senora de la Merced (The River of Our Lady of Mercy). Attempts are under way to reconstruct the railroad following much the same route. Yosemite, first inhabited by Native Americans, was first seen by settles immigrating west for the gold rush when on March 21, 1851 Major Savage pursing "Indians" came across the grandeur of the valley. Yosemite is a spectacular valley filled with waterfalls, glacier eroded spires of granite, plush meadows, meandering streams and incredible variety of wildlife including California's famous bears. The National Park presents to the public an incredible setting to discover the history of the valley.