Zion was little visited by outsiders during the 19th Century, but the region's isolation began to erode in 1908 when Deputy Surveyor Leo Snow mapped the upper Virgin River for the U.S. Department of the Interior. Snow's report was so persuasive that President W.H. Taft created Mukuntuweap National Monument the next year. Major John Wesley Powell, who explored the area in the 1870s, had assigned the name Mukuntuweap, derived from a Paiute word, but local residents preferred the name Zion, and in 1918 the monument's name was changed. By 1919, it had been enlarged and renamed Zion National Park. Zion's remoteness at first limited visitation, but access improved in 1923 when the Union Pacific Railroad brought service to Cedar City and the State of Utah built a road into Zion Canyon. Visitation increased again in 1930 with completion of the Zion-Mt. Carmel Highway and tunnel. During the Depression of the 1930s, the Civilian Conservation Corps made substantial contributions by constructing roads, trails, and buildings throughout the park, leaving distinctive stone and timber structures still visible today.