 Even before the establishment of Yosemite National Park , tourists began to travel into the Merced Canyon and Yosemite Valley as early as 1855 . The first roads were constructed into Yosemite Valley in the 1870s . The first was <unk> Road , followed by Big Oak Flat Road , a trading route from Stockton to Merced Canyon . Environmental movements led by John Muir and Robert Underwood Johnson convinced the U.S. Congress to establish Yosemite National Park in 1890 . With the creation of the national park tourism to the Valley and the Merced River increased significantly , leading to many other roads being built throughout the upper Merced River watershed . Other national forests protecting more of the Merced River upper basin followed , including Sierra National Forest and Stanislaus National Forest . 
