<P> The Merced River drops over Nevada Falls and Vernal Falls, together known as the "Giant Staircase", then receives Illilouette Creek and flows into Yosemite Valley, where it meanders between pine forests and meadows that fill the valley floor . Tenaya, Yosemite, Bridalveil and Pigeon Creeks join the Merced River in Yosemite Valley . Beyond the glacial moraine at the western end of the valley the river flows through the steep Merced River Canyon, picks up Cascade Creek and turns south near El Portal . State Route 140 follows the river out of the west entrance to the national park, a few miles before the South Fork Merced River, the largest tributary, joins from the left . </P> <P> The river arcs northwest to receive the North Fork, and a few miles after it enters Lake McClure, formed by New Exchequer Dam . Below New Exchequer, the river flows west through a heavily irrigated region of the Central Valley, passing through McSwain and Crocker - Huffman Dams and the cities of Hopeton, Delhi and Livingston . It joins the San Joaquin River at Hills Ferry, a few miles south of Turlock . </P> <P> The Merced River watershed encompasses 1,726 square miles (4,470 km) in the central Sierra Nevada . To the north it is bordered by the watershed of the Tuolumne River, the other major river draining Yosemite National Park . On the south, the Merced watershed borders on the headwaters of the San Joaquin River . To the east, it is bordered by the Sierra crest which divides it from the endorheic Great Basin watershed of Mono Lake . </P> <P> Much of the Merced River basin is at high elevation, where an alpine climate prevails . The Sierra receives heavy snowfall in the winter, which melts in the spring and early summer causing annual flooding . By late autumn the river level has dropped considerably, and some smaller tributaries dry up altogether . Up to 85% of the flow above Happy Isles comes from melting snow . In the dry season, groundwater provides the only base flow to the river . In addition, the river is fed by dozens of high Sierra lakes, the largest of which include Merced Lake, Tenaya Lake, Ostrander Lake, the Chain Lakes, and May Lake . The foothills experience a drier Mediterranean climate, while the San Joaquin Valley floor is dry enough to be considered semi-desert . </P>

Where does the merced river start and end