The South Fork Merced begins high on the south flank of Triple Divide Peak, at roughly 10,600 feet. This is the alpine Sierra at its most austere -- bare granite, thin air, snowfields that linger into July. Triple Divide Peak earns its name by sending water in three directions, and the South Fork collects from the southwestern slopes along with runoff from Gale Peak and Sing Peak. The young river runs southwest through pine forest, flanked by granite cliffs that gradually tighten into a deep canyon. The transformation from alpine trickle to canyon river happens quickly here. Within a few miles, the walls close in and the forest canopy narrows overhead, and the sound of water echoing off stone becomes the dominant feature of the landscape.

The canyon opens abruptly into a large, bowl-shaped valley -- a geological surprise after miles of constriction. Here the river passes the north side of Wawona, one of Yosemite's oldest settled areas, and receives Chilnualna Creek from the right. Wawona has been a waypoint for travelers since the 1850s, and the South Fork's broad valley provided the flat ground and water that early settlers needed. The river passes beneath Wawona Road, which serves as the south entrance to Yosemite National Park, connecting the park to the communities below. For most visitors driving in from the south, this is their first encounter with a Yosemite waterway -- though few realize the river beside the road has already traveled miles through wilderness that almost no one sees.

Below Wawona, the South Fork drops into another gorge -- broader and deeper than the upper canyon. The river turns north, collecting Alder Creek, Rail Creek, Big Creek, and Bishop Creek, all entering from the right as the drainage widens. Each tributary adds volume; by this stretch, the South Fork carries an average flow of 356 cubic feet per second at its mouth. The gorge represents the river's most remote section. No roads follow the water here, and the terrain is steep enough to discourage all but determined hikers. Eventually the river swings west, crossing the boundary between Yosemite National Park and the Sierra National Forest, leaving protected wilderness for the managed timberland of the lower Sierra foothills.

The South Fork meets the Merced River about 25 miles downstream of Yosemite Valley's western end. Of the South Fork's 240-square-mile drainage basin, 109 square miles lie within the national park -- nearly half the watershed is federally protected. The river is designated as a Wild and Scenic River, a recognition that its free-flowing character and outstanding natural values warrant preservation. Unlike the main stem of the Merced, which passes through the famous valley and draws millions of visitors, the South Fork flows through country that most people never see. Its canyon lacks the towering monoliths that define Yosemite's iconic scenery, but the geology is the same Sierra granite, carved by the same glacial and hydrological forces. The difference is simply fame -- one river got Ansel Adams and presidential attention, and the other got a wrong name on a map that took years to correct.