The South Yuba River originates at Lake Angela in Nevada County about three quarters of a mile north of Donner Pass, about three miles east of the town of Soda Springs. After passing through Lake Van Norden with Upper Castle Creek (longer than the Lake Angela stem) entering from the right, it gathers numerous snow-fed tributaries running west through a marshy, lake-filled valley, crossing Interstate 80 several times. The river briefly enters Placer County before flowing back north into Nevada County, then flows into Lake Spaulding, where much of its water is diverted south to the Bear River drainage. The remainder of the river turns northward into a gorge near Emigrant Gap before continuing west. It receives Canyon Creek from the right, then receives Poorman Creek also from the right near Washington. The river continues west into the foothills and into South Yuba River State Park where it is bridged by State Route 49. It joins the Yuba River at the upper end of Englebright Lake.