American River
The North Fork is the longest tributary of the American River, at . It begins at an elevation of about near Lake Tahoe in Placer County at Mountain Meadow Lake, just northeast of Granite Chief and immediately due west of Squaw Valley Ski Resort. It flows westward through remote wilderness areas.
South Fork American River
The South Fork drains an area of , or about a third of the American River watershed. Major tributaries include Silver Creek, Rock Creek, Weber Creek, and Silver Fork American River. Most of the watershed consists of high, forested mountains and steep-sided valleys that receive up to of annual precipitation, except for the westernmost section which consists of drier foothill country. The river also contributes about a third of the total outflow of the American River system.