The Trinity River rises in northeastern Trinity County, in the Shasta-Trinity National Forest along the east side of the Scott Mountains, a subrange of the Klamath Mountains. It flows south-southwest along the west side of the Trinity Mountains into Trinity Lake (20 miles long) formed on the river by the Trinity Dam, then immediately into the smaller Lewiston Lake, formed by the Lewiston Dam at Lewiston. From the reservoir it flows generally west-northwest past Weaverville and along the southern side of the Trinity Alps. It receives the New River from the north at Burnt Ranch and the South Fork Trinity River from the south along the Humboldt-Trinity county line. From the confluence with the South Fork it flows generally north-northwest through the Hoopa Valley Indian Reservation and joins the Klamath from the south in northern Humboldt County at Weitchpec, approximately 20 miles from the Pacific coast. Both Trinity Lake and Lake Lewiston are within Whiskeytown-Shasta-Trinity National Recreation Area.