The cleverly-named River Trail follows the east side of the Upper Sacramento River from just north of the Castle Crags State Park campground to a dead-end 1½ miles upstream.
One way to begin is by parking about ¼ mile north of the Castella exit on Interstate 5 along the frontage road on the east side of the freeway. A gap in the fence leads down a short trail to an underpass below the railroad tracks and then a swaying suspension bridge [shown above] over the river, with the trailhead just beyond.
Almost all of the trail is in a shady forest at river level, with only a few short climbs to avoid riverside cliffs. If you enjoy seeing fall colors on bigleaf maple, vine maple [shown above], and especially Indian Rhubarb, this is the hike to go on in October.
Several creeks flow into the river along the trail; each seemingly topped with a bridge of a different design — even in a dry year the whole area is moist and green.