West of Red Rock Canyon the river leaves Los Padres National Forest and its valley widens considerably. Kelly Creek joins from the south, draining Los Laureles Canyon and Cold Spring Canyon. State Route 154, which crosses the Santa Ynez Mountains via San Marcos Pass, enters the Santa Ynez River valley at this point and follows the river for several miles to the west. Hot Spring Canyon joins from the south just before the Santa Ynez River enters Lake Cachuma.