Millard Canyon, located near the mouth of the Arroyo, is a delightful canyon with an impressive waterfall. Sunset Ridge The trail skirts the eastern side of the canyon, the eastern boundary of the Arroyo Seco Watershed. Millard Canyon was a major pedestrian thoroughfare for Tongva, Serrano people, and other Californian Native Americans traveling between the Los Angeles Basin coastal plain, the San Gabriel Mountains, and the Mojave Desert regions of Southern California.