Aliso Canyon in Laguna Beach is a major break in the San Joaquin Hills, formed by Aliso Creek and likely carved as recently as the last ice age before rising seas and sediment created its broad valley floor. Long a natural and human boundary, its northern divide once separated the Acjachemen and Tongva, and many archaeological sites reflect Acjachemen occupation. After Spanish colonization disrupted Native life, the canyon supported ranching and orchards, including land within Juan Avila’s Rancho Niguel in the 1840s. Much of it is now protected wilderness with diverse habitats, wildlife, and significant Miocene fossils, though modern runoff and pollution have damaged the creek and riparian areas.