Aliso Creek

Aliso Creek is a 19.8-mile -long, mostly urban stream in south Orange County, California. Originating in the Cleveland National Forest in the Santa Ana Mountains, it flows generally southwest and empties into the Pacific Ocean at Laguna Beach. The creek's watershed drains 34.9 square miles , and it is joined by seven main tributaries. As of 2018, the watershed had a population of 144,000 divided among seven incorporated cities.
Aliso Creek flows over highly erosive marine sedimentary rock of late Eocene to Pliocene age. What would become the Aliso Creek watershed originally lay at the bottom of the Pacific Ocean, before being uplifted as recently as 10 million years ago. About 1.2 million years ago, the San Joaquin Hills began to uplift in the path of Aliso Creek. Occasionally swollen by wetter climates during glacial periods, the creek carved the deep water gap known today as Aliso Canyon, the main feature of Aliso and Wood Canyons Wilderness Park.

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