Aliso Canyon, Canyon in the San Joaquin Hills, California, US

Aliso Canyon is a 6.5-mile water gap cut by Aliso Creek through the San Joaquin Hills of Orange County, running from near Laguna Niguel Regional Park to its outlet at Laguna Beach. About 800 feet deep on average and 1.5 miles wide at its widest, it has three sections, from a broad upstream stretch to a narrow gorge near the ocean. Its floor is filled with alluvium up to 300 feet thick, and Wood Canyon joins it about 5 miles upstream of the sea.

Aliso Canyon's northern divide once marked a boundary between the Acjachemen and Tongva peoples, and many Acjachemen archaeological sites have been found in the canyon. From the Spanish conquest until the early 20th century, its fertile alluvial soil and grasslands were used for orchards and grazing. Since the 1970s it has been the centerpiece of Aliso and Wood Canyons Wilderness Park.

The name aliso comes from the Spanish word for alder, the trees that once lined Aliso Creek. The canyon's northern divide marked the boundary between the Acjachemen and Tongva peoples, and many Acjachemen archaeological sites have been found in the canyon. Since the 1970s the canyon has been the centerpiece of Aliso and Wood Canyons Wilderness Park.

Aliso Canyon is reached on foot or by bike via the paved Aliso Creek Trail, which runs along one side of the creek; a separate unpaved private road on the opposite bank leads to a wastewater treatment plant and is not open to visitors. The canyon lies between Laguna Beach, Laguna Niguel and Aliso Viejo, with trail access from Aliso and Wood Canyons Wilderness Park. Expect a deep, eroded creek channel and stands of giant reed along the valley floor.

Aliso Canyon's valley floor looks like an aged U-shaped glacial valley, but it was cut by Aliso Creek and later filled with alluvium up to 300 feet (91 m) deep. The canyon may have formed as recently as the Wisconsin glaciation, between 60,000 and 10,000 years ago, when the San Joaquin Hills rose and a wetter climate gave the creek great erosive force.