Aliso Creek (Orange County) - Course

Course

Aliso Creek rises in the foothills of the Santa Ana Mountains, near the community of Portola Hills, part of Lake Forest, and at the boundary of the Cleveland National Forest. The Loma Ridge rises about 1,500 feet (460 m) above the creek's headwaters, which are at an elevation of 2,300 feet (700 m). There is no pond, lake or spring at the creek's ultimate source; it starts out as a small seasonal gully that courses southwards through a small valley with relatively little development. The creek then continues generally southwest for 19 miles (31 km) to the Pacific Ocean at Laguna Beach, collecting water from seven major tributaries and over forty minor drains and streams. For much of its course, the creek is channelized and confined by urban development. It only flows freely in several stretches in its far upper and lower course. Passing south of several residential areas on the foothills to the north, Aliso Creek and El Toro Road run parallel for much of the creek's length upstream from Interstate 5. Flowing southwest in a small ravine along the right side of the road, the creek soon passes underneath the twin bridges of California State Route 241, and receives from the right an unnamed northern fork. At this confluence, the creek turns more to the south, then crosses under El Toro Road and bisects another residential area. As it enters the city of Lake Forest, it receives from the right Munger Creek and from the left English Canyon Creek, a larger tributary which drains part of the city of Mission Viejo, 16 miles (26 km) from the mouth.

The creek crosses under Trabuco Road and Jeronimo Road; the latter was once the site of a stream gauge. It makes a bend to the southeast then veers back south, entering a large gulch and crossing beneath Interstate 5. The creek then enters a culvert beneath Paseo de Valencia, then crosses under Laguna Hills Drive and cascades under Moulton Parkway, through the community of Laguna Hills. It then swings to the southeast and receives the Aliso Hills Channel, which enters from the left, 13 miles (21 km) from the mouth. The Aliso Hills Channel drains much of eastern Laguna Hills, western Mission Viejo, and southeastern Lake Forest. From the confluence, the gradient of the creek flattens sharply and the stream enters a broad and shallow valley that runs between Aliso Creek Road on the west and Alicia Parkway on the east. It passes under California State Route 73, which crosses the valley on an earthfill and a bridge segment. The creek receives from the right the Dairy Fork, 9 miles (14 km) from the mouth, which drains parts of southern Laguna Hills and northeastern Aliso Viejo. The southwest-flowing Dairy Fork once flowed in a prominent canyon that was filled in the 1960s and 1970s to build the city of Aliso Viejo; State Route 73 now runs above the former canyon.

After receiving the fork, Aliso Creek passes into three massive culverts that cross under Pacific Park Drive, which crosses also on an earthfill. Flowing past several sports complexes, it begins to form the boundary of Aliso Viejo and Laguna Niguel, then crosses under Aliso Creek Road into Aliso and Wood Canyons Regional Park. Here, it receives from the left its largest tributary, Sulphur Creek. This creek is about 4.5 miles (7.2 km) long and drains a fair portion of northern Laguna Niguel, 7 miles (11 km) from the mouth. From there, Aliso Creek bends west and enters Aliso Canyon, which cuts through the San Joaquin Hills on the creek's final run to the sea. About 1 mile (1.6 km) downstream of the Sulphur Creek confluence, the creek is briefly impounded behind a small dam, and receives the south-flowing Wood Canyon Creek, the second largest tributary, 5 miles (8.0 km) from the mouth. Wood Canyon Creek drains the largest arm of Aliso Canyon and most of eastern Aliso Viejo. Flowing almost due south through a valley with slopes dissected by many deep side canyons, Aliso Creek turns sharply west as it enters private property less than 1 mile (1.6 km) from the mouth. This section of the canyon is known for flooding frequently. The creek then enters a small lagoon, crosses under the Pacific Coast Highway and enters the Pacific Ocean.