San Diego Creek - Course

Course

San Diego Creek rises in the extreme foothills of the Santa Ana Mountains near El Toro, Lake Forest. Most of its upper course is culverted under residential subdivisions of El Toro and Irvine. It flows northeast, fed by tributaries from the northern extent of Laguna Canyon and from the Santa Ana Mountains to the north of the creek. After crossing under Interstate 405, the creek immediately becomes channelized and receives Serrano Creek via an underground culvert on the right bank. Directly after the confluence, it crosses through five box-cut culverts beneath California State Route 133. It then flows northeast in a nearly straight course through East Irvine and the City of Irvine, receiving several larger tributaries on the right bank. In order from upstream to most downstream, these are Agua Chinon Creek, Bee Canyon Wash, and the Marshburn Channel, all of which run south-southwest in a channelized course to San Diego Creek. A few miles past the confluence with Marshburn, San Diego Creek receives its major tributary, Peters Canyon Wash, on the right bank. The wash begins at Peters Canyon Reservoir in the Santa Ana Mountains and runs about 10 miles (16 km) south-southwest. Although historically it was a smaller tributary, due to present-day flood control purposes, the channel of Peters Canyon is wider than the channel of San Diego Creek when they join.

At the confluence with Peters Canyon, San Diego Creek turns abruptly southwest, flowing underneath Interstate 405 for the second time. After flowing beneath the highway, San Diego Creek enters a series of slackwater pools, held back by small weirs and drop structures, in the San Joaquin Wildlife Sanctuary. The partially man-made marsh stretches approximately 1.4 miles (2.3 km) to where San Diego Creek turns abruptly westward. The creek receives Bonita Creek on the left bank just a few hundred yards upstream frow where it outlets into Upper Newport Bay, which eventually discharges into the Pacific Ocean.