Serrano Creek is a roughly 7.5 miles (12.1 km) tributary of San Diego Creek

San Diego Creek

San Diego Creek is a waterway flowing into Upper Newport Bay in central Orange County in the U.S. state of California. Its basin covers in parts of eight cities, including Irvine, Tustin, and Costa Mesa. The major tributary of the northeast-flowing stream is Peters Canyon Wash, which joins a few...

 in the U.S. state

U.S. state

A U.S. state is any one of the 50 federated states of the United States of America that share sovereignty with the federal government. Because of this shared sovereignty, an American is a citizen both of the federal entity and of his or her state of domicile. Four states use the official title of...

 of California

California

California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...

. The creek starts in the Santa Ana Mountains

Santa Ana Mountains

The Santa Ana Mountains are a short peninsular mountain range along the coast of Southern California in the United States. They extend for approximately 36 mi southeast of the Los Angeles Basin largely along the border between Orange and Riverside counties.- Geography :The range starts in the...

 in a canyon in Whiting Ranch Wilderness Park, near the boundary of the Cleveland National Forest

Cleveland National Forest

Cleveland National Forest encompasses 460,000 acres , mostly of chaparral, with a few riparian areas. A warm dry mediterranean climate prevails over the Forest. It is the southernmost National forest of California. It is administered by the United States Forest Service, a government agency within...

. It then flows southwest into the city of Lake Forest

Lake Forest, California

Lake Forest is a city in Orange County, California. The population was 77,264 at the 2010 census.Lake Forest incorporated as a city on December 20, 1991. Prior to a vote of the residents in that year, the community had formerly been known as El Toro since the 1880s...

, running in a channelized course roughly parallel to Aliso Creek. It abruptly turns northwest then southwest at 90-degree angles as it enters a large storm drain

Storm drain

A storm drain, storm sewer , stormwater drain or drainage well system or simply a drain or drain system is designed to drain excess rain and ground water from paved streets, parking lots, sidewalks, and roofs. Storm drains vary in design from small residential dry wells to large municipal systems...

 that takes it the rest of the way to the confluence with the La Cañada Channel, creating the main stem of San Diego Creek.