Boulder Creek is a 7.9-mile-long (13 km) stream tributary of the San Lorenzo River in the U.S. state of California.

Its main stem begins high in the Santa Cruz Mountains in Big Basin Redwoods State Park.

It flows generally southeast over approximately 7.9 miles (12.7 km) to its confluence with the San Lorenzo River.

It then turns sharply southwest at the intersection of SR 236 and Branson Ranch Road, where it receives a second unnamed tributary on the right bank.

The creek runs parallel with SR 236 from this convergence until it reaches its confluence with the San Lorenzo River.

It receives a third unnamed tributary on the left bank before flowing through the Boulder Creek Golf and Country Club and under West Hilton Drive.

It then flows into the San Lorenzo River 15 miles (24 km) from its mouth at the Pacific Ocean.