The San Luis Rey River is a river located in southern California, primarily flowing through San Diego County. It originates in the Palomar Mountain range and travels approximately 75 miles before emptying into the Pacific Ocean near the city of Oceanside. The river's watershed supports various ecosystems and wildlife. Historically, the San Luis Rey River was significant for the indigenous Luiseño people and later became important for agriculture and development in the region. Today, the river is a vital resource for local communities, providing water for irrigation and recreational opportunities along its banks.