Calleguas Creek is the terminus of a river system in Ventura County, California. It drains the Calleguas Creek Watershed, an area 30 miles long and 14 miles wide, which includes Simi Valley, Moorpark, Camarillo and a large portion of Thousand Oaks. Tributaries include Arroyo Simi, Arroyo Santa Rosa, Revolon Slough and Arroyo Conejo. It discharges into the Pacific Ocean, the Santa Barbara Channel, at Mugu Lagoon on Naval Base Ventura County, just north of Point Mugu, where the Santa Monica Mountains meet the ocean, marking the southern/eastern boundary of the Oxnard Plain.