Oceanside, California, a city in San Diego County. It is on the Gulf of Catalina, 40 miles (64 km) northwest of San Diego. It is primarily a resort city but has some industry. San Luis Rey Mission, founded in 1798, is here. Camp Pendleton, a U.S. Marine Corps base, adjoins the city. Oceanside was incorporated as a city in 1888. It has the council-manager form of government.