The Santa Monica Mountains NRA contains 154,095 acres (62,360 ha) in the Santa Monica Mountains of the Transverse Ranges between the Pacific Ocean and inland valleys. Its southeastern slopes are part of the headwaters of the Los Angeles River. The California State Park system owns 42,000 acres (17,000 ha), the National Park Service controls 21,500 acres (8,700 ha), and the rest of the SMMNRA lands are in local agencies parks, university study reserves, and private property conservation easements. In size the Santa Monica Mountains National Recreation Area is the largest urban national park in the United States. The Santa Monica Mountains National Recreation Area was established November 10, 1978, after a long campaign for preservation of the Santa Monica Mountains by local and regional conservationists
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