Its southeastern slopes are part of the headwaters of the Los Angeles River .
The Santa Monica Mountains NRA contains 156,671 acres ( 63,403 ha ) in the Santa Monica Mountains of the Transverse Ranges between the Pacific Ocean and inland valleys .
NRA 's southeastern slopes are part of the headwaters of the Los Angeles River .
The Santa Monica Mountains NRA contains 156,671 acres ( 63,403 ha ) in the Santa Monica Mountains of the Transverse Ranges between the Pacific Ocean and inland valleys .