Submitted by The_Albino on Thu, 2014-01-23 19:11 Groups audience South Coast - 923 Vote Up Down +6 + 0409111101a.jpg Upper Santa Margarita River The upper Santa Margarita River basin in northern San Diego county. The Santa Margarita estuary is located on Marine Corp Base Camp Pendleton and is likely the most intact steelhead habitat in southern California. The South Coast chapter of Trout Unlimited is working to enhance steelhead habitat throughout the Santa Margarita watershed.