First hiked here just over ten years ago to the day. Sandstone (twice), Mugu, Boney Peak, Inspiration Point, and the Tri-Peaks.
The word has gotten out and trails are crawling with people on the weekends. The Sandstone Peak trail had (as of 1/1/18) four dog waste bags abandoned alongside it, and the number of people going up with their canines beggared belief. Not much of a "natural" experience.
Have hiked the Pt. Mugu Park trails, at the westernmost end of the Santa Monica Mtns. Have also been to the Satwiwa area, Paramount Ranch, and driven the Mulholland Hwy. Hope to hike more of this area!