I am searching for about the same thing. I live in Westlake Village, which is north of the Santa Monica Mountains. At this point I am learning to use my astrophotography gear in my back yard. But, as soon as daylight savings time starts, and we get a little warmer weather, I will seek out alternatives. I have the same concerns about safety that you seem to have. I have a few options on my list to check out. One is Malibu Creek State Park on Las Virgenes road. They charge an access fee, but I have a free pass to all state parks. I am thinking of renting a camp site, but not camping, just using it until I am done, pack up and go home. The light pollution there, according to the published information, is far better than at my home. I have also camped at Mugu state park, further up the PCH. They have campsites and day use similar to Malibu Creek. Not sure how good the seeing conditions might be close to the ocean. A little further down the coast, there is a parking lot next to Point Mugu Naval Air Station but public access to the beach a short distance away. It is not as safe as a state park, but being next to a military base calms my nerves. The address is 6859 Arnold Road Oxnard, CA 93033. Then a little farther down the coast is Point Hueneme Pier, which is open all night. Next to the pear is public parking. Have not tried it, but it is on my list. Also there are several local parks near my home, in good neighborhoods which I want to try out. One is Sapwi Trails Community Park, on the intersection of Westlake Blvd and Los Arboles. An extremely safe neighborhood. There is a left turn into the park from Westlake Blvd, which leads to a radio controlled glider launching pad built by the City. There is a large parking lot next to that pad. It is empty at nigh. But it is surrounded by a neighborhood of homes. Not sure how much light pollution is there, but it is easy to get to for me, good parking, public restrooms, and as safe as can be. Let me know what you find out. If I test any of these sites I will post what happened.