Welcome to STR!!
El Prieto is a really great singletrack, i was very impressed with it.
I'm in Ontario, but ride all over. we did a couple of rides up in the angeles natinal forest this year already, and plan to do more once it gets warmer. the Santa Monica mountains are a lot of fun, and i mainly stick to the Topanga Canyon / Will Rogers State Park area. Turnbull Canyon in Whittier is not far from you also. i plan a lot of rides there, my next ride there is going to be a slower paced ride for some beginners, but you're welcome to join us.
so keep an eye out, if you're not afraid to drive for a bit in order to get a great ride in, you'll have fun with STR.