Will Rogers state park has a cool delapitated concrete structure i've been to a couple times. Long hike but worth it.
Malibu Creek state park. What more can i say about that place.
Hwy 2, angeles crest in the winter. Can't be beat for places within an hour.

Terminal Island.

The L.A. River. A friend of mine has a fair amount of local work: http://www.johnsmithimages.com/
We have a group show here in L.A. coming up next month of urban landscapes if anyone is interested, let me know.