I wish I had an answer for you, I'm in the SD area. If it was me I'd start scouring Google Maps, looking at nearby forest roads, and also go pickup one of the Socal Trail guidebooks for the area. I know there's got to be a bunch of stuff up there.
Maybe you could download Alltrails app. Found this out recently from another site. This app would help you find the trail near you in the area. I went through the app and saw several trails that I can go on. It has 3 levels of trails of easy, moderate and hard. I'm sure you'll find many of them you would like to go on.