Best Off-road trails & "practice" areas around Los Angeles

I'm an experienced rider but new to the GS world and am looking to "workout" with my bike. I'm near the coast in Los Angeles and seeking some advice for the best places to go to work on off-road skills (with my friends or on my own, not a Skills Camp). Thanks for the help!
2015 r1200gsa

Off pavement opportunities near LA?

They have gone the way of the Dodo bird.
I believe Riverside BMW has an active group of GS riders.
The few places about an hours reach from LA that I know about are closed because of fire or flood damage.
Oh, and everything else has been developed. (They HAVE paved paradise, and it IS a parking lot)
I will not be specific online.
Imagine LA traffic on all the trails!
Summertime head North and stay close to the coast, Wintertime head East and South, stay on secondary roads and once your in the boonies take the first unpaved road you see.
If that doesn't work, try the next one.


Here's the advice; #1. Get lost!
#2. Don't pay any attention to anything an AirHead advises.

Anybody else?

Okay, there are now many designated OHV areas in California.
A few closest to LA are Wildomar, (Ortega Hwy. near Lake Elsinore) Hungry Valley, (Gorman) Rowher Flats, (Agua Dulce)
A little farther out there's Johnson Valley, (Lucern Valley) El Mirage Dry Lake, and Ballinger Canyon, (New Cuyama)
My knowledge of these areas except Ballinger Canyon, predate the OHV designations, so I know little about what they are like now other than there is little if any pavement.

It's been 3 years since I have been there, but the area just North of Big Bear Lake (it's not designated OHV) has some forest service roads that are easily passable, and some that a goat would have a hard time on.

When it cools off California City, Randsburg, and Wagon Wheel are excellent.
Years ago when returning home from Death Valley, I stopped in Randsburg to take a break.
There were hundreds of motorcycles in town, I was on the only street legal bike that I could see!