Down in Ocotillo Wells, CA, there is a neat little offroad excursion to explore called Sandstone Canyon. From the San Fernando Valley, you start by heading down the I-5 south. Take the 210 East and then the 10 East. Around Indio, keep right and take the 86 South. Follow the signs for Brawley/El Centro/865 Expressway. Turn right onto CA-78 and follow the signs for Ocotillo Wells. When you get to Split Mountain Road, make a left.
The trailhead for Sandstone Canyon is at:
Be careful if you are going after a rainfall as flash floods are common in the area.