I grew up out there and rode the area a lot back in the day. As mentioned, the trail from Crafton Hills College is worth riding, works pretty well as an out and back up to the top. Fireroad with lots of switchbacks and a few offshoots, a couple ridgelines to explore. I always had the most fun out in Loma Linda that you can access from Hilda Crooks park, or whatever it's called. From big drainage basin next to the park, it's pretty easy to figure out to go, just take the main fireroad and take your pick of any trails off the side. Stay on the main fireroad and as it deteriorates you'll get to the old "Jedi" trail (anyone know what kind of shape that is in?). Quite a few ridgelines and fast stuff out there. Sometimes you can find some creative lines or just blaze down some steep stuff. You can explore those trails for quite a while heading pretty much West once you get up to the top. An old SOB hill called "Mother." Lots of up and downs, but some cool flowy lines.
If anyone rides that area much, I'd love to hear how things are out there and if those Loma Linda trails are still getting much use. I'm in San Diego now and always debate whether to bring a bike when visiting my folks out there. Had a lot of fun riding those trails growing up getting into mountain biking. Always fun post ride to pedal as fast as you can at the big grass slope at Hilda Crooks park and bunny hop like crazy and try to air down the whole thing followed by a giant grass skid. FUN