In case anyone needs this information in the future, the route through San Bernardino is awesome! The shoulder isn't always very big, but the road is extremely twisty, so cars generally go pretty slow. It is a serious climb to Onyx Summit, 8,443 ft from 3,000 at the beginning of the national forest and 1,500 or so from San Bernardino, but completely worth it. I did the climb in one very long day and stopped a lot, but it can definitely be done in much less time. From Onyx, it is an easy, beautiful ride down to Big Bear and then on highway 18 to highway 247 (old woman springs) to Yucca Valley. Highway 18 again doesn't have much of a shoulder, but it is extremely twisty and gorgeous. It shoots you right into the desert and then there is a straight, slightly downhill for most of the way, ride into Yucca Valley. The camping within San Bernardino National Forest is in abundance, but once you leave, the desert is very barren and there isn't cover. The only issue with this route is that it leaves you in Joshua Tree National Park and if you are heading East, the only way to go is on route 62 which is an awful road to bike on. I haven't left yet, but I am dreading leaving the park because 62 is very unpleasant and unsafe, fast traffic, no shoulder, flat, and ugly.