u may want to hook up w/these guys!! http://socaltrailriders.org/forum/showthread.php?p=16176#post16176
I don't think you really want to go all the way to JPL, you might just go to Switzers as the route from Switzers on down is not very rideable and the trail is difficult to find unless you've done it recently a few times. There are boulder fields now that weren't there before and if you don't mind hiking a lot then it might be okay. The Strawberry ride will be doing Red Box to Switzers after doing Strawberry.