is this just for motorcycles and atvs, or are there areas for full size 4x4's and Jeeps?

chappie-shasta has does have 2 roads route 1 and route 2 that are definitely wide enough for full size jeeps ,4×4 travel but primarily the park caters to off highway vehicles trails are geared for motorcycles ,quads and there are some that can handle side by sides

There are areas for 4x4s and jeeps. Those trails are marked on the maps and trail heads.

There are at least a couple decent drives that our camp host Brian let us know were alright for even our extended cargo van camper. A few more options depending how adventurous you feel!