You need an Adventure Pass ($5/day) or a National Park Pass to park. You can get an Adventure Pass at Big 5, etc. You can't get them at Rowher. Most of the time you won't see Rangers checking, but you'd be taking a chance. You don't need a pass to drive the trails, just is you leave the vehicle parked.
Ive been going to rowher flats atleast 1 day a week for the last 6 months or so. I park my truck at the first staging area off load my bike and ride all day. Ive not one time seen a ranger or gotten a ticket or even bought a pass for that matter. To each there own though just giving my experience. Good luck , have fun and enjoy.
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