There are twelve sites on top of the mesa, no bookings are taken, and an entire district sits inside about ten miles of road. That is the trade at Willow Flat: you gamble on a spot, and if you win you are already on the rim when the light turns instead of driving up from Moab in the dark. Have a fallback in mind on the way up, because a full campground here means a long drive back down.
Tip: Mesa Arch sunrise is five minutes away. That's the whole pitch.
Out the tent door: Mesa Arch (Hike, 1 mi) · Upheaval Dome Overlook (Hike, 4 mi) · Grand View Point (Hike, 5 mi) · Dead Horse Rim Loop (Hike, 11 mi)