I climbed up on top of the easternmost butte near the amphitheater, but I couldn't find rappel anchors anywhere. There were three bolts in the rock, but all of the hardware had been removed. Can anyone confirm this?
Those are for Fire Safety and Rescue. I haven't found any rappel anchors on top of the Easternmost Butte.
There is a line of bolts on the east face of the western butte (I think its the route shown on MP), that I believe has a Rap anchor up top, but from what I've heard its a loose / chossy route and the bolts are janky so YMMV. I think most people aid up the bolts to rap down.
I did explore an unknown bolted route along the Southwest face of that same butte, I think there are two separate routes there. The climbing was ~5.6 - 5.7, the bolts looked new / clean. But I only had a single 80m Rope and about 15 quickdraws and reached the halfway point of my rope before I ever even saw the anchors so I don't know what the top-out condition is like. Also there were more than a few bolts that looked like mental ones only, i.e. they were in granite boulders that looked like they'd pull out of the hardened mud if you actually fell on it. If you want to check those out I'd recommend taking double ropes.
On the eastern Butte, there's a little chimney / gulley that you access from the east, near the southern side that you can scramble up to reach a plateau thats about halfway down from the peak that has some rap anchors set up on it, I think thats where most people rap from. I've also ran across a group out there that was just rapping directly off boulders, which is pretty sketch but hey, whatever floats your boat!