That's the Wave Boulder, near the Barker Dam parking lot. It's now off limits to climbing as part of an area where petroglyphs are located.
We went out there this weekend and looked at the Wave Boulder. On the east side is sign that shows that climbing is off limits, however, just to the left and underneath the north side is a sign that just says no climbing on the north side of the boulder.
I was a bit confused. Clearly, they don't want you on the north face, but I wasn't sure about the south side. I decided not to ascend the south face, and left for something else, but I would have liked to have tried it.