Yes that's the area. The whole plateau area North of Diffwys/Foel Penolau. The pictures below were from some exploring I did in Spring 2009 whilst house-sitting a cottage in the Rhinogs for friends, I wasn't much of a boulderer at the time but did a bunch of easier lines on the walls in the photo and further around from there. There looked to be lots more potential and I remember an impressive jutting prow on one boulder. Can't promise anyone they won't hike for miles and find a load of total shite though, like I said I wasn't much of a boulderer at the time so my perspective might have been out.
I parked at Cefn Clawdd and walked up the old pony track and then over Foel Penolau (about 40 mins) but a better option would probably be parking at gr684368 and taking the path due West up to the plateau.
the locals