White Rock's hardest to access, least developed crag. Potential for some hard sport and trad routes on overhanging basalt. I recall the rock quality (it's been more than a decade) as excellent.
I can't tell you much about the routes here, because Luke and I only visited a couple of times. I toproped some stuff, but I don't remember much about it. If you're willing to hike for 45 minutes to an hour, go check it out.
Approach as for the Big Enchilada, then hike downhill and south into the huge drainage. Follow this all the way to the Rio Grande, and you'll pop out right at the crag (if you don't see it, just walk up or downriver for a few hundred feet and you'll find it). Approach hike is about 45 minutes (from the Big Enchilada), return hike is quite a bit harder.
In 1991/1992 a group of us (Mike Lyons, Jason Cox, Phil Hoffer, Jon Butler, Carlo Torres and I) made several overnight trips down to the River Crag to explore and climb. Because we didn't have a power drill we only picked off a few of the obvious crack routes in the area, except for Carlo, who painfully hand drilled one sport route, that's probably 5.11-, in the center of the wall on perfect bullet hard polished rock. Jason Cox and I later returned with Cameron Burns for another couple routes. It would probably be a great spot if it was closer but it was just too far to walk...