Reddit reviews Afoot and Afield: Orange County: A Comprehensive Hiking Guide

The loop we did is marked on your topo as the navy blue line to "Jct 1100", then the purple line up the ridge to Four Corners, then the green line back to Bluewater and then San Mateo Creek. We didn't go any further southwest down San Mateo Creek than the junction with Bluewater Creek, so I can't tell you about campsites there. I have heard (from Jerry Schad's guide) that there are some good places to camp near "Picnic Rock" a couple miles down the creek from the Bluewater junction. I don't know any more specifics than that.

Some of Jerry Schad's hike guides were published in the San Diego Reader, so you can find them for free on the web but I highly recommend the books for SD and Orange county, they are fantastic.

All the creeks were flowing great; there was tons of water. Deep enough to swim in some places. That was a month ago, so it's wise to check with the rangers first just to be safe, but I bet there will be plenty of water in the creeks. The first water we saw after we got on the ridge was where the green line crosses the marked creek about 1.5 miles SSW of Four Corners (33.5745, -117.4429). That was flowing pretty well but kind of hard to access in places. I didn't look too hard for the springs in Oak Flats, since we were heading right back down to the creeks, so I can't tell you if there is water up there or not.

EDIT: Oh crap Hikin' Jim! Your blog post was one of the big reasons why I decided to do this trip! You probably already know 90% of what I just told you, sorry for being pedantic.