I gotta get you a USFS key, Buzz. I poach closed campgrounds all the time. I've never been questioned, but then that may be because I made up a magnetic sign for my truck that says American Land and Leisure. (The folks who contract the campground management for the USFS in these parts.)
Thanks for the photos. I enjoy camping in that area regularly. BTW, there's a campground just north of Sierra City called Wild Plum. It's back in a ways. If the gate is closed for the season, there's a turn out right on the water at the fork in the road where the bridge is gated leading into a private community. Also, there's a parking area for the PCT that is good for a night of free camping too and the river is right there. Here is a photo of me and a bud motorcycle camping there is past September;