Hey, thanks for all the responses.
I think the reason for all the mud near Graniteville was there was melting patches of snow on the sides that were keeping the roadway pretty wet. I almost lost the front end at 20 mph and I had the rear wheel spin out twice on short hills and almost lost it so I turned around.
I wasn't aware of the closure at the park entrance. I went the Briceburg way this spring, heading down the switchbacks. I saw the fork to old Yosemite Road, right after Bower Cave, and wanted to try it. But if it's a turn around, I won't even bother.
I'll be riding a KLR so plating isn't a problem, but there's an upward limit of how rough a road I can handle on such a big bike.