I stopped at the park office this afternoon and Ranger Brian was there. He was OK with the idea that the trails could be open during freeze conditions.
Gary and I had a good ride through Over Lode/Chert Dip. The trail is slow because the trail was saturated when it froze and the top layer of mud froze. Frozen mud = dirt/ice emulsion. The ice begins to sublime away resulting in a dirt mousse.
http://en.wikipedia.org/wiki/MousseIt's kind of like riding in sand, but with more crunchiness. Good traction, but takes extra power to pedal through.
BEWARE THE DIRT MOUSSE! (There's no real problem, I just like the ominous sound.)
Walt