After riding down Mt Baldy Rd a few times, I would never attempt to ride up and much prefer the descent on GMR-GRR.
If I get lucky, GMR-GRR will be closed to vehicles but it is a slow descent in winter with rocks and ice along the way.
I had to turnaround once on GRR due to ice even though I was on my 29er. Had second and third thoughts that this would be a self-rescue if I went down hard and injured myself. Hypothermia would be a real concern.