Today I decided to see how much snow there was up in the San Gabriel Mountains by driving the Santa Clara Divide Road (3N17) which stretches 31 miles along the ridge lines from Sand Canyon road to Angeles Forest Highway. I only made it about 2/3 the way.
I turned around when the snow was so deep that the tracks ended. Previous drivers had stopped and turned around, leaving clean snow ahead probably the entire way past Mt. Gleason to the pavement. I turned around there also. It was already dangerous enough. The road was seriously rutted - very deeply in places. But those ruts were generally easy to handle because of the freezing temps.
It was in the 20's and the snow and ruts were frozen solid. The greatest hazard was when the ruts would take you dangerously close to large boulders. Wherever I could, I stayed out of the ruts and drove atop the frozen snow. As the road climbed higher in elevation (passing 6000 ft) the snow was deeper and the ruts so deep that I was scraping my belly skid plates across the frozen ridges between the ruts. Here's a Google Map centered on the place where I turned back.
Even though I just got my new tires mounted, I was risking getting very stuck all alone up there in the freezing cold. Better safe and warm than stuck and freezing.
As I returned, the sun had melted some of the ice and snow at lower elevations, so it was just muddy enough to make the rover look respectable.