Never assume the maps are right, especially when driving in Winter. You have to research the route thoroughly, being prepared for any contingencies when driving in that neck of the woods.
It is very tough to navigate on foot in the snow. When I took winter survival it was no picnic.
As soon as he saw snow on the road, he shoulda backtracked. Unless you got 4wd and chains you don't want to mess with what conditions can be like there. I'm not sure I'd even try some of those areas in April, much less December.