I wonder most about the bits in Idaho and Oregon - that goes through some pretty mountainous areas, doesn't it?
Yes it's hilly, and it's high... it could get snow anytime, but compared to real mountains, I don't remember it being bad. And the route through the Columbia Gorge to Portland like it does is the easiest way across the Cascades, you follow the river so it's not steep or particularly winding ;~D.