+1. Also, there are a good number of light-traffic places to ride in OR and MT. Last year's Cylcle Oregon route had very little traffic most days. On Day 1 (Bly to Silver Lake) we probably saw a half dozen non-event-affiliated vehicles in nearly 80 miles of riding.
In 2011 we did a loop from/to Missoula starting at the end of June. Except getting out of and back into Missoula, there was very little traffic. Even Butte wasn't bad. What helped is that we did about 60 miles of dirt roads.