Wikipedia says that Boulder, MT, is at almost 5,000 feet of elevation and that it is just east of the Continental Divide. You must have gone over some pretty high mountain passes on this route. Wonder what the highest elevation was that you hit?
I went skiing in Colorado one time many years ago. Denver is the "mile high city" so 5,200 feet elevation. When you get through the Eisenhower Tunnel--which is also on the Continental Divide-- the valley floor is around 9,000 feet and the peaks go up to around 14,000 feet. Lots of people get altitude sickness at those heights. I had headaches and fatigue the first few days. Very weird for a guy who grew up in Ontario (500 to 1,000 feet elevation)!
Craig