Would that be Montana or up that way? Sorry not as familiar with the northern part of the country, but would love to go....but in like July.
Western South Dakota, about 90 miles from the eastern-most Montana line. If you want to visit Mt. Rushmore, come in June, when it is warm but not over 100 and rife with severe thunderstorms like July/August. But if you are a biker, August is the month for the world's biggest motorcycle rally in Sturgis (about 75 miles from my place).
I also have lived in Oregon, Texas, Illinois, England, Italy, Arizona, Montana and have driven through 30 of our states, so you will often hear me BS about them as if it was only yesterday... the older you get, the fresher the old memories and yesterday mysteriously disappears.