The Sturgis South Dakota motorcycle rally is August 7-16. Things start getting crowded on the roads around that area 2 weeks before and about a week after the rally.
It is not just motorcycles. There are many RV's and other vehicles going there and there will be crowds around Rushmore, Deadwood, Devil's Tower, Badlands, etc.
We usually got in to that area about 7-10 days after the rally and found plenty of room at the RV parks and no big crowds at the various sights. In fact we found some great prices at the downtown Sturgis RV park(Closes the end of September), which was a good place for us to use as a parking place and use the toad to travel to Deadwood, Rushmore, Devil's Tower, Badlands, Needles, etc.
