Originally Posted by
TRRed
Ditto on point 1. Traffic may and slow and accomodations hard to find at that time of year.
You'll likely also be driving by Glacier National Park (in Montana, just south of the Canadian border, where you can get the same pass before hand and visit another beautiful park.
Indeed another amazing place. The road across it the park opens in june sometime; when we were there a few years ago in early June it was still closed.
Note that each park sells park specific passes (I think the yellowstone and grand teton passes were together) and annual US passes. The senior citizen and disabled visitor discount passes are for US citizens and permanent residents only. If you chose to visit Glacier and Yellowstone, you've almost bought an annual pass worth or one week passes..