This is a wonderful area, so much diversity in one place.
Yellowstone, the best of the bunch! - Take advantage of the ranger programs and museums -- they're different throughout the park.
- Consider doing the Cowboy Cookout.
- The park is larger than you expect; do not enter without a full tank of gas. Yes, they sell gas inside the park, but it's so expensive.
- Drive defensively. People act like idiots behind the wheel and just STOP when they see wildlife by the side of the road.
- I've been twice, both times in summer, and traffic is HEAVY -- as in, 30 minute wait to get through the entrance gate. It may be better in late summer, but don't expect to zip around hither and yon.
- Be bear-aware. Yes, a bear can easily rip the door off your car to get to your food. Consider a bear-proof food container, or plan to buy your meals in the park. Each area of the park has a cafeteria and a diner (located at the back of their stores).
- Pack for all types of weather. We were in Yellowstone in early July, and I was forced to buy everyone a $50 sweatshirt because the temp dropped in to the 50s.
- Cody, WY is within driving distance from the eastern side of Yellowstone, and the rodeo is a lot of fun. The museum in Cody is also worth a trip.
- On the western side of Yellowstone is the town of West Yellowstone. Also worth a trip. Visit the Grizzly and Wolf Discovery Center (I might not have that name right). My favorite exhibit: The trash cans that've been savaged by bears. Yeah, you'll come away with a solid respect for bears.
- Similar warning: Buffalo roam free in Yellowstone. You may find yourself too near one accidentally -- walk away quickly and quietly. Every year several people are killed by buffalo, and it's usually because they got too close to these wild animals /tried to take pictures.
Grand Tetons:
- Wonderful, perhaps the most beautiful place I've ever seen.
- A bit more expensive and less populated than Yellowstone.
- Nasty little flying bugs were horrible in the lake area; don't neglect your bug spray.
- The single best hike in these parks is the hike to the top of the mountain by Jenny Lake. Take the ferry across the lake (small fee) and go all the way to the top. No bathrooms, no food service, so go prepared. Allot at least 1/2 a day. The view from the top is nothing short of breathtaking. The big granite slab at the top is a great place to enjoy a bag lunch. One of my favorite family photos ever was taken at a waterfall 2/3 of the way up.
- Consider doing the Snake River float trip. First thing in the morning or last thing in the evening is best, assuming you want to see wildlife.
- Again, ranger programs.
- Grand Tetons is within driving distance of Jackson Hole, very expensive tourist town, but nice places to eat.
There's a campground in between these two "sister parks", but I can't remember its name. When you pay for entrance into one park, you're allowed to enter the other park as well for one week.
I don't know how long you plan to be in the area, but Yellowstone and Grand Tetons could EASILY fill 1-2 weeks of travel. Personally, I'd consider making those two a trip, then plan to hit the South Dakota area on a separate journey.
Mt. Rushmore:
- When I visited as a teen, I was mesmerized by the grandeur of this place. When I returned in my 40s, it failed to elicit the same response.
- Consider going in the evening for the fireworks show.
- Entrance is free, parking is not.
- While you're in this area, you can also see the Crazy Horse Monument; it's also visible from the road. I haven't been "into" that monument.
- While you're in the area, you should visit Custer State Park in South Dakota. It rivals Yellowstone and Grand Tetons. Yes, really. Definitely take the Buffalo Safari -- expensive but worth it. So informative.
- The town of Custer is barely worth visiting. No good restaurants.
- If memory serves, two cave-related national parks are in this area. Wind Tunnel and Jewel Cave? I know I enjoyed them both.