There are a few interesting things that we learned though. Have you ever wanted to know the difference between a National Park and a National Monument? The difference is their objective. National Parks seek to send as many people through as they possibly can. You can show up, book a tour, and be good to go. National Monuments seek to preserve and protect the site. That means that tour groups are limited sometimes. If you show up late, you may not get a tour at all. One positive thing though is that you can reserve tickets for National Monuments a couple weeks in advance.
What this means for you: If you're planning to see Jewel Cave NM and Wind Cave NP on a trip to the Black Hills in July, you will get to see Wind Cave no matter what. If you call a few weeks ahead and reserve a tour ticket, you will get to see Jewel Cave. If you don't call ahead and show up they'll tell you that you can be on the 2 day waiting list.