South Dakota and Colorado later this month

When you go up Pikes Peak it could snow and it will be very cold on top. Bring appropriate clothes.
There are great crystals to be found on Pikes peak when you get into the fields above timberline. When the grass begins to disappear, get out and walk 100 yards and usually you will find some pretty nice smokies or clear quartz crystals.
If your really into the tourist part, go up the cog railway. Too slow for me and I can't get out and find stuff.
The trail, Barr trail right next to the Cog is a decent trail if you are into hiking all the way to the top. You can do it in a day.
The weather swings in Colorado can be drastic, It's 100 today in the eastern plains and the western slope but where I'm at in the mountains it was 70 today. Night times are in the 40s/50s still in most places.
Garden of the gods can be fun. When you find the balanced rock, there is a small dirt road called Rampart range road not even 1/8 mile from the balanced rock, go up that about another 1/8 mile and stop and get out on the giant flat rocks. They are an awesome hike that I have taken my family to many times.
Otherwise Garden OTG has a ton of trails that are well traveled and several parking spots.
As a Coloradoan, Pikes Peak is a little bitty dinky thing.
If you really want the experience, come up to Salida and rent a few jeeps, follow me in my jeep an I'll take yal up Mount Antero. That is the real way to tour a mountain. And you can find Aquamarine crystals on Antero.

Feel free to message me if ya need any suggestions for your time in Colorado.