I, too, observed some incredibly stupid behavior at a national park in Colorado (this being the Great Sand Dunes). I climbed up one of the high dunes for some photos and turned westward to see some nasty storm clouds fast approaching. I see some tourists well off in the direction of the storms on the dunes (and there’s no way they can’t see what’s approaching) and they’re continuing to walk westward. I couldn’t warn them as they were too far off, so I practically ran down the dunes east back towards the car before the storm hit. To be caught out there in the middle of the dunes with a thunderstorm and lightning with no place to take refuge... epic-level idiocy.
Yes, they could have been victims of the famous flash floods, or struck by lightning. The cool thing about Colorado is that you can see your afternoon thunderstorm developing all day long in the distance, gradually drawing closer to you. So you can't say you weren't warned, if you are weather-wise.
And let's not forget the few tourists that get fried from cloud to ground lightning every year in the keyhole on Longs Peak in Rocky Mt. National Park. Lightning can be drawn to you by your keys, your carabiners, etc. I really feel for the rock climbers I see who are really far up when one of the sudden mountain storms strikes.
I remember hiking up the Watchman Trail in Zion National Park (beautiful!!) one summer and nearly getting to the top. I glanced up and saw that right over the mountain was a big sudden storm. My friend and I RAN down that mountain like mountain goats. Funny how it took so much less time than laboriously making our way UP that mountain. We ran as fast as humanly possible and just made it to the ranger station before the deluge struck, big bolts of lightning and all. Whew!