El Malpais National Monument, New Mexico
You can wander around the tops of the sandstone cliffs here and find lots of interesting compositions. The cliffs look out over the black basalt plains formed by ancient lava flows. But it's the skies here that really steal the show, generating the most interesting clouds, especially on this August afternoon with plenty of thunderstorms popping up in the distance.
White Sands National Monument, New Mexico
Here in the Tularosa Basin are the largest gypsum sand dunes in the world. The basin has no outlet to the sea, so gypsum washed down from the surrounding mountains stays in the basin, forming selenite crystals.
Death Valley National Park
I love the folds in the badlands around Zabriskie Point, especially shortly after sunrise. These are the eroded sediments from a lake that disappeared 5 million years ago. You won't have this place to yourself, but you can find something of interest in almost any direction.