An enormous collection of weirdly-shaped rock pinnacles, remnants of a huge volcanic eruption about 25 million years ago, cover the higher regions of the park.
In a remote and wild area in Southern Arizona, you can visit the largest concentration of organ pipe cactus.
It preserves the prehistoric ruins of an ancient Hohokam community.
The National Monument actually comprises three canyons, with walls rising steeply for about a thousand feet.
