Antelope Canyon (Upper and Lower): Upper and Lower Antelope Canyon seem to be the most-visited (and most-photographed!) slot canyons. It is challenging to get a 'unique' image, and they are very busy locations! Unlike my other set from Canyon X, the challenge with both Upper and Lower Antelope canyon is to capture an image without the hundreds of other tourists getting in the way. This is true "combat photography". These slot canyons are formed by the erosion of the Navajo Sandstone primarily during times of flash flooding where the rain is channeled into the canyons and the action of the sand and rocks in the wash erodes the slot/corridor giving it the smooth shapes. If you are looking to access these canyons, I would highly recommend contacting Overland Canyon Tours who have photographic tours that allow the use of tripods.