The rock formations are called Hoodoos, which is the actual geological term for a pillar of rock, usually in a fantastic shape. In this case, the rock at the very top of the hoodoo is harder than the rock below it. Erosion has eaten away at the sides of the formation, but the hoodoo itself is protected by the stronger cap at the top.

Eventually, all of the hoodoos will be worn away, so it has become our mission to photograph them all before they go. (And photograph them all many, many times.)