It is a tall mesa hundreds of feet high, made out of a bundle of hexagonal and pentagonal columns of rock. Native Americans believed that it was carved by the claws of a giant bear which was trying to attack a group of warriors who took refuge on top of this steep-sided hill.
Geologists have a different explanation, however.
When lava is erupted by a volcano, the lava at the very top will cool first, forming a hard crust which insulates the deeper lava. This interior lava will then take much longer to cool and harden into rock. Just like most materials, rock will shrink slightly as it cools. Therefore as the lava cools, it has to shrink to a slightly smaller size. In order to accommodate this, the rock will develop a series of cracks which show the amount of extra space produced by the shrinking.