It was easy to see why the park is known as Craters Of The Moon. In the background is one of the cinder cones.

"Craters of the Moon sits astride the "Great Rift." Eight times in the past 15,000 years lava poured from cracks which opened along this weak spot in the earth's crust. Expanding gases in the lava ejected bubbly rocks hundreds of feet into the air. In some cases these cinders showered the ground to form cones. Less explosive lava flowed in sheets and rivers. The lava moving beneath the congealing crust sometimes tugged the surface into folds resembling coils of rope. This type of lava is called pahoehoe, which means "ropy" in Hawaiian. Cooler, thicker aa lava—with a consistency much like peanut butter—inched along, twisting and shattering into tumbled masses of jagged rocks. Aa is a Hawaiian word loosely translated as "rough on the feet," a description worth keeping in mind as you select your hiking shoes."