Columnar jointed lava flows from 1.3 million years ago at Narrows o...

The two distinct, columnar-jointed, lava flows seen here in the Narrows of the Grand Canyon of the Yellowstone River erupted about 1.3 million years ago at about the time of the second caldera-forming rhyolitic ash-flow eruption, west of Yellowstone National Park. Thick layers of stream-deposited gravels lie beneath and between the two lava flows visible in this photo. The cliffs eroded into pinnacles below the lower basalt are older volcanic rocks of the Absorka volcanic field.