Two ledges of basalt spectacularly exposed in the east wall of the Grand Canyon of the Yellowstone at The Narrows near Tower Falls. Yellowstone National Park, Wyoming. 1970.

Album caption and index card: Two ledges of basalt spectacularly exposed in the east wall of the Grand Canyon of the Yellowstone at The Narrows near Tower Falls. The light-colored rocks between the basalt flows are ancient stream gravels deposited about 1.5 million years ago, when the channel of the Yellowstone River was farther east and not as deep as it is today. The hill is capped by lake sediments, sand, and gravel deposited when the Yellowstone River was blocked by a glacial dam farther downstream (to the left). The brown rocks at the base of the cliff are Absaroka andesite breccias. Yellowstone National Park, Wyoming. 1970. Published as a portion of Figure 33 (upper photo) in U.S. Geological Survey. Bulletin 1347. 1971.