Black and white photograph of Mud Volcano, Yellowstone National Park.

Black and white photograph of the Grand Canyon of the Yellowstone River. Taken by Robert Merrill from Grand View.

Black and white photograph in portrait orientation of the Grand Canyon of the Yellowstone River, Yellowstone National Park. Taken by Robert Merrill looking north.

Black and white photograph in portrait orientation of the Grand Canyon of the Yellowstone River, Yellowstone National Park. Taken by Robert Merrill, looking south from Inspiration Point.

Black and white photograph in portrait orientation of the Grand Canyon of the Yellowstone River, Yellowstone National Park. Taken by Robert Merrill, looking east below Grand View.

Black and white photograph in portrait orientation of the Lower Falls from Red Rock, Yellowstone National Park.

Black and white photograph of Lena Billington Merrill standing below Point Lookout, Yellowstone National Park.

Black and white photograph of Lower Falls, Yellowstone National Park. Taken by Robert Merrill, looking down from brink.

Black and white photograph of the Norris Geyser Basin, Yellowstone National Park. Taken by Robert Merrill, looking northeast. A man can be seen standing at the left of the image, and a horse-drawn carriage appears to be driving up the road from the…

Black and white photograph of the Norris Geyser Basin, Yellowstone National Park. Taken by Robert Merrill, looking north. Several figures can be seen at a long distance. Water damage is visible on the image, which was scanned from the negative.

Black and white photograph of a woman named Rebecca looking at a chipmunk, Yellowstone National Park. Water damage is visible on the image, which was scanned from the negative.

Black and white photograph of Obsidian Cliff, Yellowstone National Park. Water damage is visible on the image, which was scanned from the negative.