The Lower Falls of the Yellowstone River in Yellowstone National Park, photographed on September 2, 2006. #

The lower basin of Mammoth Hot Springs in Yellowstone National Park in the 1870s. #

A brave flapper feeds a bear along the shores of Yellowstone Lake, circa 1925. #

Tourists drive their car on a dirt road along the Yellowstone River in the early days of Yellowstone National Park. #

Visitors stand near geysers in Yellowstone Park, Wyoming, in this undated photograph. #

In near freezing weather, U.S. President Franklin D. Roosevelt stops to admire the Lower Falls in Yellowstone Canyon, on September 26, 1937. #

A black bear walks among visitors to Yellowstone National Park in this photo, circa 1960. #

A coyote walks in Yellowstone National Park, Wyoming, on August 11, 2011. #

Canary Spring terraces, part of Yellowstone's Mammoth Hot Springs, photographed on December 2, 2016. #

A bison group in the road, near Frying Pan Spring, on February 24, 2017. #

An erupting Old Faithful geyser and the Milky Way crisscross on a clear summer night on June 24, 2017. #

A bison jam in Hayden Valley on August 25, 2017. #

The setting moon and an elk, photographed in Mammoth Hot Springs in March of 2015. #

A lone coyote on Yellowstone Lake on February 15, 2017. #

Tourists watch Old Faithful, which erupts on average every 90 minutes, in Yellowstone National Park on June 1, 2011. #

A trumpeter swan takes off from a pond on May 5, 2017. #

A bison group on the move at sunrise in Lamar Valley on June 30, 2017. #

A black bear runs across a bridge spanning the Yellowstone River near the Lamar Valley in Yellowstone National Park on June 24, 2011. #

Alder Fire in Yellowstone National Park, photographed from above, on August 19, 2013. #

A male pronghorn, photographed on Blacktail Deer Plateau on May 14, 2017. #

Looking down from the brink of the Yellowstone River's Lower Falls, on August 25, 2017. #

A marten in a tree, photographed on February 12, 2017. #

A bison calf following a cow on Little America Flat, photographed in May of 2005. #

Hikers ascend the north side of Electric Peak on July 15, 2017. #

It may appear frozen at first glance, but the Lower Falls in the Grand Canyon of the Yellowstone River flows among the snow and ice on February 8, 2016. #

A white-tailed deer in velvet, photographed on July 12, 2017. #

An aerial view of Upper Geyser Basin, photographed in June of 2006. #

A grizzly bear near Frying Pan Spring, Yellowstone National Park, photographed on May 19, 2017. #