The park is named for the "Medicine Rocks," a series of sandstone pillars similar to hoodoos some 60 to 80 feet (18 to 24 m) high with eerie undulations, holes, and tunnels in them.

[10] Medicine Rocks is part of the Fort Union Formation, a geologic unit containing coal, sandstone, and shale in Montana, Wyoming, and other adjacent states.

[11] About 61 million years ago, near the start of the Paleocene Epoch and during the late Zuñi sequence, a freshwater river crossed what is now eastern Montana, flowing southeast into a prehistoric sea whose boundary was near far northwestern South Dakota (possibly the remains of the Western Interior Seaway).

[18] Wind, dirt, sand, and rain carved the sandstone over the millennia, so that now the structures exhibit numerous arches, caves, columns, holes, pillars, and flat-topped towers.

[6] According to Ed Belt, retired professor of geology at Amherst College, the Medicine Rocks sandstone is almost unique.

[15] Aside from the other-worldly nature of the rock formations, Native Americans were attracted to the site because of the many medicinal plants which grew there and the fossil seashells which could be gathered for decorations.

[12][19] The Cheyenne stopped at Medicine Rocks on their way from the Yellowstone River Valley to the Black Hills each summer and early fall.

[12] Sometime prior to the mid-17th century, the Hidatsa leader No-Vitals led a large number of Hidatsa out of what is now western North Dakota west into the Yellowstone River valley of south-central Montana, where the new tribe (the Crow) lived on the plains, by the river, and in the nearby Big Horn, Pryor, and Wolf Mountains.

[12] In the 1910s and 1920s, Medicine Rocks was a favorite picnic spot for local people, who often drove to the site every Sunday for feasting, entertainment, and conversation.

Twelve primitive campsites are available at Medicine Rocks,[15] as well as tables, fire rings, vault toilets, and cold spring water from a hand pump.