Despite its name, Nine Mile Canyon in eastern Utah runs for about 40 miles through Carbon and Duchesne counties, cutting a natural corridor through the Book Cliffs roughly 125 miles from Salt Lake City. Nobody is entirely sure where the name came from. One theory is that the explorer John Wesley Powell used a nine-mile measurement called a transect when he mapped the area in the 1870s, though even that is mostly speculation.

What is not in dispute is what covers the canyon walls. With over 1,000 rock art sites and more than 10,000 individual images, Nine Mile Canyon is often called the world's longest art gallery, and the title is well earned. Most of the petroglyphs and pictographs were made by the Fremont people, who lived in the canyon from roughly 950 to 1250 C.E. The Fremont were not purely nomadic. They built semi-permanent villages, farmed corn and squash along the canyon floor, and engineered small irrigation systems fed by Nine Mile Creek. Their rock art ranges from hunting scenes and animal figures to abstract designs that archaeologists are still working to understand. Later, the Ute people added their own images to the walls, many of them depicting hunters on horseback and dating to the 1800s.

The canyon's history did not stop with its ancient inhabitants. In 1886, the Buffalo Soldiers of the 9th Cavalry Regiment built a road through the canyon connecting Fort Duchesne to the railroad in Price, and Nine Mile became the main route for freight, mail, and stagecoach traffic into the Uinta Basin. A small town called Harper grew up around one of the stagecoach stops, with a hotel, store, and school. It is a ghost town now, its remains scattered along the canyon road.

Today, the canyon is a designated Scenic Back Country Byway, and the road through it was finally paved in 2014, a project that came partly out of concern that traffic-generated dust was settling on the petroglyphs and slowly wearing them away. More than 220 archaeological sites in the canyon are listed on the National Register of Historic Places, and the work of documenting and protecting them is ongoing.