The highway mounts the spine of an esker, and follows it for a few miles—veering and curving with undulating coils of a landform deposited eons ago inside the bowels of a thousand-foot-deep glacier. It’s serpentine and a bit weird, so stylized and consistent that you might wonder if it could be the artifact of a human civilization. Geologists tell us that these ridges of silt, sand, gravel and cobble are the beds of subnivean streams that once flowed deep within glaciers, where the material was deposited between walls of ice. Once the glacier melts away, these streambed foundations remain as elongated mounds. While this esker is especially dramatic, be sure to look for them elsewhere along the highway, says the BLM Recreation Guide. They are some of North America's best examples of this type of glacial feature.