The Beartooth Plateau contains some of the oldest exposed rocks on Earth and provides a unique window into the history of the planet. About 55 million years ago, this massive block of metamorphic basement rock pushed upward nearly two miles along steep faults extending deep into the Earth. Its exposed coarse-grained gray and pink granites, gneisses, and schists formed about 3.3 billion years ago when older sedimentary and volcanic rocks were heated and recrystallized deep in the Earth at extremely high temperatures. These are the oldest exposed rocks in Montana and among the oldest on Earth. On the plateau’s northern flank, the Stillwater Complex is one of the world’s major sources of chromite, platinum, and palladium. During the ice ages about 100,000 years ago, enough snow accumulated for glaciers to form and cover most of the plateau to depths of several thousand feet. As they spread, the glaciers wore down the upper surface, leaving rounded rock outcrops along with hundreds of lakes, ponds, and depressions, and they flowed down old stream valleys, deepening and straightening them into valleys with vertical canyon walls and jagged peaks. The summit of the plateau is alpine tundra. Native Americans used trails across these mountains since prehistory, but not until the 20th century did many seek a permanent route over the mountains from Red Lodge to Yellowstone National Park. After the Red Lodge coal mines closed, Red Lodge businessmen lobbied Montana’s congressional delegation for a road between their community and the park. In 1931, President Herbert Hoover signed the Park Approach Act into law, funding scenic routes to national parks through federally owned land. Construction of the 2.5 million dollar project began in 1932, and about 100 workers employed by five companies blasted their way up the side of the 11,000-foot plateau. The workmen named many road features still used today, including Lunch Meadow, Mae West Curve, and High Lonesome Ridge. The road officially opened on June 14, 1936, and it still looks much as it did then while giving motorists access to rare high-elevation alpine scenery on a North American highway.