Near this location, the Yellowstone Trail originated from a grassroots movement of local volunteers and became the first transcontinental automobile highway across the northern tier of the United States. In 1912, when adequate all-weather roads were rare, the idea grew among South Dakotans through J.W. Parmley, who wanted a good road from Ipswich to Aberdeen, and Lemmon hosted the first Yellowstone Trail Association meeting. Thirteen elected directors, including three from Hettinger, mapped a route in both directions, promoted it as the "Shortest Route to Yellowstone Park," and encouraged citizens to build their own sections. The road soon stretched 3,700 miles from Plymouth Rock to Puget Sound, and much of its western route later became U.S. Highway 12. Adams County celebrated its first Trail Day on May 22, 1914, as volunteers worked with picks, shovels, horses, discs, harrows, and improvised drags, while six sandstone obelisks from south of White Butte still mark the trail within 13 miles of this site. Across this valley, hundreds of tepee rings once marked camps used for centuries by nomadic buffalo-hunting families from many Indian tribes at Hiddenwood, including more than 2,000 Teton Lakota during the Great Buffalo Hunt of 1882. Generally older than 200 years and sometimes 1,000 years or more, the rings show how stones anchored large buffalo-hide tepees and preserve traces of camp life on the region's grazing lands. Petrified wood is also widespread in this part of western North and South Dakota, including large pieces from hills 10 miles north. Most of it dates from the Paleocene era 55 to 67 million years ago, when swamps and forested floodplains covered the area, though some comes from the older Hell Creek Formation of the Cretaceous period 145 million years ago, when Tyrannosaurus Rex and other dinosaurs lived here. As buried trees were preserved in oxygen-poor mud or sand, mineralized groundwater gradually replaced the wood's structure with silica or quartz, leaving stone that retained grain, rings, and knots.