The eastern gateway to the Hills is Rapid City, a metropolis of thirty thousand people which lies on the level prairie just to the east of the final ring of foothills. Founded, like Spearfish, not as a mining center but to serve the near-by gold regions, Rapid City has developed a maze of industrial and commercial enterprises. Shipping, of course, has been a basic form of commerce from the earliest days, with the two most heavily traveled trails into the Black Hills, that from Fort Pierre and that from Sidney, Nebraska, on the Union Pacific, entering the gold area at Rapid City. Lumbering, manufacture, banking, and livestock quickly became prominent as the gold fever subsided and the more permanent settlers began coming into the region to take up the rich cattle and farming lands in western South Dakota. A final guarantee that Rapid City will continue to flourish may be seen in the selection by the Air Force of the high, level prairie land just ten miles to the east of the city as the nation’s major mid-continent bomber base. Rapid City is served by U.S. Highway 14-16, and South Dakota state highways 40 and 79. Two railroads and a major airline assist in handling the heavy summer tourist travel, and from Rapid City practically every point of interest in the Black Hills can be reached by car within three hours. CHAPTER TWO The Formation of the Black Hills One of the most rewarding features of a visit to the Black Hills is the opportunity for the average individual, who has no technical training, to see with his own eyes a museum of the earth’s ages and a living sample of practically every one of the many aeons of the planet’s history. The Hills, which is to say the rock substances of the region, are older by hundreds of millions of years than the stone out-juttings of the Rocky Mountains. Layer after layer of slates and schists from the very foundations of this globe lie visibly exposed as the end result of a doming of the region, a vast blistering, as it were, which raised the entire structure, layer upon layer, several thousand feet in the air. Following this doming process, a vigorous program of erosion commenced. Stratum by stratum the winds and rains cut across this huge blister in a horizontal plane, eventually laying the core open at the height above sea level at which we find the Black Hills today. From that core, extending in every direction in the general form of a circle, the various strata which once lay so smoothly one upon another have been laid open as one might slice off the top of an orange. [Illustration: The Doming of the Black Hills Rock Strata being shifted into a dome at the time of the great continental uplift. The forces of erosion—wind and water—have levelled the dome and opened the seams to view.]