During subsequent tens of millions of years, erosion has stripped away the softer rock layers in which these masses formed, leaving them standing as dominant landmarks. The process continues today as the Belle Fourche and Little Missouri Rivers and their tributary streams, aided by freezing, thawing, rain drops, and the other processes that break down the rock, continue to alter the face of the earth in this region. Within less than a decade after the U. S. Geological Survey party passed through the region, the first settlers were to enter the western end of the Black Hills in which the Tower is located. The Treaty of 1868 guaranteed this region to the Indians. In 1874, in violation of this treaty, Gen. George A. Custer led a reconnaissance expedition into the Black Hills. As the result of his reports of the discovery of gold in paying quantities in the Hills, miners invaded the region. While the Government attempted to negotiate with the Indians to purchase the Hills, the Army endeavored to keep out the intruders. When the negotiations broke down in 1875, the troops were withdrawn and miners and settlers poured into the region. Towns such as Custer City and Deadwood sprung up over night. Many of the Indians, as a result, became convinced that they would lose their reservations in the Dakotas, Wyoming and Montana and joined the hostiles. By early 1876 the Government found a full-scale Indian war on its hands. Following the battle of the Little Bighorn in June, the Army pursued the hostile groups relentlessly. In the fall of that year the Indians were compelled to cede the Black Hills and most of their lands in Wyoming to the whites. For several years, however, small marauding groups continued to wander through the region. By the end of the decade, the vicinity around Devils Tower was comparatively safe for settlers. In the early 1880’s the first of these came into the Belle Fourche Valley in the vicinity of Hulett. With the exception of such outfits as the Camp Stool and the D (Driscoll), most of these settlers were small-scale farmers and ranchers from the mid-western states. In the vicinity of Moorcroft and the Tower, on the other hand, most of the land was occupied by large-scale outfits, such as the 101. From 1889 to 1892, the Chicago, Burlington and Quincy Railroad extended its line from the South Dakota State Line through Newcastle, Moorcroft and thence to Sheridan. From several points along this line, the Tower may be seen in the distance. It is not unreasonable to conjecture, therefore, that the railroad may have had some influence in the movement to give the area national protection.