promoted the settlement of the public domain, and the nation's population center shifted steadily westward.
The key to settlement expansion was transportation. Before 1830, the location and spread of American settlements was influenced by sail and wagon technology. Eastern seaports and growing centers on the inland waterways were preeminent. From the 1830s to the 1870s, the steamboat and the iron-based railroad were the principal innovations, and ports with large railroad hinterlands grew to dominance. In the 1870s, the East still had most of the nation's cities and population and most of the private and cultivated land. The West, especially west of the Mississippi, which had most of the public lands, was scantily settled. However, the Mississippi had been bridged, and in 1869 the golden spikes made the final link in the transcontinental railroad connecting the East and California.
After the Civil War, pressure mounted for more knowledge about the natural resources of the West as the pace of territorial expansion, technological innovation, and burgeoning industrialization quickened. The need for an increasing and continuous flow of resources to fuel the Industrial Revolution led the federal government for the first time to spend money on scientific investigations. Four congressionally authorized and funded geographic and geologic surveys of the West were conducted from 1867 to 1879. These surveys—headed by Clarence King, George M. Wheeler, Ferdinand V. Hayden, and John Wesley Powell—often are referred to as “The Great Surveys.” Parties of scientists, surveyors, photographers, and journalists made these regional surveys. The survey reports made major contributions to our understanding of the West. King's survey, for example, explored the land along the fortieth parallel through which the first transcontinental railroad was built. Some scientists criticized the practical nature of the regional surveys.
Laws such as the Homestead Act of 1862 and the General Mining Law of 1872 (NRC, 1999a) were passed by Congress to encourage settlement of the nation's interior and to facilitate the extraction of mineral, energy, and other resources to power industrialization. The Homestead Act allowed persons to obtain 160 acres of public land free by proving residency on the land for five years. The General Mining Law allowed persons to stake claims on the federal lands of the western United States without payment of royalty to the federal government and without acquiring title to the land itself. Consequently, the development of natural resources over much of the nation proceeded in an uncoordinated and at times thoughtless fashion that led eventually to calls for more