American West Based on sources from the Everett D. Graff Collection of Western Americana at the Newberry Library, Chicago, a unique resource widely regarded as one of the finest collections of Western Americana in existence, this collection includes a mixture of original manuscripts, maps, ephemeral material and rare printed sources.
Arizona Archives Online An online description to archival materials. Includes finding aids from the various special collections of Arizona State University, University of Arizona and Northern Arizona University
Colorado Plateau: Canyons, cultures and environmental change "This website provides an introduction to the environmental history of the Colorado Plateau. It summarizes a vast body of research from multiple disciplines"
Mountain Men and the Fur Trade: "These documents are accounts of the Rocky Mountain fur trade during the first half of the 19th century. Most of these are either primary or secondary historical sources, and have been transcribed from printed or manuscript form."
Mountain West Digital Library The Mountain West Digital Library is a central search portal for digital collections about the Mountain West region providing free access to 300,000 resources in over 350 collections from universities, colleges, public libraries, museums, archives, and historical societies in Utah, Nevada, and other parts of the U.S. West.
Online Archive of California. An excellent site that provides access to several important California collections covering among other topics the Free Speech Movement, Japanese-American Relocation, and California oral histories.
Portal to Texas History The Portal is a gateway to Texas history materials. From prehistory to the present day, you can explore unique collections from Texas libraries, museums, archives, historical societies, genealogical societies, and private family collections.
Regional Oral History Office - UC-Berkeley As a division of The Bancroft Library, the Regional Oral History Office preserves the history of the San Francisco Bay Area, California, and the Western United States. By conducting carefully researched, tape-recorded, and transcribed interviews, ROHO creates archival oral histories intended for the widest possible use.
Trails of Hope: Overland Diaries and Letters, 1846 - 1869 Builds upon the overland trail diaries and letters found in the rich collections of the L. Tom Perry Special Collections, Lee Library, Brigham Young University; Special Collections, Marriott Library, University of Utah; and Special Collections, Merrill Library, Utah State University. The years 1846-1869 are significant, representing the Mormon exodus from Nauvoo, Illinois, the joining of the Union Pacific and Central Pacific railroads at Promontory Point, Utah, and the ending of the overland pioneer era.
WestWeb: "WestWeb is a topically-organized website about the study of the American West..."
Yahoo - U. S. History - 19th Century - American West
The first place to start for a search of Internet sites for U. S. History. Particularly useful for tracking down sites with primary sources. Its hierarchical arrangement is as close to a library as one gets on the web.