There are some large collections of genealogical and historical significance that hardly ever get a mention in the media. When was the last time you checked out the collection in the Denver Public Library. However, the "Genealogy Collection, begun in 1910 under the direction of City Librarian Chalmers Hadley, offers an extensive collection of genealogical and historical sources numbering about 60,000 volumes and 75,000 pieces of microform, as well as magazines, charts, clippings, and manuscripts. The collection at the Denver Public Library constitutes the largest collection in the Rocky Mountain area, and the second largest between the Mississippi River and the West Coast. The Library also has many useful online resources."
One very useful source is the Colorado Historic Newspapers Collection. "The Colorado Historic Newspapers Collection (CHNC) currently includes 147 newspapers published in Colorado from 1859 to 1923. CHNC contains over 477,000 digitized pages and is a joint endeavor of the Colorado State Library, the Colorado Historical Society, and generous donors throughout the state."
Also check out the links to the Colorado State Library and the Colorado Historical Society.