Digital Public Library of America: "The Digital Public Library of America [DPLA] brings together the riches of America’s libraries, archives, and museums, and makes them freely available to the world. It strives to contain the full breadth of human expression, from the written word, to works of art and culture, to records of America’s heritage, to the efforts and data of science." Use DPLA to find images and other kinds of sources - just search for topics in the San Luis Valley.
Google Books: Using Google Books, you can do very specific searches on a topic and see a preview of relevant pages in books. Some books may even be available in full text for free. If a book is not available in its entirety but you want it, try a search in the library catalog. If it's not there, scroll to the bottom where you can request it from another library.