Many of the documents on microfilm may now be available in digital form. You can start with the catalog to determine the title, author, and date, and then go out and search for the documents online. Microfilm and microfiche can be accessed on the 2nd floor near the map cases. Please ask at the Research Help Desk for assistance.
Special Collections and Archives may have rare publications of interest to your topic, and the William H. Nelson papers do contain documents regarding water agreements between the U.S. and Mexico that may be useful for those interested in the issues around natural resource allocations.
A sample of collections at the Library of Congress with material relevant to the US-Mexico borderlands. Searching for "Mexico" should help you find other collections where at least some portion of the material relates to the history US-Mexico relations and the changing border.
The tools you use to find primary sources will be individual to your topic. You can ask questions like where, when, why, how to brainstorm digital collections that may exist for your topic. Keep these especially in mind:
You can also use your secondary sources to get an idea of where primary sources might exist. Take a look at the references in the bibliography and see where the author(s) found their primary sources.
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