Origins of the American Conservation Movement 1850-1920
The following link will take you to the Library of Congress's website. The Library of Congress houses an extensive collection of materials outlining the origins of American Conservationism---most of which originated in the Progressive Era. For example, key in the words "Hetch Hetchy" and see what sort of documents are housed in the Library. Also try "Theodore Roosevelt". I do not expect you to do primary research on this topic. I am just interested in showing you what sorts of materials are available in the Library of Congress for historians and other researchers on this topic.