Each collection has a separate overview of what can be accessed; here is the description for "The Evolution of the Conservation Movement, 1850-1920":
The Evolution of the Conservation Movement, 1850-1920 documents the historical formation and cultural foundations of the movement to conserve and protect America's natural heritage, through books, pamphlets, government documents, manuscripts, prints, photographs, and motion picture footage drawn from the collections of the Library of Congress.
The collection consists of 62 books and pamphlets, 140 Federal statutes and Congressional resolutions, 34 additional legislative documents, excerpts from the Congressional Globe and the Congressional Record, 360 Presidential proclamations, 170 prints and photographs, 2 historic manuscripts, and 2 motion pictures.Lots of fun stuff to look at over the various collections. I know one of you is working on a paper about Woody Guthrie: his correspondence has been digitized and is available on the site at http://memory.loc.gov/ammem/wwghtml/wwghome.html .
American Environmental Photographs Collection, [AEP Image Number AEP-CAS207],
Department of Special Collections, University of Chicago Library.
From "American Environmental Photographs, 1891-1936" :
"This collection consists of approximately 4,500 photographs documenting natural environments, ecologies, and plant communities in the United States at the end of the nineteenth and the beginning of the twentieth century. Produced between 1891 and 1936 by a group of American botanists generally regarded as one of the most influential in the development of modern ecological studies, these photographs provide an overview of important representative natural landscapes across the nation. They demonstrate the character of a wide range of American topography, its forestation, aridity, shifting coastal dune complexes, and watercourses. Comparison of early photographs with later views highlights changes resulting from natural alterations of the landscape, disturbances from industry and development, and effective natural resource usage. The photographs were taken by Henry Chandler Cowles (1869-1939), George Damon Fuller (1869-1961), and other Chicago ecologists on field trips across the North American continent.
"Among the natural features these images document are ecological settings such as dunes, bogs, forests, and deserts; individual plants from the Ponderosa pine and birch to grasses and mosses; landscape features like the Grand Canyon, Lake Superior, and the Sierra Nevada; and the consequences of natural and human changes to the environment ranging from erosion and floods to irrigation and lumbering. The collection also includes photographs of University of Chicago botanists as they conducted field research, led students on summer field classes, and traveled across the North American continent on tours including the International Phytogeographic Excursion of 1913."Hope this is helpful to some of you.