Red Gate Woods is a forest preserve section within the Palos Forest Preserve, a division of the Forest Preserve District of Cook County, Illinois. It is located near where the Cal-Sag Channel meets the Chicago Sanitary and Ship Canal. In the woods is the original site of Argonne National Laboratory and the Site A/Plot M Disposal Site, which contains the buried remains of Chicago Pile-1, the world's first artificial nuclear reactor.

Site A was a research facility near Chicago where, during World War II, research on behalf of the Manhattan Project was carried out. Operated by the University of Chicago's Metallurgical Laboratory, it was the site of Chicago Pile-2, a reconstructed and enlarged version of the world's first nuclear reactor, Chicago Pile-1. The first heavy-water reactor, Chicago Pile-3, was also constructed at this site. Research was carried out under contract to the United States' Office of Scientific Research and Development. After the war, the site became the first home of Argonne National Laboratory, a federally funded research and development center.