As part of the Navajo-Gallup Water Supply Project, the Bureau of Reclamation was tasked with design and construction of infrastructure to treat and deliver potable water to the communities of Navajo Nation, parts of the Jicarilla Apache Nation, and City of Gallup. The Bureau of Reclamation has been evaluating the Public Service Company of New Mexico's (PNM) San Juan Generating Station (SJGS) reservoir as a possible water storage and sediment settling basin for the Navajo-Gallup Water Supply Project. The U.S. Geological Survey (USGS), in cooperation with the Bureau of Reclamation, was tasked with collecting reservoir sediment cores and pore water from SJGS reservoir. This data release contains reservoir sediment descriptions, sediment inorganic and organic chemistry, and pore water inorganic chemistry.