The data for this report was collected during three raft trips down the Usumacinta River between the years of 1963-1970 to investigate the El Cayo area located between the sites of Piedras Negras and Yaxchilan. Evaluation of the environment, flora, and fauna and archaeological reconnaissance were undertaken, as well as test pit operations at the site of El Cayo and San Pablo Cave. Published by New World Archaeological Foundation.