A relatively unknown and inaccessible 150 kilometer segment of the Rio Grande in Texas and Mexico was the subject of an archaeological reconnaissance carried out during canoe expeditions of 1973 and 1976. Discoveries included 83 prehistoric and 5 historic sites, among which were caves and rockshelters, open campsites, quarries, candelilla wax camps, and ranch camps. The report provides descriptive data, habitational and environmental relationships, and evaluations of site potentials. The study concludes with an experiment in aboriginal subsistence techniques.