Monte Desert of San Juan, Argentina, as Photographed by ASTP

Apollo-Soyuz photographs of the Monte Desert in southeastern San Juan, Argentina, were used for a reconnaissance survey of large-scale desert landforms. The Apollo-Soyuz color photographs were helpful in distinguishing lineaments and probable faults, drainage patterns, rock types, and soil-tonal variations. These photographs were especially useful in studying the distribution of sand deposits and large-scale dune morphology. The photographs reveal that the physiographic setting of the study area is characterized by mountain-and-bols6n topography controlled mainly by faulting. Most of the lineaments detected on the photographs appear to correspond to faults, and some of them may provide evidence of recent fault movement in the area. Typical topographic features include barren, deeply dissected block mountains bordered by slopes of alluvial materials that descend to a flat-floored desert basin. The most prominent features on the desert floor are two dune fields. The larger field lies south of the town of Vallecito and is approximately 1300 km2; the smaller dune field is near the town of Marayes and is approximately 160 km2. In the southern part of the Vallecito dune field, draa-size complex ridges display steep western flanks and gently sloping eastern flanks. These ridges are diagonally crossed by smaller linear "ational Air and Space Museum, Smithsonian