Highly reflective White Sands National Monument in south-central New Mexico, the world’s largest gypsum sand field, receives its interior drainage primarily from the San Andres Mountains to the west and the Sacramento Mountains to the east. The southwest corner of White Sands National Monument, the lowest spot in the Tularosa Valley and showing a dark accumulation of moisture, changes from a dry lakebed into Lake Lucero when summer rain falls. Manmade features visible in the photograph include weapons impact target areas (large circular features at the top of the photograph); a linear U.S. Air Force test facility along the eastern side of the San Andres Mountains; the barely discernible alternate landing site for the NASA Space Shuttle (a white linear feature in the northwest section of the monument; and the long [approximately 10 miles (16 kilometers)] linear rocket sled test bed, part of Holloman Air Force Base, east of the monument.