Featured in this near-vertical photograph of south-central Colorado is part of the generally north-south-trending Sangre de Cristo Mountains with a snow-covered ridge line at elevations above 10 000 feet (3048 meters). Apparent are the sharply faulted slopes of the western side of the mountain range and snow-covered Blanca Peak [14 345 feet (4372 meters)]. Center-pivot irrigation (circular field patterns) has allowed the arid San Luis Valley to become an intensive agriculture region. Intermittently flowing San Luis Creek, a tributary of the Rio Grande, is barely visible as it flows south to merge with the Rio Grande near Alamosa. Dark San Luis Lake, southwest of Great Sand Dunes National Monument, lies along the drainage path of San Luis Creek. Barely discernible are two jet aircraft contrails and their shadows.