Streams that enter the northern half of the San Luis Valley of south-central Colorado, a relatively flat basin, rarely reach the Rio Grande. Despite the fact that the San Luis Valley is a true desert—receiving less than 8 inches of precipitation a year—much of the valley supports a vigorous agricultural industry because of irrigation water from deep artesian wells, some of which tap as many as five or six artesian aquifers. Visible are a large alluvial fan at the northern end of the valley that exhibits the classic pattern found in arid, flat landscapes; San Luis Creek; and San Luis Lake. A smaller, similarly colored drainage feature is also observed at the top center of the photograph. The two highly reflective areas north and south of the cultivated fields are probably the result of accumulations of salt deposited in the soils by the evaporation process.