The average width (east-and-west) is less than 160 kilometers (100 miles) but it extends from the Peruvian border 1000 kilometers (600 miles) south to the Bolivian Altiplano. The mountains nearest the ocean are the Pacific coastal range, with an average elevation of 800 meters (2500 feet). The Cordillera Domeyko, a range of foothills of the Andes Mountains, lies east.
The Atacama Desert is the driest desert of the globe and it is virtually sterile because it is blocked from moisture on both sides by the Andes mountains and by coastal mountains. The Atacama is 15 million years old and 50 times more arid than California's Death Valley. The driest part of the Atacama is an area called the 'double rain shadow.' In 2003 a team of researchers published a report in Science magazine titled "Mars-like Soils in the Atacama Desert, Chile, and the Dry Limit of Microbial Life" in which they duplicated the tests used by the Viking 1 and Viking 2 Mars landers to detect life, and were unable to detect any signs in Atacama Desert soil. The region may be unique on Earth in this regard.
The Atacama is inhabited, though sparsely populated. The Pan-American Highway runs through the Atacama, and in the center of the desert, at an altitude of some 2000 meters, is the village of San Pedro. Its church is recent, having been erected by the Spanish in 1577, but archeological evidence indicates that the San Pedro area was the center of a Paleolithic civilization that built rock fortresses on the steep mountains encircling the valley.