El Pinacate and Gran Desierto de Altar are known for their unique physical and biological characteristics, by the presence of a volcano shield, and by the extensive areas of active dunes that surround them.  They have the greatest concentration of Maar craters. The Pinacate mountain range has orogenic features of high interest for its abrupt formation of volcanic eruptions, that accumulated lava in compacted rocks, sand and volcanic ashes which then formed colors of spectacular beauty and the craters: El Elegante, Cerro Colorado, MacDougal and Sykes.