The elevation in the Chihuahuan varies from about 1,750 to 6,000 feet, as there are several larger mountain ranges, such as the Organ Mountains, the Guadalupe Mountains, and the Chiracahua Mountains, plus many smaller mountain ranges contained in the area, namely the San Andres and Doña Anas in New Mexico, the Franklin Mountains and the Davis Mountains. The Chihuahuan is a rain shadow desert, formed between two mountain ranges (the Sierra Madre Occidental on the west and the Sierra Madre Oriental on the east) which block oceanic precipitation from reaching the area. The Chihuahuan Desert is considered the most biologically diverse desert in the Western Hemisphere and one of the most diverse in the world, and includes more species of cacti than any other desert in the world. The most prolific plants in this region are agave, yucca and creosote bushes, in addition to the ubiquitous presence of various cacti species.