transform plate boundary formed on the western United States along the San Andreas Fault. Lateral extension of the Colorado Plateau occurred as a result, forming topographic relief and mountainous features along crustal extension features in the Basin and Range province, such as the Rio Grande rift west of the Guadalupe Mountains. A mechanism similar to extension in the Rio Grande rift is thought to have generated topographic relief in the Guadalupe Mountains, and the timing of topographic relief generation has been estimated to ~20 million years ago using cave speleothem records and interpreted to reflect drainage of subsurface aquifers as topographic relief was generated along the margin of the mountain range. The Guadalupe Mountains are mainly carved by a series of NW-SE trending canyons leading to exposure of marine rocks at their current elevation. In the dry, semi-arid environment, continuous limestone bedrock of the Capitan Reef forms large prominent cliffs traceable across the landscape. These cliffs are typically exposed along the eastern edge of the park. Groundwater circulating through deep fractures dissolves limestone and forms extensive cave networks, including the Carlsbad Caverns. Ecology Three major ecosystems are contained within the mountain range. First, deserts exhibit salt flats on the western side of the national park and creosote desert, with low elevations on the east covered with grassland, pinyon pine, and junipers such as alligator juniper and one-seeded juniper. Secondly, canyon interiors such as McKittrick, Bear, and Pine Springs Canyon on the southeast end exhibit maple, ash, chinquapin oak, and other deciduous trees. These trees are able to grow in the desert due to springs of water recharged by wet uplands. Finally, alpine uplands known as "the Bowl" exceeding elevations of are covered with denser forests of ponderosa pine, southwestern white pine, and douglas-fir, with small stands of aspen. The range contains many world-class caves, including Carlsbad Caverns (the best known) and Lechuguilla Cave, discovered in 1986. The history of the range includes occupation by ancient Pueblo and Mogollon peoples, and by the Apache and various Anglo outlaws in the 19th century. See also Beach Mountains Trans-Pecos References External links Mountain ranges of New Mexico Mountain ranges of Texas Landmarks in Texas Landforms of Eddy County, New Mexico Carlsbad Caverns National Park Guadalupe Mountains National Park Landforms of Culberson County, Texas Landforms of Hudspeth County, Texas