Geology
The Jemez Mountains lie to the north of the Albuquerque Basin in the Rio Grande rift. They are a classic example of intracontinental volcanism and consist of a broadly circular ridge surrounding the famous Valles Caldera. The most recent known eruption was a basalt flow dated to 50,000 to 60,000 years before the present; however, most of the volume of the range is composed of rhyolite. The two most recent caldera-forming eruptions, dated to about 1.4 million and 1.1 million years ago, produced massive ignimbrite deposits known as the Otowi and Tshirege members, respectively, of the Bandelier Tuff. Much of the material in these deposits now forms the Pajarito Plateau, a scenic region of canyons and mesas on which Los Alamos is situated. Redondo Peak, the second highest summit in the range at 11,254 ft (3431 m), is a resurgent dome in the middle of the Valles Caldera, which also contains several smaller volcanos. The caldera is segregated by these structures and its rim into multiple lush grass valleys (valles in Spanish, hence the name).
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