Topic summary
Puye escarpment
Extracted from the Wikipedia article Puye Formation.
Description
The Puye Formation is a fanglomerate containing 25 pyroclastic flows, including pumiciousignimbrites and block and ash flows, erupted by vents of the Tschicoma Formation. It is exposed from the mouth of Ancho Canyon in White Rock Canyon north to Santa Clara Peak, and generally underlies the Bandelier Tuff north and east of the city of Los Alamos, covering an area of 518 square kilometers (200 sq mi). It is best exposed in Guaje Canyon and on the southern end of the Puye escarpment where it is a cliff-forming formation. It is 71 meters (233 ft) thick at the type section but thickens westward towards the Sierra de los Valles, west of Los Alamos. Drilling has found that the formation is up to 221 meters (725 ft) thick. The formation was deposited between 7 and 4 million years ago, based on radiometric dating of an ash bed in the upper part of the formation and the absence of Bearhead Rhyolite ash (~7 million years old) in the formation.