built. 1130 Pueblo Bonito is four stories tall and contains 800 rooms 1130-1180 Fifty-year drought in the Southwest. Rain and snow cease to fall. Alluvial groundwater declines, floodplain erosion occurs. Dry-farming zone reduced, crop production potential decreased. Severe arroyo cutting and depression of alluvial groundwater. Severe environmental stress. 1140–1150 Collapse of the Ancestral Puebloan culture at Chaco Canyon. 1150 Great Houses empty 1180 Sunset Crater erupts for the second time. 13th century 14th century 15th century 16th century 1539 Marcos de Niza erroneously describes the pueblo of Háwikuh as the Seven Cities of Gold. 17th century 1680-1692 The Pueblo Revolt of the Pueblo people against Spanish colonists in the New Spain province. 1774 Don Bernardo de Miera y Pacheco identifies the Chaco Canyon area as "Chaca" on a map. The term, a Spanish translation of a Navajo word, is thought to be the origin for "Chacra Mesa" and "Chaco". 18th century 19th century 1844 Josiah Gregg refers to the Chaco pueblos in his book Commerce of the Prairies, making its first appearance in popular culture. 1849 Lt. James H. Simpson leads the Washington Expedition, a military reconnaissance team which surveys Navajo lands and records cultural sites in Chaco Canyon. Illustrations created by the Kern brothers are included in a government report. 1877 Artist and photographer William Henry Jackson participates in the Hayden Survey of the Western United States, producing maps of Chaco Canyon, but no photographs due to technical problems. 1888 Richard Wetherill and Charlie Mason find the Cliff Palace, Spruce Tree House and Square Tower House. Chaco Canyon is surveyed and photographed by Victor and Cosmos Mindeleff of the Bureau of American Ethnology 1896 Richard Wetherill begins excavating Chaco Canyon 1896-1899 George H. Pepper from the American Museum of Natural History leads the Hyde Exploring Expedition in excavating Pueblo Bonito 20th century 1901 General Land Office special agent S. J. Holsinger recommends creating a national park to preserve archaeological sites in Chaco Canyon 1907 Chaco Canyon National Monument is established. 1928-1929 American astronomer and University of Arizona professor A. E. Douglass participates in a National Geographic Society research project exploring Chaco Canyon. Using his newly invented technique of dendrochronology, Douglass dates Chetro Ketl and dozens of Chacoan sites Expedition under Neil Merton Judd to collect dendrochronological specimens to date habitation of Chaco Canyon 1937 A Civilian Conservation Corps of Navajo stonemasons repairs Chacoan buildings in Chaco Canyon. A previous