GeoSnaps - Image of the Day
Geologic snapshots capturing Arizona’s geologic setting and mining history with a picture of the day from 1 January through 31 December 2013.
Check out previous GeoSnaps/Images of the Day.

26.5 MYBP (million years before the present) southern Arizona was the site of a cataclysmic volcanic eruption that formed the 12-mile-wide circular Turkey Creek Caldera. As shown in this graphic, huge clouds of volcanic ash and gas belched at supersonic speeds from ring dikes along the perimeter of the formative caldera. The resulting volcanic plume rose tens of miles high before collapsing into ground-hugging, pyroclastic flows that covered large parts of southeastern Arizona and western New Mexico. It is estimated that more than 120 cubic miles of molten rock was erupted. For more information, Guide to the Volcanic Geology of Chiricahua National Monument and Vicinity, Cochise County, Arizona, by John S. Pallister,l Edward A. du Bray, and Douglas B. Hall. The report and geologic map, including a number of field shots and colored illustrations are available online at the USGS Publication Warehouse - http://pubs.er.usgs.gov/publication/i2541
See our GeoSNAPs image of 27 November for a shot of the welded Turkey Creek Tuff, complete with explanation by geologist Wayne Ranney.