Small aggregate quarry in a Pleistocene-age cinder cone of the Springerville volcanic field of eastern Arizona. This monogenetic volcanic field comprises over 400 cinder cones covering more than 3000 square kilometers. The field was active from about 2 million years to 300,000 years ago.
Chris Condit and his fellow graduate students at the University of New Mexico did a marvelous job mapping the volcanic stratigraphy and establishing the geochronology of the field.
For a non-technical overview of the Springerville field, see John Bezy's and Aurthur Trevana's 'A Guide to the Geology of the White Mountains and the Springerville Volcanic Field, Arizona'. http://repository.azgs.az.gov/uri_gin/azgs/dlio/1536