Trans-Pecos Volcanic Field

The Trans-Pecos Volcanic Field is a volcanic field located in Western texas in the counties of Brewster, Jeff Davis, Presidio, and extends into northern Mexican states of Chihuahua and Coahuila. It is the southern most Volcanic field to be documented and recorded in the Continental United States. The Field started volcanic activity around 48 MYA in the middle Eocene period, and ended around 31 million years later in the miocene period. 
Most of the volcanoes in the field are Calderas. Some of the volcanoes are:
The field is currently undergoing geological studying and researched by several colleges and the United States Geological Survey.