The American West is well on its way into one of the worst mega-droughts on record, a new study warns, a dry period that could last for centuries and spread from Oregon and Montana, through the Four Corners and into West Texas and northern Mexico.

Several other mega-droughts, generally defined as dry periods that last 20 years or more, have been documented in the West going back to about 800 A.D. In the new study, the researchers, using an extensive tree-ring history, compared recent climate data with conditions during the historic mega-droughts.

Read the full article from Bob Berwyn with San Antonio Express-News here.