Daniel Griffin, University of Minnesota (image) University of Arizona Caption University of Arizona tree-ring researcher Daniel Griffin collects a core from the trunk of a ponderosa pine to study the tree's annual growth rings. He measures the width of such rings to study the monsoon rainfall history of the America Southwest. Credit (c) Scott St. George, University of Minnesota Usage Restrictions This image may only be used to accompany a story about the research described in the release, Monsoon Failure Key to Long Droughts in Southwest Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.