Between roughly 900 and 1260 AD there was a massive drought that severely impacted the plants, animals and people of the Southwest. Now referred to as the Medieval Drought, the best records of this phenomenon can be found within the trees that lived through this difficult time period. Host David Yetman hikes with Tom Swetnam from the University of Arizona's Laboratory of Tree-Ring Research through the White Mountains of California and Sequoia National Park to observe how scientists use tree rings to gather evidence of climate conditions from thousands of years ago. By taking a core sample from the bristle cone pines of the White Mountains, scientists learned of this Medieval Drought and roughly how long it lasted. Some of the dead and downed sequoias in Sequoia National Park corroborate this information with evidence of the drought in their tree rings. This episode also offers an examination of the ruins of some of the people most affected by the drought, the Anasazi Indians, at Bandelier National Monument, a trek through a "ghost forest" and a first-hand look at "yoda" trees.