Scientists find evidence these occurrences drove early civilizations out of the Colorado Plateau.
Within the last three decades there have been large wildfires consuming the forests in nearly all the mountain ranges above the desert southwest. Just below the ranges, the lack of rains combined with invasive species has caused additional wildfires that have devastated portions of the Sonoran Desert. The link between drought and fire has pre-historic roots and host David Yetman and Tom Swetnam from the University of Arizona's Laboratory of Tree-Ring Research travel through the desert to higher elevations that contain evidence of drought, fire, and civilization. There is evidence that droughts drove early civilizations out of their dwellings on the Colorado Plateau and forced them to move nearer to the Rio Grande River. Yetman also ventures through a dog-hair thicket that has become dangerous because of previous land management practices and the lack of regular fire to regulate its growth. Additionally featured in this episode is a hike through Organ Pipe Cactus National Monument to see how scientists study the adaptability of desert plants to long-term and short-term droughts.