Technical Abstract: During his second voyage in 1492, Columbus introduced the first cattle to the New World. Since their introduction from Andalusia, these cattle have undergone 500 year sof co-evolution with the lanscapes of North and South America. Focusing on arid regions of Chihuahua, Sonora, and Baja California, we are undertaking a series of studies to better understand the arid land adaptations of "criollo" cattle and their potential effects on vegetation change. While the oldest breed in the United States, these cattle may again prove useful in shaping the future of the North American beef cattle industry.