10,000 years ago the climate in Big Bend was cooler and wetter, and the woodland ecosystem around you would have covered the landscape as far as the eye can see. As the climate slowly became warmer and drier, the woodland species could no longer survive in the lower elevations, and more desert-adapted species moved in to take their place. Today, mountains like the Chisos protect small relict populations of once-widespread plants, animals, and other organisms that are isolated here by the surrounding desert.