Named for the Texas persimmon trees growing here, Persimmon Gap is an ancient place. Almost 300 million years ago, this area was a great mountain range. But even as the mountains rose, erosion wore them down. After millions of years, only gentle hills remained. Then the land slowly subsided until, 150 million years ago, a sea covered this area and buried the hills with sediment. Later, the same uplift that raised the Rocky Mountains raised the present-day Santiago Mountains around you. Their creation thrust up the long-buried rock from the older mountains. In the hills across the road from the visitor center that ancient rock is exposed...the oldest rock in the park!