|
||
Willow Mountain
Willow Mountain is on Rt. 118, about 2.5 miles north of Study Butte in the Big Bend region. It is not a large mountain, on the order of 500 feet, but it is a spectacular example of what geologists call "jointing."
When a body of molten rock is forced upward, near the surface, but not through it, and if it cools rapidly, vertical or near-vertical splits may form during cooling. Later, when the overlying material has been eroded away, these splits are exposed, and begin to weather away themselves. Here we see remnants of this erosion around the base of the mountain.
The top of this mountain has an altitude of 3,830 ft, and it is estimated to date from about 40 million years ago, about the middle of the volcanic era in Big Bend. Jointing can be seen in many places in the region, but none are better or purer examples of this process.