Station 4 Joints

Joints 

Joints control the shape and distribution of most pinnacles at City of Rocks. A joint is a type of extension fracture formed by movement of the rock in a direction perpendicular to the plane of fracture. Joints form in solid rock that is stretched and its brittle strength (the point at which it breaks) is exceeded. When this happens, the rock fractures. 

The presence of joints allows water to infiltrate the rock and makes the granite vulnerable to weathering. The joints also trap soils, creating micro-habitat for a number of cliff-loving plants, such as ferns, limber pine, and pink alumroot.