Stebbins Gulch Joints

Classic Example of Joints

Notice the parallel linear breaks in a silty shale layer within the Cleveland Shale. These breaks are called “joints,” and usually occur in parallel groupings known as “joint sets.”  Visitors sometimes confuse rock joints with geologic faults. They are not the same.  A joint is simply a planar break or fracture in rock. It shows parting without shear displacement.  For a fault to form, the rock masses on either side of the break have to slide vertically or horizontally in relation to each other. There is no evidence that this is what happened here.  These joints are so perfect that they almost look like they were cut by a pavement saw.  The direction and orientation of joints are often plotted on geologic maps. Such measurements can be helpful in determining directional stresses on a particular body of rock. 

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