Understanding certain aspects of structural geology can be challenging for undergraduates, and the good people at "On the Cutting Edge" have worked to create this useful resource to help students and educators. This particular lesson plan was created by Paul Kelso of Lake Superior State University, and it was designed for students who have a bit of background knowledge of structural geology. The activity will help students learn about the concept of Mohr-Coulomb failure and also afford them a physical understanding of conjugate fracture/fault systems. As with other plans offered in this series, the piece provides information on the necessary materials (such as clay) required for the activity, along with teaching tips, assessment tools, and techniques.