What is a fault?

   Fault is a fracture or break in the earth's crust along which movement has occurred. The earth on one side of the fault may move upward, downward, or sideward in relation to the other side of the fault. As a result, cliffs and basins and troughs may be formed. Faulting in layered rocks may result in one layer being raised or lowered or tilted in relation to the same layer on the opposite side of the fault. Faults generally accompany mountain building.