An overthrust fault is also known as a thrust fault or a reverse fault. It occurs when one block of rock is pushed up and over another block of rock in a horizontal motion. The movement of the rocks will be along the plane of the fault, with the overlying rock moving horizontally towards the other block of rock that is underneath the ground. The other synonyms for overthrust fault include thrust zone, thrust system, and underthrust. These terms are used interchangeably and refer to the geological phenomenon that causes the movement of rocks along a fault plane. Overthrust faults are common in mountainous areas and can be seen as folded and faulted rocks.