Fault-block mountains are formed when deep areas of bedrock are broken into faults. These faults leave steep, vertical displacements in the Earth's crust. The vertical motion of dropped blocks and lifted blocks is often accompanied by tilting, which creates high, sheer cliffs. These blocks are formed when the Earth's crust is stretched and pulled apart by tectonic forces.

There are two types of block mountains: lifted and tilted. The tilted block mountains have a gentle slope on one side and a steep side with an exposed scarp, or bluff. The Grand Tetons are an example of tilted block mountains. The tilted faults in the Grand Tetons were caused when swelling under the rock broke the rock layers into perpendicular faults. Lifted block mountains have two steep sides with scarps on each side. These mountains are caused by rock layers that are stretched in different directions, forming pushed up blocks called horsts. Dropped blocks are called graben.