A fault block mountain is formed when a block of the Earth's crust is uplifted or downthrown relative to the surrounding area by the movement of a fault. This movement can be caused by a variety of forces, including the collision of two tectonic plates, the movement of magma beneath the Earth's surface, or the collapse of a volcanic caldera.

When a tectonic plate collides with another plate, it can cause the crust of the Earth to buckle and fold, creating mountains. This type of mountain building is common in areas where two continental plates are colliding, such as the Himalayas.

The movement of magma beneath the Earth's surface can also cause fault block mountains to form. When magma rises to the surface, it can create a dome-shaped uplift in the crust. If this uplift is large enough, it can cause the surrounding crust to fracture and create a fault block mountain. This type of mountain building is common in areas where there is volcanic activity, such as the Basin and Range Province in the western United States.

The collapse of a volcanic caldera can also create a fault block mountain. When a volcano collapses, it can create a large depression in the Earth's crust. This depression can be surrounded by a series of fault blocks that have been uplifted by the collapse. This type of mountain building is common in areas where there has been volcanic activity, such as the Yellowstone Plateau in the western United States.