Fault-block or fault mountains are produced when normal (near vertical) faults fracture a section of continental crust. Vertical motion of the resulting blocks, sometimes accompanied by tilting, can then lead to high escarpments. These mountains are formed by the earth's crust being stretched and extended by tensional forces. Tilted blocks are common in the Basin and Range region of the western United States. Level blocks lead to the horst and graben terrain seen in northern Europe. Fault block mountains commonly accompany rifting, another indicator of tensional tectonic forces.
Block mountains can also be referred to as a horst. It is a steep-sided mountain, formed where a block of the earth's crust has been squeezed upward between two parallel fault lines. Two types of block mountains are lifted and tilted. Lifted type block mountains have two steep sides exposing both sides scarps. Tilted type block mountains have one gently sloping side and one steep side with an exposed scarp.
Schematic of the formation of Fault-Block Mountains.
References
Monroe, James S., and Reed Wicander. The Changing Earth: Exploring Geology and Evolution. 2nd ed. Belmont: Wadsworth Publishing Company, 1997. ISBN 0-314-09577-2 (pp. 234,-8)'
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