Fault blocks are very large blocks of rock, sometimes hundreds of kilometers long, created by tectonic stresses and located in the Earth's crust "Crust (geology)"). Large areas of bedrock are divided into blocks by faults. The blocks are characterized by relatively uniform lithologies. The largest of these fault blocks are called crustal blocks. The large blocks of the Earth's crust detached from tectonic plates are called terranes.[1]​ The terranes that occupy the entire thickness of the lithosphere are called microplates. Continent-sized blocks are variously called microcontinents, continental ribbons, H blocks, extensional allochthons, and outer maxima. [2]​.

Because most stresses are related to the tectonic activity of moving plates, most movement between blocks is horizontal, that is, parallel to the Earth's crust via strike-slip faults. However, moving blocks vertically produces much more dramatic results. Landforms (mountains, hills, ridges, lakes, valleys, etc.) are sometimes formed when faults have a large vertical displacement. Adjacent raised blocks (tectonic massifs or horsts) and sunken blocks (tectonic grabens or grabens) can form high escarpments. Often the movement of these blocks is accompanied by tilting, due to compaction "Compaction (geology)") or stretching of the crust at that point.

Fault-block mountains are often the result of rifting, an indicator of extensional tectonics. These can be small or form extensive rift valley systems, such as the East African Rift zone. Death Valley in California is a smaller example. There are two main types of block mountains: uplifted blocks between two faults and tilted blocks controlled primarily by one fault.

Raised-type block mountains have two steep sides exposing both side scarps, giving rise to massif and graben terrain seen in several parts of Europe, including the Upper Rhine Valley, a graben between two massifs: the Vosges mountain range (in France) and the Black Forest (in Germany), and also the Rila-Rhodope massif in Bulgaria, southeastern Europe, including the well-defined tectonic massifs of Belasica (linear massif), the Rila Mountains (domed dome-shaped massif) and the Pirin mountain range, a massif that forms a massive anticline located between the complex valleys of the Strymon and Mesta tectonic trenches.[3]​[4]​[5]​.