Block mountains, also known as fault-block mountains or graben mountains, are formed when large blocks of Earth's crust are uplifted and tilted along fault lines. These mountains are characterized by steep, rugged slopes on one side and gentler slopes on the other side. They are commonly found in areas with active tectonic activity, such as along plate boundaries or in regions where faults are prevalent.

Formation of Block Mountains:
Block mountains are formed through a process called faulting. When tectonic forces cause the Earth's crust to crack or break along a fault line, large blocks of crust are created. These blocks can either move upwards (uplift) or downwards (subsidence) along the fault plane. In the case of block mountains, the blocks move upwards, resulting in the formation of elevated mountainous regions.

Examples of Block Mountains:
1. Sierra Nevada, USA:
- The Sierra Nevada mountain range in California, USA, is a classic example of block mountains.
- It was formed due to the uplift of large blocks of crust along the Sierra Nevada fault system.
- The eastern slope of the Sierra Nevada is steep and rugged, while the western slope is more gentle.

2. Harz Mountains, Germany:
- The Harz Mountains in Germany are another notable example of block mountains.
- These mountains were formed as a result of faulting and uplift along the Rhenish Massif fault system.
- The Harz Mountains have steep slopes on their northern side and gentler slopes on the southern side.

3. Vosges Mountains, France:
- The Vosges Mountains in France are a picturesque example of block mountains.
- They were formed through the uplift of crustal blocks along the Vosges fault line.
- The western side of the Vosges Mountains features steep slopes, while the eastern side has more gradual slopes.

4. Wasatch Range, USA:
- The Wasatch Range in Utah, USA, is a well-known block mountain range.
- It was formed as a result of faulting and uplift along the Wasatch Fault.
- The western side of the range exhibits steep cliffs and canyons, while the eastern side has a more gentle slope.

Conclusion:
Block mountains are fascinating geological features that result from the movement of large crustal blocks along fault lines. They are characterized by steep slopes on one side and gentler slopes on the other. Examples such as the Sierra Nevada, Harz Mountains, Vosges Mountains, and Wasatch Range showcase the diverse formations and appearances of block mountains around the world. Understanding the formation and characteristics of these mountains provides valuable insights into the dynamic nature of Earth's crust.

Block mountain example