Rift block mountains and valleys are formed when the Earth's crust is stretched and pulled apart. This can happen when two tectonic plates are moving away from each other, or when a single plate is being stretched and thinned. As the crust pulls apart, it creates a series of parallel faults, which are cracks in the Earth's surface. These faults are often accompanied by volcanic activity and earthquakes.

The blocks of crust between faults are called rift blocks. As the crust pulls apart, the rift blocks are tilted and uplifted, forming mountains. The valleys between the mountains are called rift valleys.

Rift block mountains and valleys are common features in many parts of the world, including the Great Rift Valley in Africa, the Basin and Range Province in the western United States, and the Rhine Rift Valley in Europe.

Rift block mountains and valleys can have a significant impact on the landscape. They can create steep slopes and rugged terrain, which can make transportation and construction difficult. They can also disrupt water drainage patterns and create wetlands and lakes. However, rift block mountains and valleys can also create beautiful scenery and provide habitat for plants and animals.