Final answer:
Horsts are elevated blocks of Earth's crust bordered by faults, while grabens are the sunken blocks in between. These geological structures commonly occur in tectonically active areas, such as rift zones like the Great Rift Valley in Eastern Africa and are examples of features created by crustal extension.
Step-by-step explanation:
Horsts and grabens are geological structures that result primarily from the process of crustal extension. A horst is an elevated block of the Earth's crust bordered by parallel faults, lying between two down-dropped blocks known as grabens or rift valleys. They are typically formed due to the extension and fracturing of the Earth's crust, which produces a series of fault blocks. These types of formations can often be seen in rift zones or areas of continental rifting.
Horsts and grabens can be found in various parts of the world. For example, the Great Rift Valley in Eastern Africa, which stretches from the Middle East down through Eastern Africa, consists of a series of grabens. The Vosges Mountains in France and the Black Forest in Germany are examples of horsts. They are particularly common in regions of tectonic activity where the crust is being pulled apart, such as along divergent plate boundaries.