The type of mountains that form at large-scale normal faults where the footwall and hanging wall spread apart from each other are called horst and graben mountains.

Here's a breakdown:

* Normal Fault: A normal fault occurs when the hanging wall (the block of rock above the fault) moves downward relative to the footwall (the block of rock below the fault). This movement is caused by tensional forces pulling the crust apart.

* Horst: A horst is an elevated block of land bounded by normal faults on both sides. It's essentially a "block mountain" that has been uplifted relative to the surrounding terrain.

* Graben: A graben is a depressed block of land bounded by normal faults on both sides. It's essentially a valley that has been dropped down relative to the surrounding terrain.

Formation: When large-scale normal faults develop, they often occur in parallel sets. The blocks between these faults can either be uplifted (forming horsts) or dropped down (forming grabens).

Examples:

* The Basin and Range Province in the western United States: This region is characterized by alternating horsts and grabens, creating a distinctive landscape of rugged mountains and flat-floored valleys.

* The Rhine Graben in Europe: This graben is a long, narrow valley formed by a series of normal faults.

Key takeaway: Horst and graben mountains are a unique type of mountain formation that results from the extensional forces associated with normal faults. They are characterized by alternating uplifted blocks (horsts) and depressed blocks (grabens).