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How do rift valleys create mountains with steep inward-facing slopes?

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A car drives along the Trans-Canada Highway with Mount Sir Donald's sharp, snow-capped peak rising above forested slopes in the Selkirk Mountains, British Columbia. — mountain Mount Sir Donald in the Selkirk Mountains, British Columbia, looms above a segment of the Trans-Canada Highway.

Rift valleys create mountains with steep inward-facing slopes primarily through the process of normal faulting associated with crustal extension.31

As lithospheric plates diverge, the Earth's crust stretches and thins, causing large blocks of rock to subside along steeply dipping fault planes. The blocks that drop downward form the floor of the rift valley, while the adjacent, relatively stationary or uplifted crustal blocks remain as high plateaus or mountain ranges. The steep, inward-facing slopes of these mountains are the direct result of the exposed fault scarps created by this downward displacement.231

In some instances, this process results in horst and graben topography, where a central block (the horst) remains elevated relative to the surrounding dropped blocks (the grabens), creating mountain ridges bounded by steep faults. Additionally, in areas where rift valleys form over large domes, the upwelling of hot material from the asthenosphere can cause thermal expansion and upward bulging of the crust, further contributing to the elevation of the surrounding terrain.241