Why do gorges have steep walls?

Answer: Rivers cut down through resistant rock faster than the valley walls retreat

Rivers cut down through resistant rock faster than the valley walls retreat ✓ — Correct! A gorge forms where a river cuts down through resistant rock faster than the valley walls erode sideways. That keeps the walls steep and the valley narrow instead of letting it widen into a broad valley.

Earthquakes split the crust along faults and leave steep-walled fissures — Wrong. Earthquakes can fracture rock and create steep fault scarps, so sudden broken ground can look abrupt. But they do not carve a continuous valley floor downward; gorges require long-term river downcutting that outpaces wall retreat.

Glaciers scour downward along established valleys and leave steep-sided troughs — Wrong. Glaciers do scour bedrock and can leave steep valley sides, so the steepness alone is not the clue. But glacial erosion mostly broadens valleys into U-shapes; it does not make the narrow, river-cut V-shaped gorges asked about.