How do deep, narrow canyons form in rock?

Answer: Rivers cut downward into bedrock as the land slowly rises

Wind scours narrow channels into dry desert bedrock — Wrong. Wind can erode rock in dry regions, so it can seem like a canyon-maker. But most major deep canyons form when rivers cut downward through uplifted rock, not when wind scours a channel. Wind erosion is real, yet the deep, narrow canyon shape comes from river downcutting.

Glaciers gouge deep troughs that remain after the ice melts — Wrong. Glaciers are powerful erosive agents, so it is understandable to link them with deep valleys. But glaciers usually gouge broad U-shaped valleys, while deep, narrow canyons are made by river downcutting. A glacial trough has a U-shaped cross-section, not the V-shaped cross-section of a river canyon.

Rivers cut downward into bedrock as the land slowly rises ✓ — Correct! Deep, narrow canyons usually form when a river cuts downward into bedrock while the land is slowly uplifted. The Grand Canyon is the classic example: the Colorado River eroded through sedimentary rock over millions of years. Downcutting goes faster when the land rises or sea level drops, and softer rock erodes faster, leaving stepped canyon walls.