Here's how it forms:

* Glaciers carve out valleys: As glaciers move, they erode the land, carving out a distinctive U-shape.

* Steep sides and a flat bottom: The sides of the valley are steep, and the bottom is relatively flat, unlike the V-shaped valleys formed by rivers.

* Examples: Many valleys in mountainous regions around the world are U-shaped, like the Yosemite Valley in California.