U-shaped valleys are formed by the erosion of glaciers as they move through mountainous regions. The powerful ice carves out a distinct U shape, characterized by steep sides and a flat bottom. This process occurs over thousands of years, resulting in wide valleys that are often found in areas previously covered by glaciers. These valleys are commonly seen in places like the Alps and the Rocky Mountains. They can also contain features such as glacial lakes and moraines, which are piles of debris left behind by the retreating ice. U-shaped valleys are important indicators of past glacial activity.