Glacial valleys are U-shaped valleys formed by the movement of glaciers over time. As glaciers advance, they carve out the landscape, creating wide, flat bottoms and steep sides. This process can take thousands of years, resulting in distinct geological features. These valleys are often found in mountainous regions and can be filled with water, forming lakes. The Yosemite Valley in California is a well-known example of a glacial valley, showcasing the dramatic effects of glacial erosion. Glacial valleys are important for understanding Earth's geological history and the impact of climate change on landscapes.