Mountain valleys are low areas of land situated between mountains or hills. They are often formed by the erosion of rock and soil over time, typically through the action of rivers or glaciers. These valleys can vary in size and shape, and they often feature lush vegetation and diverse wildlife due to the availability of water and fertile soil. Many mountain valleys are home to rivers, lakes, and streams, which provide essential resources for both ecosystems and human activities. Popular examples of mountain valleys include the Yosemite Valley in California and the Great Valley in Pennsylvania. These areas are often popular for outdoor activities such as hiking, camping, and fishing.