Cave systems represent the most dramatic landforms generated by groundwater.
The world's largest cave, Mammoth Cave, Kentucky, is also one of the prime attractions of the U.S. National Park system. The flow of water through caves also generates one of the most commonly held misconceptions about groundwater. Groundwater is not made up of an network of underground rivers and lakes. Rather, most groundwater is present in billions of tiny spaces between mineral grains or in narrow fractures in bedrock. It helps to keep in mind that caves are relatively rare but groundwater resources are present nearly everywhere across the U.S. Groundwater distribution depends on the porosity and permeability of rocks or sediment.