The volcano Mount Gambier is just one of many geological formations that form the Mount Gambier Volcanic Complex. These include Mount Schank, Mount Napier, Mount Eccles, Tower Hill, Mount Pordon and Mount Rouse which range from being three million years old to five thousand years old. The Mount Gambier Volcanic Complex is a state heritage area. The volcanic complex has maar craters and steam vents which were a result of shallow waters being heated by past volcanic activities. The water that lies in Blue Lake, Valley Lake, Leg of Mutton Lake and Browne's Lake used to be a water table, the upper levels of underground water, that was brought to the surface by volcanic activity.