Natural, isolated, relict artesian springs found in arid, outback Queensland and South Australia. Water stored in deep aquifers seeps to the surface through fault lines in the rock, and the sediments and salts within the spring water form elevated mounds as it evaporates. Most such springs support marginal plant growth that help stabilise the sediment and provide shelter for animals. In South Australia mound springs form an arc of about 400km along the south-western edge of the Great Artesian Basin, although many have disappeared in the last 100 years as a result of water extraction.