Earth Camp Living Over Caves in Austin Nico M. Hauwert, Hydrogeologist and Susan Wall, Education Coordinator City of Austin Watershed Protection and Development Review Department This is what Austin looked like 75 million years ago. Georgetown Clam 75 million years ago there were about 10 volcanoes in Austin. Calcite Mineral Makes Up Limestone Rock Dissolution of Limestone Rock Karst Aquifer Creekwater Disappearing into Dry Fork Sink on Tributary of Williamson Creek Whirlpool in Onion Creek