Geologically, the area consists of alluvial sediment and volcanic flows originating from now-extinct volcanoes such as nearby Buninyong (750m, 2460ft) and Warrenheip (746m, 2446ft), which are the area's tallest peaks. As a result, the basin contains large areas of fertile agricultural soil. Ballarat itself is situated on an alluvial basin of the Yarrowee catchment and its tributary creeks, penetrated by sub-ranges of schists composed of granites and quartz. Along with the visible river and creeks, the catchment basin has numerous active and inactive aquifers and natural wetlands, which are used for urban water supply, agriculture and recreation.