 It is also noted for historic stone-pitched overshot weirs (causeways) built by Chinese labourers in 1883.Combo Waterhole lies at the northern rim of a roughly circular zone measuring some 130 km across that has been identified by Geoscience Australia as a crustal anomaly.Proof is currently lacking as to the cause, but it is believed likely that the anomaly was caused by an asteroid strike that happened about 300 million years ago.