Geological mapping shows that the reservoir area consists of Torrensian siltstones, dolomites and quartzites. These are strongly jointed with a pronounced slaty cleavage. The joints form three distinct sets. The geological structure is of uniformly dipping beds with numerous faults, one of which passes through the left abutment of the dam site. This fault appears to be of Cambrian-Ordovician age and is probably inactive. No significant leakage from the reservoir area is expected. Numerous small scale soil slips together with evidence of rock mass disturbance on the right back upstream of the dam site indicate that stability problems may occur during reservoir filling.