It is proposed to construct a new road bridge across Spencer Gulf at Port Augusta, on an alignment south of the existing Great Western Road Bridge. Geological investigations, mainly cable-tool have shown up to 95 ft of sediments of Tertiary to Recent age, in a downfaulted trough, overlying bedrock of Proterozoic (Marinoan) Age. There are no geological problems likely to affect the feasibility of the project. There is no advantage geologically in any other alignment than the one adopted. Medium dense to very dense sands and clayey sands overlying siltstone and sandstone materials would provide refusal to most types of driven piles. No evidence of any major faults or any recently active minor faults has been found in the area. However, the site lies within a broad zone of faults along which minor movements have occurred in historical times and the possibility of an earthquake up to intensity 8 on the modified Mercalli Scale should be allowed for in the design.