Recent excavations at Mangalo (Fig. 1), in connection with extensions to a silo complex, have revealed unusual foundation conditions that were not anticipated in the original site investigation. The geological section, exposed in the main foundation trench, clearly shows the relationship of several Quaternary units with weathered Cleve Metamorphics, which form bedrock beneath the area. 1 The site lies on the crest of a low rise which drops gently down to Salt Creek about 0.5 km to the south east. Fresh strong gneiss and schist crops out in the creek and on the flanks of the rising ground towards the site. A site investigation for the first silos, (Steel, 1964) showed fresh strong bedrock at from 1 to 1.5 m below ground in two cable tool holes. A third hole encountered weathered clayey gneiss extending to 3 m before fresh rock was proven, but indications were that the weathered material was of very limited distribution and reasonably stiff. During the construction of an additional group of silos in June, 1977, excavations for the foundation trench at the eastern end of the site, revealed several metres of clay and gravel passing down to a stiff red clay. As a result of this, the fotting design was changed to reduce the load on the foundation in this area.