The Streaky Bay and Nuyts 1:250 000 map areas are located on the western side of Eyre Peninsula. Precambrian greenschist and amphibolite facies metamorphics of the Gawler Platform are intruded by Lower Proterozoic or Carpentarian granites, gneisses and gabbro. Sands clays and lignites of possible Tertiary age nonconformably overlie the basement, while in the northeast of the area Hiltaba Granite is probably overlain by Gawler Range Volcanics of Carpentarian age. As well as soils, a mosaic of Aeolian, fluvial lacustrine, shallow marine and transitional Quaternary deposits cover a major part of the area. These units comprise the Semaphore Sand, Molineaux Sand, Woorinen Formation equivalent. Bridgewater Formation, Pooraka Formation, Yamba Formation (gypseous deposits), St. Kilda Formation (silty shell sand), and Glanville Formation (Anadara - bearing calcreted shelly limestone). Soil B horizons consist of the Loveday Soil and various calcretes including the calcrete in Bakara Soil and the Ripon Calcrete.