Five stratigraphic bores at Chowilla Dam Site intersected Post-Tertiary river sands and silts, equivalents of the Loxton Sands grading downwards into highly glauconitic siltstone of the Bookpurnong Beds and, in two bores, Shelly glauconitic marls, clay, and siltstone equivalent to the Pata Limestone. Sedimentation was continuous from the time of deposition of the Pata Limestone (Middle Miocene) to the end of the Miocene or early Pliocene when deposition of the Loxton Sands took place. The sediments intersected give further evidence of the retreat of the sea in a south-south-easterly direction at the end of the Miocene and of the presence during the Upper Miocene -Lower Pliocene of salt swamps in this part of the Murray Basin. Only the uppermost part of the Murray Basin sequence was intersected. It is comparable with that above 200 feet in Canopus No. 1 Bore.