A system of parallel arcuate ridges dominates the topography of the Billa Kalina area; facies relationships indicate that they are silicified strandlines of a Miocene lake which have been etched out by later erosion. Clays and dolomites of the Miocene Etadunna Formation were deposited in the distal portion of the lake, which at its peak was over 100 km wide. An initially wet climate was replaced by increased aridity, culminating in evaporitic conditions. Climatic deterioration initiated regression of the lake shoreline, which is recorded by upward coarsening sequences. In the east, the lake had contracted for large distances over an essentially flat land surface, in contrast to in its the north and west, where a higher, steeper terrain limited regression. During still-stands, shorelines were foci of silica and calcite cementation from laterally moving groundwaters; there is evidence of penecontemporaneous reworking of silica and calcite - cemented sediments. To the north and west of the lake, coarse-grained terrestrial sediments of the Mount Sarah Sandstone were deposited. These rocks are strongly silicified to 'grey billy' silcrete, and correlate with similar silcreted sandstones intertonguing with the Etadunna Formation. The main silcrete of the Billa Kalina area is late Tertiary in age, and is unrelated to a deep weathering profile developed in underlying sediments.