The Frome 1: 250 000 map covers the northern part of the South Australian portion of the Frome Embayment. The embayment is essentially the eastern portion of a Mesozoic basin, developed on Palaeozoic and Precambrian rocks during Upper Jurassic time by gentle down warping and faulting. It is an extension of the Great Artesian Basin, and contains marginal and shallow marine Cretaceous sediments, veneered by fluviatile and lacustrine (possibly estuarine) Tertiary sediments, and fluviatile, lacustrine and Aeolian Quaternary sediments. The Cainozoic sediments occupy a shallow basin, and are faulted against the Adelaide Geosyncline rocks of the Flinders Ranges to the west. To the east they thin over a broad arch, which develops into a well-defined ridge to the south. This ridge was also a positive area during Mesozoic sedimentation, and constitutes Willyama Complex metamorphic and granitic rocks and porphyritic rhyolite of unknown age. Middle Cambrian rocks, folded into simple open structures, exist beneath the Mesozoic strata over a large areas of the southern portion of the Frome Embayment. It is thought that the area formed a stable craton during Palaeozoic time. The climate in the Tertiary was sub-tropical to tropical in Paleocene times with high rainfall, and the surrounding terrain had high relief, the temperature dropped slightly during the Eocene. The Middle Miocene had a strongly seasonal sub-tropical climate with (initially) high rainfall and relief was low. There is also evidence for arid periods. The period from late Miocene to Lower Pleistocene is ill-defined, and it was during this time that the Flinders Ranges were rapidly uplifted. A semi-arid climate prevailed. Late Pleistocene climate was initially wet, but later became more arid, and Lake Frome probably approached its present dimensions during Plio-Pleistocene times. The Tertiary Namba Formation and Eyre Formation contain significant uranium deposits of the geochemical cell type. Extensive deposits of swelling clays are present on the central south margin of the sheet. The major utilized resource is water, drawn from three major aquifers: the basal Cretaceous, the Tertiary sands, and conglomerates and sands of the Willawortina Formation. In general Cainozoic sediments are the present aquifer west of Lake Frome, and Mesozoic sediments to the east.