The Peake and Denison Ranges comprise four northerly trending Precambrian inliers in the southwestern portion of the Great Artesian Basin. The Peake Metamorphics (?Early Proterozoic), the oldest rocks exposed, are composed of interlayered meta basalts and quartzites, in sequences over 10 000 m thick. These rocks were subjected to greenschist to amphibolite facies metamorphism and syntectonic granite intrusion about 1650 Ma, and fu rther deformation and probable greenschist facies metamorphism at 1050 Ma. Unconformably overlying the Peake Metamorphics there are at least 29 000 m of Adelaidean paralic sediments deposited in a steadily subsiding, fault-bounded trough which was a northern extension of the Adelaide Geosyncline. The thickness (27000 m) of Willouran and Torrensian sediments preserved here is greater than elsewhere in the geosyncline. Adelaidean sedimentation is first recorded by the Willouran Callanna Beds: a basal clastic sequence (Young husband Conglomerate) is overlain by the stromatolitic Coominaree Dolomite and the predominantly basaltic Cadlareena Volcanics. Faulting and diapirism have caused extensive disruption of the sequence above the Cadlareena Volcanics. From this dismembered succession the following stratigraphic units of Willouran or Torrensian age have been recognised: Rockwater Beds, War Loan Beds, Nilpinna Beds, Duff Creek Beds, and Murrana Beds. The overlying Torrensian sequence (Burra Group) exceeds 10 000 m and comprises: unnamed siltstones, Fountain Spring Beds, Mount Margaret Quartzite, Skillogalee Dolomite, unnamed transition unit, and Kalachalpa Formation. A period of mild erosion preceded deposition of the Sturtian-Marinoan Umberatana Group. The onset of glacial conditions resulted in deposition of the glaciomarine Calthorinna Tillite and interfingering sandstones. Subsequent marine silty shales and silty dolomites of the Tapley Hill r'ormation are overlain by the regressive Thora Dolomite and Willochra Subgroup. Folding, diapirism, and metamorphism (to low greenschist facies) of the Adelaidean succession during the Cambro-Ordovician Delamerian Orogeny was accompanied by late-tectonic intrusion of porphyritic monzonites, syenites, diorites and albitites (Bungadillina Monzonite).