The Peake and Denison Ranges comprise four northerly-trending Precambrian inliers in the south-western portion of the Great Artesian Basin. The Peake Metamorphics (?Lower Proterozoic), the oldest rocks exposed, form inliers of interlayered metabasalts and quartzites, in sequences over 10,000 m thick. These rocks were subjected to greenschist through to amphibolite facies metamorphism, and to syntectonic granite intrusion, at about 1600 Ma, and further deformation and probable greenschist facies metamorphism at 1050 Ma. Unconformably overlying the Peake Metamorphics are at least 20,000 m of Adelaidean paralic sediments deposited in a steadily subsiding, fault-bounded trough which was a northern extension of the Adelaide Geosyncline. The thickness (27,000 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 conglomerate-quartzite (Younghusband Conglomerate) is overlain by the stromatolitic Coominaree Dolomite and the predominately basaltic Cadlareena Volcanics. Faulting and diapirism have caused extensive disruption of the sequence above the Cadlareena Volcanics. From the 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) thickness exceeds 10,000 m, and comprises: unnamed siltstones, Fountain Spring Beds, Mount Margaret Quartzite, Skillogalee Dollomite, unnamed transition unit, and Kalachalpa Formation. A period of mild erosion preceeded deposition of the Sturtian 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 Formation are overlain by the regressive Thora Dolomite and Willochra Subgroup. Folding, diapirism and metamorphism (to lower greenschist facies) of the Adelaidean succession during the Cambro-Ordovician Delamerian Orogeny were accompanied by late-tectonic intrusion of porphyritic monzonites, syenites, diorites and albitities (Bungadillina Monzonite).