The Spalding inlier is a lens-shaped area of tightly-folded Willouran rocks of the Adelaide System (Upper Precambrian), extending north-south for about 10 miles; it is about 100 miles north of Adelaide. The rim of the inlier is marked in most places by a faulted junction with the Rhynie Sandstone which is repeated by extensive inferred north-south thrusts on the western limb of the structure. The inlier forms the core of an overturned anticline with an axial surface dipping about 70 degrees west. The core rocks, siltstones and dolomites probably of the River Wakefield Group, are intruded by small plug-and-sill-like masses of basic igneous rocks, some of which may be Willouran in age; there are a few small associated copper shows. Overlying the Rhynie Sandstone east and west of the inlier are other formations of the Burra Group of the Adelaide System in normal sequence.