 The Wianamatta Plain, with many undulating hills of Wianamatta Group shales and sandstones, bounded by the Woronora and Illawarra Plateaus to the south, the Blue Mountains Plateau to the west and the Hornsby Plateau to the north/northeast.At the front of the Blue Mountains Plateau runs the Lapstone Structural Complex, which forms the western edge of the Cumberland Basin and Cumberland Plain.This is a north-south trending collection of reverse faults and monoclinal folds which extends generally north south for over .