Quarrying companies gradually took over more and more of Prospect Hill, mining the dolerite for use as roadstone until it was almost all gone and much of the hill with it. The Prospect quarry, which is now part of Pemulwuy, is formed by an intrusion of dolerite rock into Ashfield Shale. At least seven different rock types occur in the intrusion. The material is predominantly coarse grained picrite with olivine-dolerite and dolerite. Quarrying in the area last occurred in 2007. In the early 2010s, the 330ha quarry gap was transformed into light industry area. Prospect Highway now winds through the gap.