karoo koppies hills are capped by hard, erosion-resistant dolerite sills. this is solidified lava that was forced under high pressure between the horizontal strata of the sedimentary rocks that make up most of the karoo’s geology. this occurred about 180 million years ago, when huge volumes of lava were extruded over most of southern africa and adjoining regions of gondwana, both on the surface and deep below the surface between the sedimentary strata. since this massive extrusion of lava, southern africa has undergone a prolonged period of erosion, exposing the older, softer rocks, except where they were protected by a cap of dolerite. the genera present include: