 It is called the Reading Prong by geologists.The name South Mountain is applied to the southernmost cluster of peaks in the feature, straddling Berks, Lancaster, and Lebanon counties; and also to the northernmost end of the feature as the ridge into which Lehigh University is built.South Mountain borders Emmaus, just to the south of Allentown, and comprises a ridge of low mountains passing east of Reading and then extending nearly due west.