South Mountain (eastern Pennsylvania)

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South Mountain is colloquial name applied to features in the mountain range extending south and south west from the Lehigh Valley region of Pennsylvania. At times, it also been known as Durham Hills, Reading Hills, and the Lehigh Mountains. It is called the Reading Prong by geologists. Interestingly, the name South Mountain is applied to the southern most cluster of peaks in the feature, straddling Berks, Lancaster, and Lebanon counties; and also to the northern most end of the feature as the ridge into which Lehigh University is built.

South Mountain borders Emmaus, Pennsylvania, just to the south of Allentown, Pennsylvania, and comprises a ridge of low mountains passing east of Reading, Pennsylvania and then extending nearly due west. It is a continuation of the New England Province and is the southern end of the Hudson Highlands^[1].

The ridge does not follow a straight line like Blue Mountain, located to the north.

South Mountain ranges in elevation between 500 and 1,300 feet above sea level. The ridge is made of metamorphic rocks and gneiss, which date to the Precambrian era and range from about 570 to 1,600 million years old.

South Mountain is largely undeveloped in its northern extension due to conservation efforts and its steep slope. This makes it a beautiful backdrop to the viewpoints of the Lehigh Valley, including, at night, the city lights of Allentown. The southern end of this feature extends west along Pennsylvania route 422 and the southeastern border of Berks County, providing views of Blue Mountain (to the north), Mount Penn (which comprises part of the prong), and the city of Reading, to the east. The southern most peaks were at one time home to many exclusive sanitariums and resorts, now all defunct.