SEDIMENTARY ROCKS OF SOUTH MOUNTAIN 203 



From the Potomac to the Maryland- Pennsylvania state hne 

 the mountain has approximately a straight, unbroken course nearly 

 due north. At the East Branch of Little Antietam Creek, in the 

 southeast corner of the area shown on the accompanying map, 

 there is an offset of the mountain front of about one mile westward, 

 the ridges on the north side lying farther into the valley. A short 

 distance to the north another offset into the valley, of about 2| miles, 

 is produced by the sharp bend of the ridges to the westward, beyond 

 which they again assume their northeasterly course, as may be 

 seen on the map. North of Conococheague Creek another offset 

 of 3^ miles is produced by the development to the westward of another 

 ridge, broad and flat-topped, and dissected by numerous deep lateral 

 valleys. This Big Flat Ridge has an altitude of over 2,100 feet, 

 the highest point of South Mountain in Pennsylvania. 



The drainage of the mountain area is accomplished by the East 

 Branch of Little Antietam Creek and Conococheague Creek and 

 their tributaries. The former rises some distance east of the area 

 represented on the map, and flows southwestward directly across 

 the ends of the ridges on the north side of its valley, but nearly 

 parallel to the ridges on the south side. Its tributaries are all 

 short, and form longitudinal valleys between the ridges on the north. 

 The West Branch of Little Antietam Creek drains a portion of the 

 Cumberland Valley adjacent to the mountains, and has its head- 

 waters in the short longitudinal valley which outlets at the gap east 

 of Montalto. 



Conococheague Creek heads far beyond the border of the mapped 

 area, and, after flowing southwestward in a longitudinal valley, 

 turns abruptly westward through a gap in the ridges. It has several 

 large tributaries which drain the interior of the mountain area in 

 this vicinity, chief of which are Newmans Branch, a transverse 

 stream from the east, and Rocky Mountain Creek, a longitudinal 

 stream from the south. Numerous short tributaries head in the 

 deep ravines on the east flank of Big Flat Ridge. Others on the 

 west side of the ridge find underground courses beneath the cover- 

 ing of wash on the surface, or sink into limestone caverns before 

 they reach the main stream. The waters of both Conococheague 

 and Little Antietam creeks ultimately reach the Potomac River 

 to the south. 



