The Somerton-Huntingdon Valley Through Valley is a shallow west-southwest to east-northeast oriented continuous valley linking the south oriented Poquessing Creek valley (east) with the south oriented Pennypack Creek valley (west). The through valley west-southwest end is drained by Huntingdon Valley Creek, which flows in a south and south-southwest direction before entering the valley. The through valley east-northeast end is drained by an unnamed Poquessing Creek tributary, which flows in a south direction before entering the valley. The drainage divide elevation between these two opposing streams (west of the SEPTA Forest Hills station) is slightly less than 200 feet.
Figure 1: The Somerton-Huntingdon Valley Through Valley extends in an east-northeast direction from the south oriented Pennypack Creek valley (location 4) through the Philadelphia northeast tip at Somerton (location 1) to the south oriented Poquessing Creek valley (location 2). Southwest oriented Huntingdon Valley Creek enters and drains the through valley west-southwest end to Pennypack Creek. A south oriented stream flows from the Forest Hills Cemetery into the valley (west of location 1) and then drains in an east-northeast direction to Poquessing Creek. United States Geological Survey map digitally presented using National Geographic TOPO software.
The SEPTA West Trenton Regional Rail line and Philmont Avenue (Route 63) are located in the through valley, which at Somerton crosses the Philadelphia northeast tip. The Somerton-Huntingdon Valley Through Valley between Poquessing Creek and Pennypack Creek is one segment of a longer through valley used by the SEPTA West Trenton line extending from Jenkintown to east of Neshaminy Falls. The Meadow Brook Through Valley is an extension to the west and links the Pennypack Creek valley with the south oriented Tacony Creek valley. An east extension links the Poquessing Creek valley with a northeast oriented Neshaminy Creek valley segment (with the deep Neshaminy Creek valley then turning to drain in a southeast and south direction). The straightness of this through valley suggests it may have been eroded along a liner geologic feature such as a fault line (the Pennsylvania Geologic Survey web applications map shows a linear boundary between two metamorphic rock units, although both rock units should be equally erosion resistant and are found in erosion resistant ridges on either side of the through valley).
The Somerton-Huntingdon Valley Through Valley is subtle as its south wall today rises only about twenty feet higher than the drainage divide elevation, although the through valley is more evident both to west and east of the drainage divide. The through valley north wall is easy to see and in places rises to more than 300 feet. This evidence suggests the through valley south wall may have been intensely eroded during the through valley formation. If so the erosion occurred during massive and prolonged floods with water spilling out of the through valley in a south direction to flow to what at that time was probably an actively eroding southwest oriented Delaware River valley.
Massive and prolonged southwest oriented floods eroded the Somerton-Huntingdon Valley Through Valley and its eastern and western extensions. Floodwaters initially flowed in diverging and converging southwest oriented channels on a surface higher than the highest elevations north of the through valley today. The deep southwest-oriented Delaware River valley segment (south of the Somerton-Huntingdon Valley Through Valley) eroded headward along one of the major southwest oriented flood flow channels, although numerous other flood flow channels crossed the region now drained by south oriented Delaware River tributaries such as Tacony, Pennypack, Poquessing, and Neshaminy Creeks. Prior to headward erosion of the south-oriented and deep Delaware River tributary valleys the southwest oriented flow helped erode the present day southeast oriented Schuylkill River valley upstream from Philadelphia and south oriented tributary valleys draining to that southeast oriented Schuylkill River segment.
Headward erosion of the deep south-oriented Tacony Creek valley from what at that time was the actively eroding southwest oriented Delaware River valley captured floodwaters moving to the newly eroded Schuylkill River valley in the present day Philadelphia City limits. Just north of present day Jenkintown the deep Tacony Creek valley head eroded headward along a captured west-southwest oriented flood flow channel on the present day Meadow Brook Through Valley, Somerton-Huntingdon Through Valley, and Poquessing Creek-Neshaminy Creek alignment. The straightness of this continuous valley suggests it may have been eroded along a fault line or other linear geologic feature, although it is possible the straightness is simply the result of massive west-southwest oriented flow. In any case the west-southwest oriented flow was next captured by headward erosion of the south oriented Pennypack Creek valley.
Following the Pennypack Creek valley capture headward erosion of the south oriented Poquessing Creek valley then captured the southwest oriented flood flow and reversed flow on the through valley east-northeast end, which captured a south oriented tributary to create the present day south and east-northeast Poquessing Creek tributary draining the Somerton-Huntingdon Through Valley east-northeast end. West-southwest oriented flow to the newly eroded Poquessing Creek valley ended shortly thereafter as headward erosion of the deep south oriented Neshaminy Creek valley captured all regional west-southwest oriented flow.