North of Media (Delaware County, PA) Crum Creek and Ridley Creek flow in closely spaced southeast oriented valleys and then turn to flow in south-southeast oriented valley. Geist Reservoir is an artificial lake flooding a Crum Creek valley segment. Both Crum Creek and Ridley Creek in this region are joined by northeast and north-northeast oriented barbed tributaries. Further saddles or shallow through valleys mark low points on the narrow Crum Creek-Ridley Creek drainage divide and link short northeast and north-northeast oriented Crum Creek tributary valleys with short southwest and south-southwest oriented Ridley Creek tributary valleys and provide evidence of flow routes that existed prior to the erosion of the deeper Crum Creek and Ridley Creek valleys.

Figure 1: Crum Creek-Ridley Creek drainage divide area near Geist Reservoir. United States Geological Survey map digitally presented using National Geographic TOPO software.

Figure 1 illustrates the Crum Creek-Ridley Creek drainage divide area near Geist Reservoir. Geist Reservoir floods the Crum Creek valley and Crum Creek flows from Geist Reservoir in a south direction to the southeast corner of figure 1. Ridley Creek flows from the northwest corner of figure 1 in a southeast and south-southeast direction to the south center edge of figure 1. Media is the town at the southeast corner of figure 1 and is located on the divide between Crum Creek and Ridley Creek just south of the southeast quadrant of figure 1. The numbers 1, 2, and 3 identify saddles or shallow through valleys crossing the Crum Creek-Ridley Creek drainage divide. Note how those saddles or shallow through valleys link short northeast or north-northeast oriented Crum Creek tributary valleys with short southwest or south-southwest oriented Ridley Creek tributary valleys. The number 4 identifies Dismal Run, which is a north-northeast oriented barbed tributary draining to south-southeast oriented Ridley Creek. While not labeled note the north-northeast oriented Dismal Run tributary and other northeast and north-northeast oriented Ridley Creek and Crum Creek barbed tributaries.

The saddles or shallow through valleys and barbed tributaries provide evidence of water flow routes that existed prior to headward erosion of the much deeper Ridley Creek and Crum Creek valleys. Evidence seen in figure 1 suggests at least three and possibly several more southwest or south-southwest oriented flow routes crossed the region and were captured by headward erosion of the deeper Ridley Creek valley and subsequently by headward erosion of the deeper Crum Creek valley. These multiple and parallel former southwest and south-southwest oriented flow routes suggest the region was crossed by massive and prolonged southwest and south-southwest oriented flood flow at the time the deep Ridley Creek and Crum Creek valleys eroded headward into the region. The floodwater source cannot be determined from southeast Pennsylvania evidence, but may have been melt water from a continental ice sheet, although previously published interpretations suggest southeast Pennsylvania region drainage networks