Figure 1: Jericho Mountain in Bucks County, PA. Bowman Hill is located north of the Jericho Mountain northeast end. The Delaware River flows in a southeast direction across the figure 1 northeast corner. Jericho Creek flows in an east-southeast and east-northeast direction along the Jericho Mountain south flank. Pidcock Creek drains the area north of Jericho Mountain. United States Geological Survey topographic map digitally presented using National Geographic TOPO software.
Jericho Mountain is a high ridge (more than 440 feet at its highest point while the adjacent Delaware River elevation is approximately 40 feet in figure 1). Jericho Mountain has an arc-like shape being oriented in a west-to-east direction in the west and in a south-to north direction in the east. North of the Jericho Mountain east end is Bowman Hill, which is probably a Jericho Mountain extension of some type. Jericho Mountain and Bowman Hill are composed of erosion resistant bedrock while surrounding regions are underlain by less erosion resistant materials. The Pennsylvania Geological Survey web applications map shows mudstone, shale, and siltstone of Triassic age to be the bedrock underlying regions surrounding Jericho Mountain and Bowman Hill while Jericho Mountain and Bowman Hill are composed of a fine-grained igneous rock known as diabase. The diabase was intruded into the surrounding sedimentary bedrock during the Mesozoic Era. All rocks exposed in the Jericho Mountain area have been tilted and uplifted since their formation and much more recently erosion events lowered the surface surrounding Jericho Mountain and Bowman Hill and created the present day landforms.
Bedrock surrounding Jericho Mountain and Bowman Hill was removed at the time the southeast oriented Delaware River valley eroded headward across the region. Headward erosion of the Delaware River valley into the area occurred when the entire region was at least as high or higher than the present day tops of Jericho Mountain and Bowman Hill. At that time massive and prolonged southwest oriented floods moved across the entire region in anastomosing complexes of shallow diverging and converging channels permitting water to move freely between flood flow channels. The southwest oriented floods were responsible for lowering the landscape surrounding Jericho Mountain and Bowman Hill, but were unable to deeply erode the more erosion resistant bedrock found at Jericho Mountain and Bowman Hill. As a result today Jericho Mountain and Bowman Hill are residuals providing evidence of what was once a much higher-level land surface.
Southwest oriented flood flow channels once crossed Jericho Mountain, but were unable to deeply erode the erosion resistant rock and were then channeled between Bowman Hill and Jericho Mountain and along the Jericho Mountain north and south flanks. Delaware River valley headward erosion beheaded the southern flood flow channels first and those beheaded flood flow channels reversed flow direction to flow in an east direction to reach the much deeper Delaware River valley and to create what is today the Jericho Creek drainage basin. Headward erosion of the deep Delaware River valley next beheaded and reversed the flood flow channel between Jericho Mountain and Bowman Hill and later beheaded and reversed flood flow channels north of Bowman Hill. Reversed flow on those northern channels captured significant flood flow from north of the actively eroding Delaware River valley head and created what is today the Pidcock Creek drainage basin (see Pidcock Creek drainage basin entry on this website for a detailed discussion).