PIRACY

"Elbow of capture just upstream of the bedrock high"

  Often times, but not always, the pirated drainage develops a sharp course alteration just upstream of the point of capture.  Unfortunately, overflow transverse drainages can also develop this feature.  For this reason, drainages that exhibit an elbow upstream of the bedrock high implies piracy, but to elevate a piracy hypothesis beyond speculation, further evidence is needed.  The upper image illustrates an elbow of capture from a physical model  and the lower image provides a field example from Organ Pipe National Monument.