Keyline design

Valleys start or head where a portion of a slope near the top of a watershed or divide becomes steeper than the general slope on either side. Thus the first part of a valley formation is steeper than the ridges or shoulders on each side that form the valley. At some point down the valley--the Keypoint--the valley slope flattens to such an extent that it becomes flatter than the ridges or shoulders on each side in the same vertical interval.