Marking a high elevation point to determine the watershed edge is not a typical practice. Instead, watershed boundaries are typically determined by following topographic features, specifically the divide line, which is the ridge or crest that separates different drainage basins.

Here's why:

* Water flows downhill: Watersheds are defined by the direction water flows. Water naturally flows downhill, following the slope of the terrain.

* Divides separate drainage: The divide line marks the point where water will flow in opposite directions, defining the boundary between two watersheds.

* Elevation is not the sole factor: While elevation is important in determining the overall landscape, it doesn't directly define the watershed edge. Two points at the same elevation could be in different watersheds if they are on opposite sides of a divide.

Determining a watershed edge typically involves:

1. Mapping topographic features: Using topographic maps, aerial photos, or digital elevation models (DEMs).

2. Identifying divide lines: Pinpointing the ridge lines that separate the flow of water.

3. Tracing the boundaries: Following the divide lines along the terrain to define the watershed boundary.

In summary, while elevation is a factor in determining the overall landscape, it is not the primary factor in defining a watershed edge. The divide line, which separates drainage patterns, is the key element in determining a watershed's boundaries.