The drawing above illustrates a five-step process of gully movement.

Step 1: Runoff moves surface soil downslope from bedrock.

Step 2: A small headcut forms at a weak point in the soil surface downhill from a bedrock and in the runoff.

Step 3: Falling water cuts the headcut farther up hill and deeper.

Step 4: The headcut will continue to deepen and move uphill until it reaches the top of the hill or a nonerodible point such as three roots or rock.

Step 5: Grass and shrubs begin to grow in gully as it stabilizes. Bedrock uphill stabilizes the headcut.