One reason is that within this stretch, the streambed slope is steep, measured at a 6% grade. This is four to six times steeper than any other reach of the San Pablo after the stream leaves the mountain. With a steeper slope, the water has more erosive power.
The second reason is that this zone includes headcuts and log structures. The owner of this 4-acre parcel of land agreed that establishing a zone where livestock were permanently excluded would allow willows, sedges, grasses and other vegetation to return and thrive. The vegetation enables the streambed to endure seasonal flash floods with little to no erosion.