Grays Harbor is approximately 15 miles long and 13 miles wide and can be described as boot-shaped with the toe being the mouth of the Chehalis River. This figure includes the Grays Harbor, Westport, and Grayland areas. The two largest rivers within this subbasin that empty directly into Grays Harbor are Johns River, draining a 32 square mile area and the Elk River, which has an 18 square mile drainage. These rivers drain forested areas. In the Lower Chehalis Subbasin, the surrounding land is characterized by a broad and flat valley floor, with the river flowing near its southern edge.
Steep hills rise from the river on the southern side.
On the northern side the valley blends with tributary valleys or rises in gentle to steep hills. Soils Soils in the subbasin range from deep to very deep. On the hillsides and in the upstream portions of the lower Chehalis subbasin soils are well-drained. In the downstream portions and in the estuary they range from well drained to poorly drained. During periods of high water in the winter much of the floodplain is covered with water .