The Satsop River, with a watershed, rises in the hills and flows south to the Chehalis River. Where the river rises, of annual precipitation qualifies as a temperate rainforest, a term used applied to the Satsop watershed by some publications. The Wynoochee Oxbow meteorological station on the west end of the hills () has both the highest average annual rainfall and the second highest ever recorded in the continental United States. The hills lie partly in the Olympic National Forest but not quite in the Olympic National Park. In a 1916 geological survey, hills in the vicinity of Matlock were included with the Black Hills of Thurston County, but may have been describing formations on the East Fork of the Satsop, to the south of the area described above.