Its watershed drains a portion of the Cascade Range east and northeast of Mount Rainier, including parts of the Norse Peak Wilderness.

The Greenwater River defines part of the boundary between King and Pierce counties.

The Greenwater River rises in eastern Pierce County, in the Norse Peaks Wilderness near Corral Pass.

Along with a few headwater tributaries, it drains the north side of Castle Mountain.

The boundary between King and Pierce counties follows Meadow Creek down from Naches Pass.