Variant names, according to the United States Geological Survey (USGS), include Hum-tu-lups, Humptolups, Humtutup, and Um-ta-lah.

This region of Olympic Peninsula receives around 220 inches (5,600 mm) of precipitation annually, feeding many streams.

Flowing south and southwest, the forks exit the mountains, merging about 4.5 miles (7.2 km) above the town of Humptulips.

After the hatchery, the river turns south, flowing the last few miles before its mouth at North Bay of Grays Harbor, which empties into the Pacific Ocean.

The nearest cities are Hoquiam and Aberdeen, located at the mouth of the Chehalis River on Grays Harbor.