[4] The river was altered by the 1980 eruption of Mount St. Helens, a nearby volcano, and subsequent flows of ash and other debris.

[4] The Toutle River then turns west, passing under Tower Road and receiving Cline Creek from the right.

Over its final 4 miles (6 km), the Toutle meanders generally southwest through large deposits of sand.

The stream passes under Barnes Drive and then Interstate 5 before entering the Cowlitz River about 2 miles (3 km) upstream from the city of Castle Rock.

[4] The United States Geological Survey monitors the flow of the Toutle River at a stream gauge at RM 6.5 (RK 10.5).