The Chehalis basin is one of the most diverse watersheds in the state, with major tributaries draining the Willapa Hills to the west, the Cascade foothills to the east, glacial prairies to the northeast, and the Olympic Mountains to the north. It is the largest basin in Washington State outside of the Columbia basin, and drains over 2660 square miles.
The Chehalis River Basin:
- drains 2,660 square miles of land
- major population centers are Chehalis, Centralia, Aberdeen and Hoquiam
- has eight (8) major sub-basins
- each sub-basin has a number of creeks, anywhere fro – m 2 to 12
- sub-basin problems identified in 1996 include dissolved oxygen, high water temperatures, fecal coliform, and PCBs
Much of the basin is covered by commercial forest, with development concentrated in the lower valleys. Most of the area is too low to maintain a winter snowpack, so flooding usually comes from late fall/early winter rainstorms. The lack of a winter snowpack also means summer flows are often very low, depending on water stored in the ground after the rainy season ends.
Geology of the Chehalis River Basin
The mainstem Chehalis starts where the East and West Forks meet near Pe Ell in the Willapa Hills. These forks cut canyons into siltstones, sandstones, and basalt that were once on the Pacific Ocean floor. Crabs, whalebones, and other marine fossils are often found in the stream bed here.
The river then flows east towards Chehalis and passes over Rainbow Falls. These falls are made up of volcanic basalts that flowed into the Chehalis Basin from the massive volcanoes that also created the Columbia plateau in eastern Washington.
These 175 acres include high quality coastal surge plain lands and six miles of sloughs at the head of Grays Harbor, in Grays Harbor County. The site will be known as the Elliot Slough parcel, and is part of a larger effort to conserve the Chehalis River Surge Plain and is located near to a State Natural Area Preserve and an Audubon Society preserve.
These tidal lands are home to salmon, deer, and a great variety of birds. With spruce, willow, crabapple, cattails and many more wetland plants, this western end of the Chehalis River surge-plain possesses huge ecological value. This habitat type is often called the “nursery of the sea” because a huge number of valuable marine species begin their lives in quiet, shallow estuaries.
In the future, CRBLT plans to offer birding with the Grays Harbor Audubon Society and botany field trips to Chehalis Basin Schools. The Center for Natural Lands Management is already under contract to remove the small patches of knotweed in one area of the wetlands. Overall, this large wetland complex is chock-full of healthy, native plants and wildlife who thrive in a very wet, tidally influenced environment like we have here.