The Willamette Floodplain consists of 713 acres (289 ha) of natural grassland that was made a National Natural Landmark near the Willamette River in May 1987.[1] The floodplain is within the William L. Finley National Wildlife Refuge and located about 15 miles (24 km) south of Corvallis in Benton County, Oregon, near Willamette RM 150.
It is the largest remaining native unplowed example of bottomland interior valley grassland in the North Pacific Border natural region. It was classified as a natural landmark because such grassland and shrubland areas are exceedingly rare, with most having been cultivated or turned into pastureland.
The Long Tom River joins the Willamette in the area. There are numerous meanders, many disconnected from the Willamette. The Irish Bend Covered Bridge crosses one of them.