Willamette Floodplain National Natural Landmark

Ice Age Floods National Geologic Trail

The Willamette Floodplain represents the mix of bottom-land grasslands once common throughout the interior valleys of western Oregon and Washington.

It is a large remnant example of largely un-plowed native grassland and ash woodland.

The bottom-land grasslands include the largest remnants in the North Pacific Border Region.

These grasslands include both the full range of bottom-land communities and the large diversity of endemic species primarily restricted to these habitats.

The grassland communities include a fairly complex matrix of tufted hair grass bottom-land prairie (Deschampsia caespitosa valley prairie), sedge-meadow barley bottom-land grassland (Carex unilateralis – Hordeum branchyantherum bottomland grassland), and hawthorn- rose bottom-land shrub-land (Crataegus douglasii – Rosa nutkana bottomland shrub-land), all of which are well represented at the site in areas with pluvial clay or silty clay soils.

In the better drained areas, where alluvial silt loams occur, a matrix of tufted hair grass valley prairie and red fescue valley prairie (Danthonia californica – Festuca rubra valley grassland) is found.

In the very wet area along Muddy Creek are large and significant examples of Oregon ash bottom-land forests (Fraxinus latifolia/Carex obnupta and Fraxinus latifolia/Symphoricarpos albus).

All of these grassland and shrub-land communities have become increasingly rare as most of the bottom-land areas in the interior valleys have been converted to farmland and to pasture.

In the bottom-land grassland are found five vascular plant species listed by the U.S. Fish and Wildlife Service as candidate threatened or endangered species.

The site also has populations of some threatened and endangered animal species.

The area has occurrences of two threatened animals of concern to the U.S. Fish and Wildlife Service.

Muddy Creek has populations of the Oregon Chub (Hybopsis crameri), a candidate species endemic to the Willamette and Umpqua River systems.

The site has wintering populations of Lewis’ Woodpecker (Melanerpes lewis) and breeding Western Pond Turtles (Clemmys marmorata), both of which are considered threatened in Oregon but more common elsewhere.

The site is located on essentially flat topography typical of the floor of the Willamette Valley.

It is on the Calapooyia geomorphic surface, characterized by the absence of appreciable local relief.

Elevation ranges from about 270 to 290 feet (82 to 88 meters).

Gentle swales and ridges, which are most easily distinguished on aerial photographs, provide the only variation.

Muddy Creek, a small, turbid, meandering, valley-bottom stream with associated ash forests, flows along the eastern edge of the area.