GEOMORPHIC AND PEDOLOGIC ORIGINS OF THE ROOSTER ROCK DUNE, OREGON

 

A large longitudinal landform rises above the south bank of the Columbia River at Rooster Rock State Park.  This east-west trending landform is located 35 km east of Portland (45°32’57” N, 120°14’10” W) and is approximately 1500 meters long, 500 meters wide, and rises 50 meters above the surrounding landscape.  A soil catena study was performed to determine its age and geomorphic origin based on its soil development.  Four soil pits were dug in a north-south transect on the north side of the ridge, and one pit was completed on the south-facing slope.

 

The landform is young in age, less than 500 years, based on its minimal soil development in all five pits (A-C profiles).  All the soils have similar characteristics, regardless of their location on the catena and are classified as Typic Udipsamments.  A grain size analysis determined the well-sorted population to be medium to fine grained sand with typical mineralogy of Columbia River sediments.  Based on the well sorted nature of the sand, we conclude that the origin of the landform is eolian and therefore a dune.  This dune is an active landform and sediment will continue to accumulate if current climactic conditions persist.