Palouse Loess

August 30, 2010

Palouse loess
: Stu Witmer
Summary Author: Stu Witmer

In the Pacific Northwest about 17 million years ago, shield volcanoes produced great cracks in the Earth. For about 10 million years these cracks oozed copious amounts of lava which ultimately covered more than 60,000 square miles (155,400 sq km) with 6,000 feet (1,830 m) of basaltic lava. Time passed and the lava cooled to rock. About a million years ago, during the Pleistocene epoch, things got really cold and huge glaciers formed. Soil and silt, partly volcanic in origin, was blown by the winds off the glaciers, much of it landing on the almost horizontal basalt plateau. During the last glacial period, about 15 thousand years ago, this loose, airborne soil accumulated to a depth of over 200 feet (60 m) in some places. The area receives about 20 inches (51 cm) of moisture annually and hosted a variety of grasses along with wild roses and the edible common snowberry. The loess is also home to the Giant Palouse earthworm.

Today this region is called the Palouse and the distinctive deep, rich soil is known as Palouse Loess. The photo above is a typical roadcut in Southeastern Washington showing the depth, color and stratification of the Palouse loess. The word Palouse may be a reference to the local Native American tribe, or it may have an older French origin. Loess is a German word meaning loose. It was first applied to the soil type along the Rhine River. When European farmers first came to the Palouse the loess was thought to be too arid for farming and was considered part of the Great American Desert. Some experiments in dryland farming of wheat began as early as the 1840s. About 20 years later the first threshing machine arrived followed by other technology including, in the 1870s, the first railroad. All of these developments aided the production and distribution of crops. In recent years Washington has generally produced a higher yield per acre of wheat than any other state, and in 2009 produced over 120 million bushels. Other crops grown in the Palouse include barley, peas and lentils. Agriculture has been such a success that by the 1970s the major stands of native plants were gone. Several restoration projects are underway. Photo taken May 2010.

Photo Details: Camera: NIKON E5700; Focal Length: 14.7mm (35mm equivalent: 58mm); Aperture: f/5.0; Exposure Time: 0.0037 s (1/267); ISO equiv: 200; Exposure Bias: none; Metering Mode: Spot; Exposure: program (Auto); White Balance: Auto; Flash Fired: No; Color Space: sRGB.