Optically stimulated luminescence dating of fluvial deposits

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Although superficially resembling sand or other types of dunes, the loess hills of the Palouse are of far different origin.

Internally, they lack any evidence of cross-bedding or erosion of interbedded layers of loess and calcrete that characterize dunes formed by moving currents.

The simultaneous proliferation of railroads only increased the rapid settlement of the Palouse.

By 1890 nearly all the Palouse lands had been taken up and converted to wheat farming.

Detailed optically stimulated luminescence dating has shown that the uppermost layer of Palouse Loess accumulated between 15,000 years ago and modern times and the layer of loess underlying it accumulated episodically between about 77,000 and 16,000 years ago.

Regional trends in the distribution, thickness, texture, and overall composition of the Palouse Loess indicate that it largely consists of the wind-blown sediments eroded from fine-grained deposits of the Hanford formation that were periodically deposited by repeated Missoula Floods within the Eureka Flats area.

The community of Palouse, Washington, is located in Whitman County, about 7 miles (11 km) west of Potlatch, Idaho.

Nevertheless, the traditional definition of the Palouse region is distinct from the older Walla Walla region south of the Snake River, where dryland farming of wheat was first proved viable in the region in the 1860s.

It is a major agricultural area, primarily producing wheat and legumes.

In addition, the ubiquitous homogenization of the loess by innumerable plant roots and insect burrows as it accumulated further supports the conclusion drawn from numerous thermoluminescence and optically stimulated luminescence dates that individual layers of loess accumulated over an extended period of time in terms of thousands of years.

Finally, the calcrete horzons are paleosols that represent the periodic cessation of loess accumulation for periods of thousands of years during which they formed within the surface of a loess layer.

While this definition of the Palouse remains common today, the term is sometimes used to refer to the entire wheat-growing region, including Walla Walla County, the Camas Prairie of Idaho, the Big Bend region of the central Columbia River Plateau, and other smaller agricultural districts such as Asotin County, Washington, and Umatilla County, Oregon.

This larger definition is used by organizations such as the World Wide Fund for Nature, who define the Palouse Grasslands ecoregion broadly.

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