What makes up the soil of the Palouse hills region and how was it deposited?

Loess or silt blown by wind makes up the soil of the Palouse hills region. Palouse is actually a region that is present in the north western part of United states of America. It encompasses a huge area that includes north and central Idaho and southeastern Washington. This is a very fertile region in regards to cultivating Legumes and Wheat. At its thickest place the Palouse is about 75 meters thick. Although the silt blown by the wind may look sandy but it actually forms a very fertile place for the purpose of irrigation. The place is made up of numerous layers of Loess.