The Palouse Prairie (palouseprairie.org)The region of southeastern Washington and adjacent Idaho that has rolling hills on deep soils is known as the Palouse. On its eastern border, this region is bounded by the forests of northern Idaho, and the Snake River forms its southern boundary. To the north and west, the Palouse is bounded by areas of flat terrain and shallow soils, places where the deep soils were scoured away by ice or water during past glaciations or floods. Some scientists use a more inclusive definition of the Palouse; they consider areas to the west and south and even parts of northwestern Montana to be part of the Palouse.