In general, the borders of the federal state of Washington are in accordance to natural physical features.
The border with Canada,, the northern one, is defined by the Okanogan Range and the Kettle Range, two highlands.
The border with Oregon, the southern one, is defined mostly with the Columbia River, and partially by the Blue Mountains.
The border with Idaho, the eastern one, is defined with the edge of the lowland part of the Columbia River Basin.
While the western border is a border with the open water of the Pacific Ocean.