Region 3: The Northern Rocky Mountains

Extreme northeastern Washington has a history that is quite different from that of the other regions to the south and west. Although the rocks here contain both metamorphic and sedimentary structures, they share a similar degree of hardness. This means the region has been resistant to erosion, and, even though they are very old, these rocks remain exposed. Since this region was covered with ice during the last ice age, the mountains have been rounded by glaciation (Figure 4.9). Deep valleys were carved by glaciers flowing from the ice sheet.

Figure 4.9: Rounded topography of the Okanogan Highlands, Washington. This type of topography occurs on all scales, from these hill-sized outcrops to the region’s mountains.