Eastern Washington is what us Western Washingtonians call the part of the state that lies east of the Cascade Mountains. Generally, it's much more like Idaho than it is like Western Washington. Very flat, full of farmers and country folk, and with very few towns of notice (the exception being Spokane).

The Grand Coulee Dam is over there, as well the DoE's Hanford Center. Most of the Indian Rezes are there, as well as a few Wildlife Refuges. Yet, strangely, most of the National Forests in Washington are situated here in the west.

There are some who think that Eastern Washington should secede to Idaho since they're so similar. However, if we were to do that Seattle and most westerners would be trapped a mere hour or two from Idaho, with only the Cascades to fend off their pending potato invasion.