There are a number of east-side schools that have a fair number of corps members as well- Central Valley, Mt Spokane, and Mead (Spokane) and Hanford, Chiawana, and Kamiakin (Tri-Cities) all had decent representation at various corps this year as far as I know. Also, while there are comparatively few "very strong" marching programs on the east side of the state, CV and Mead both have had exceptional success in the region, and schools such as Mt Spokane, Hanford, and Chiawana have all shown marked improvement in the last few years- at least, from my perspective.