Mt. Washington is an eroded volcanic plug in the central Oregon Cascades, the main rock types are basalts, including andesite. As with most Oregon cascade mountains the rock quality is generally crumbly and poor, however the quality does improve at the summit's exposed volcanic plug (still not super though). The majority of summits seem to happen from mid-June through September, although year round summit possibilities exist. There are several routes to the summit though the most popular is the North Ridge route. Make sure to sign the summit register!