Portland is right on the Columbia River delta that the Eastern Washington flood basalt flowed through to get to the ocean. If you go closer to to Mt Hood there should be some outcroppings here and there along the road. But if you want to see large batholiths then NE Oregon in the Elkhorn mountains or SW Oregon near Medford and Granite pass.

Again the reason we don't see as many large granite formations are because of the trees and soil covering them up. So you have to find where it as been eroded away or where there has been massive uplift.

Well all of the Cascades are silica/granite. You just have to find places where the soil has eroded away or where roads have been blasted through the mountains. It's harder to find open granite formations in western Washington because of all the trees. There is Granite Mountain off of I-90 or going up past Paradise on Mt Rainier is always a good bet.

It may be ok because Friday is Veterans day so no school and many off of work hopefully not as bad of traffic. The worst traffic is through Tacoma and near JBLM.

My years of taking NW Geology courses are finally gonna pay off!!!!

So Washington is geologically speaking actually many different "islands" pushed together. The coastline when dinosaurs walked the earth was actually in Montana. Over time as the pacific plate was subducted under the N American plate it also brought along Islands. Those Islands couldn't be subducted and instead become part of the N American plate. The subduction zone moved west and repeated this until you get the coastline we have now. Now, the flood basalt happened by huge fissures opening up on the East side of the Cascades about 17 million years ago. Now, by then the Cascades were formed so the basalt couldn't reach Western Washington except through the Columbia River Valley. So to answer your question most of Western Washington is silica based while eastern Washington is basalt, except in the Columbia River Valley and one other weird little outlier.

This outlier is a series of tunnels near Mt St Helen's where there was a period of basaltic flow about 2000 years ago. This 300 year period is the only time Mt St Helen's or any Cascade volcano history thay flowed basalt as opposed to the thicker more explosive silica. Geologists have absolutely no idea why or how this happened. You can visit the tubes know as the Ape Caves now. I highly recommend it as a spring/summer activity as the road up to it is closed in the winter.

Sorry for the Geology lesson.... I have had this information stored in my brain vault and saw my chance to finally use it. Hahaha