Western Washington is full of Glacial till, full of Basalt and Granite. As one who spent a good amount of my childhood working in the "Rock Pile", which is what we called our yard, I can say firsthand digging in that soil is costly. When our neighbor put a pool in his backyard, we were offered $45 for every tiger tooth we could find that was broken off the bucket of the excavator they were using. When they dug out the foundation for our home, they left a row of granite boulders along one property line, which we covered with fill soil and planted shrubs in.