We recently went on a geology-heavy trip around Oregon, and this book proved to be a fantastic reference for the most part. The main downsides were that it was a little hard to pinpoint specific areas, as it covered fixed routes, and there were some that weren't addressed. It also was quite dated--there were passages in there that referred to Mount St. Helens without making note of the cataclysmic 1980 eruption! Still, I'd recommend the Roadside Geology series to anyone making similar trips. ( )