Specific to the Pacific Northwest:
The Northwest Nature Guide: Where to go and what to see month by month in Oregon, Washington, and British Columbia by James Luther Davis
The People of Cascadia: Pacific Northwest Native American History by Heidi Bohan – There are many, many pictures that makes looking at this with my nearly 4-year-old very fun and informative for him too.
Books on place generally:
The Idea of Wilderness by Max Oelschlagger
The Spell of the Sensuous by David Abram – This book profoundly changed the way I viewed going outside and ‘being in nature.’
Wild Pacific North West – Great website by an Oregonian about flora and fauna in the PNW.