It was suggested to me in a comment here on HN, though I cannot now seem to find it by searching.
It paints a picture of how rich plant and animal life was before contact with Europeans. It shows how Native Californians depended on and deeply understood every root, leaf, flower, and fruit of every plant in their area. It explains how Native Californians were responsible for preserving and enriching the wildlife around them -- doing controlled burns, pruning, managing animal populations, sowing seeds, etc. These areas weren't "wild" or "pristine" at all, they were carefully managed and densely populated by Native Americans for over 10,000 years.
I think oftentimes we feel hopeless about our relationship to nature. We think if we touch it, we'll destroy it. Learning about how Native Californians lived shows how that's not inevitable at all.
I can to this thread to talk up the book too!