Cadillac Desert by Marc Reisner is the definitive account of water and agriculture in the American West — essential reading for understanding the landscape you're driving through, including the irrigation systems and water politics that made the Sacramento Valley into rice country.
The Mountains of California by John Muir is classic California nature writing. Muir spent much of his life in this state and his observations on the natural world remain vivid and relevant.
A Pacific Flyway waterfowl guide or California birding field guide is invaluable if you're visiting the Sacramento National Wildlife Refuge. The refuge hosts dozens of species and a good guide will help you identify the geese, ducks, and waders in the fields and wetlands.
A Sacramento Valley history or California agriculture book will put the surrounding flatlands in context — this region was transformed by water projects and rice cultivation in the 20th century, and the story of that transformation is surprisingly rich.