I am about 40 miles north of Sacramento in the valley. What zone am I?

Try this:

http://www.usna.usda.gov/Hardzone/ushzmap.html

Also useful is the Sunset Western Garden Book, which breaks down western zones into very small areas. For example, I'm US zone 10, and also Sunset zone 22. On the CA Forum at the Gardenweb site, people always identify themselves by both zones.