Almost all gas stations and drugstores sell maps both of the locale you’re traversing and of the whole state. California State Automobile Association (CSAA, www.csaa.com ) offices offer maps to members for free.
Many local and regional visitors centers also offer maps, but you’ll need to pay a few dollars for the bigger and better ones. But if all you need is a wine-tasting map in a known wine region, you can probably get one for free (plus a few tasting coupons) at the nearest regional visitors center. Basic national park maps come with your admission fee. State park maps can be free, or can cost a few dollars at the visitors centers.