We're lucky in the Bay Area to have a number of micro-climates, which provide habitats for numerous species of birds. In addition, we have the bay itself, and the shorebirds and migrant species it provides. You could bird a new area every weekend, and likely not repeat a location form months.
We also have excellent birding sites within short drives. One hundred miles of coastline can hold numerous and distinct populations of birds. Then there is the Central Valley, and the Winter homes for hundreds of thousands of Ducks, Snow Geese, Sandhill Cranes, and Ibis. The Sierras provide their own unique environment, from the pine forests to high deserts.