If you’re a locavore (“one who tries to eat only locally grown foods”), you may find Epicurious’s Seasonal Ingredient Map useful. Pick any month, then click on your state, and it shows you a list of currently-available local produce:
Mouse over a produce item, and get links to produce definitions, pictures, recipes and cooking tips. Not perfect, especially for states with a wide variety of climate zones. For Arizona, it says the growing season is currently dormant, but there is fresh produce currently being grown in the warmer southwest corner of the state.