California grows about 80% of all fruits and vegetables in the U.S., so California seasons (such as they are) are, in some ways, national seasons. That is, you may not be able to get something locally, but even buying nationally keeps you in touch with the hemisphere's seasons, which is something. You can also look up produce by seasons (spring, summer, fall, winter) or region.

Apples, late summer through fall (cold storage until spring)

Apricots, late spring through early summer

Artichokes, spring and again early fall

Arugula, available year-round but best in spring and fall

Asparagus, spring

Avocados, classically summer, but now harvested year-round

Basil, summer

Beets, year-round

Belgian Endive, available year-round but best in fall and winter

Blackberries, summer

Blueberries, summer

Boysenberries, early summer

Broccoli, year-round but best in fall and winter

Broccoli raab, fall through spring

Brussels sprouts, late fall and winter

Cabbage, best in late fall and winter but available year-round

Cantaloupes, late summer

Cardoons, winter and early spring

Carrots, year-round

Cauliflower, best in fall and winter but available year-round

Celeriac/celery root, fall and winter

Celery, best in fall and winter but available year-round

Chard, summer and fall

Cherries, late spring and summer

Chickpeas (a.k.a. garbanzo beans), fresh in summer (dried year-round)

Chicories, fall and winter

Chiles, summer

Clementines, winter

Collard greens, year-round

Corn, summer

Cucumbers, summer

Edamame, fall

Eggplant, summer and early fall

Escarole, fall and winter

Fava beans, spring

Fennel, fall through spring

Fiddleheads, spring

Figs, summer and fall

Garlic, summer and fall (stored year-round)

Gooseberries, summer

Garlic scapes/green garlic, spring

Grapefruit, winter and spring

Grapes, late summer and early fall

Green almonds, spring

Green beans, summer and early fall

Green onions, spring through fall

Horseradish, fall and winter

Huckleberries, late summer and early fall

Jerusalem artichokes/sunchokes, fall and winter

Kale, best in fall and winter

Kiwis, winter and into spring

Kohlrabi, late fall through spring

Kumquats, late winter and spring

Leeks, fall through spring

Lemongrass, summer and fall

Lemons, winter and spring

Lettuce, available year-round nationally but best in spring

Limes, late summer and fall

Mandarins, winter

Mangoes, summer

Marionberries, summer

Melons, summer and early fall

Mint, year-round

Morels, spring

Mushrooms (cultivated), year-round

Mushrooms (wild), spring through fall

Nectarines, summer

Nettles, spring

New Potatoes, spring

Okra, late summer and early fall

Onions, spring through fall (stored in winter)

Oranges (Navel), winter and spring

Oranges (Valencia), spring and summer

Oregano, year-round

Parsley, year-round

Parsnips, fall through spring

Peaches, summer

Pears, fall

Pea greens, spring

Peas and pea pods, spring and early summer

Peppers (sweet), summer and early fall

Persimmons, fall and early winter

Plums & pluots, summer

Pomegranates, fall

Pommelos, winter

Potatoes, late summer through fall but available from storage year-round

Pumpkins, fall

Quinces, fall

Radicchio, late summer through early spring

Radishes, spring through fall

Radishes (daikon, watermelon, other large varieties), fall and winter

Rapini, fall through spring

Raspberries, summer

Rhubarb, spring and early summer

Rosemary, year-round

Rutabagas, fall and winter

Sage, year-round

Salsify, fall and winter

Scallions, spring through fall

Shallots, summer and fall (from storage through winter)

Shelling beans, summer and early fall

Snap peas/snow peas/pea pods, spring

Sorrel, year-round

Spinach, year-round

Spring Onions, spring

Squash (summer), summer

Squash (winter), fall and winter

Stinging Nettles, spring

Strawberries, spring and summer

Sunchokes/Jerusalem artichokes, fall and winter

Sweet Onions, spring and summer

Sweet potatoes, fall and winter

Tangerines, winter

Thyme, year-round

Tomatillos, late summer

Tomatoes, summer

Turnips, fall through spring

Watercress, year-round

Watermelons, summer

Winter Squash, fall and winter

Zucchini, summer

Zucchini Blossoms, summer