Dumpster diving may be trendier, but if you want blackberries, try foraging on Tank Hill. At the market, they're $2 per basket even at the height of the season, but at at this small park (which has a great view) the blackberries are fat, free, and everywhere. The unblocked sun bakes this place all day — perfect berry conditions — and if you leave the sidewalk and flank the patch or scramble around back to attack from the rear, you can shove your way in among the blackest, juiciest monsters in town. The bushes sag with guaranteed organic berries in July and August, and as you gaze upon the Berkeley Hills, the Bay, and Marin, you can leisurely pack away enough fruit for a pie in 30 minutes, enough for a quart of wine in an hour. Leave the red ones; they'll be ripe tomorrow.