For anyone near the San Francisco Peninsula, Webb Ranch opens their U-Pick berry patch during the summer. It's on Alpine Road just west of 280:

http://www.webbranchinc.com/farmers_upick_straw.htm

The page doesn't indicate when they will open for the season, but it tends to be early June.

A few years ago we went on the last day of the season and got some wonderful late season Navajo Blackberries.