While not generally thought of as a destination area for rock climbing, the pure number of visitors that head to the bay area for other purposes make this a great location for a quick day on the rock in between other commitments.
You can climb year round in the Bay Area, provided that winter rains haven't pummeled the area too recently. Often, inland areas are extremely hot in the summer, though the coastal areas will stay pleasant.
American Big Wall climbing took its first roots here, with locals practicing their skills on local rocks before heading to Yosemite for its renowned cliffs. Almost every area that has a chimney in Northern California was first climbed by Warren Harding or Forrest Shute, and you will often see a piton stuck in the rock left over from climbers of another age.
Berkeley, Castle Rock and Sonoma will hold your attention for a great day of bouldering. Mount Saint Helena or Lover's Leap (in the Tahoe Area, but still only about 2 hours drive from most locations), or Table Mountain for a sport or trad experience.
Visitors and locals alike should check out the area along the Sonoma coast for a sport or bouldering experience unique to California, where waves, wind and rock found only here make an unforgettable day's climbing.
People with several days free in the Bay Area will probably want to head East to the Tahoe area in the Summer or Fall, to Yosemite for the trad folks, and perhaps all the way out (6-8 hours) to the Eastern Sierra areas like Bishop and Mammoth for a world class alpine, sport, or bouldering experience.
Unfortunately, a significant portion of the best climbing in the Bay Area is on private property, and unless you're in the know, you don't get to go.
This route begins below a large rock in the middle of the lower tier of climbing. A fun route that has an overhung section, some neato caves, and also a tough slab section at the top. Falling prior to the first clip is really not a great idea, as the bounce into the glassy sand deck wouldn't be fun. The section after the 2nd bolt is runout, but simple and fun. The crux is getting to the last bolt on a balancy slab. ...[more]
The Mezzones was a very cool bouldering area in the South Bay. It was pretty trashy, with graffiti on the boulders, but the sandstone was wonderful! It is now a golf course and therefore closed.