Niner "Demo Day" at Joaquin Miller Park, Oakland, CA - Sunday 10-3
Here's a pretty cool chance to ride a variety of 29'er MTBs from Niner on Sunday.
They'll have platform petals available for you to use (bring your sneakers), or if you have your own favorite mtb shoes/pedals, bring 'em. And of course everyone should bring a helmet.

My coworker at Wrench Science is putting on this totally free demo event: