Neil Young joined fellow Canadian rockers -- and 2011 Album of the Year Grammy winners -- Arcade Fire for a stunning version of the Crosby, Stills, Nash & Young classic 'Helpless' Saturday during the opening day of Young's annual Bridge School Concerts at the Shoreline Ampitheatre in Mountain View, Calif.

As is tradition, Young closed the opening night with a solo performance -- his set included 'Comes a Time,' 'Sugar Mountain,' 'Long May You Run' and 'Heart of Gold' -- but this year it was his guest performances that provided the highlights of day one. In addition to playing with Arcade Fire, Young surprised Beck for a run at the former's 1979 track, 'Pocahontas,' sat in with Mumford & Sons for a cover of his song 'Dance Dance Dance,' and joined Dave Matthews and Tim Reynolds onstage for a version of the traditional folk tune 'Oh! Susanna.'

Other performers Saturday included Eddie Vedder, Los Invisibles (featuring Carlos Santana), Devendra Banhart and Norah Jones. This year's Bridge School gigs mark the 25th anniversary of the annual festival. Young hosts the shows as a fundraiser for the school, which he started in 1986 with his wife Pegi for children with severe physical disabilities.

The previous Friday (Oct. 14), Young hosted the the Heart of Gold Gala at San Francisco's Regency Ballroom, another event in support of Bridge School. The evening featured a sit-down dinner and memorabilia auction, and ended with performances including a few songs from Neil and Pegi, a solo set from Dave Matthews, and then a Young and Matthews duet on 'Oh! Susanna' and Bob Dylan's 'Gotta Travel On.' The gala raised $1.5 million for the Bridge School.
Neil Young and Arcade Fire Perform 'Helpless' At the 2011 Bridge School Concert