Primus frontman Les Claypool and The Lumineers have signed on to perform at the annual Hardly Strictly Bluegrass Festival, a free weekend of concerts that'll be held October 5-7 at Golden Gate Park in San Francisco, CA. Other artists scheduled to appear at the event include Elvis Costello , Chris Robinson Brotherhood , and former Rilo Kiley frontwoman Jenny Lewis , plus more. 

The festival, which celebrates bluegrass and other genres of roots music, was founded by billionaire businessman F. Warren Hellman , who passed away last December at age 77 after a battle with leukemia. To see the full artist lineup for the musical extravaganza, visit StricklyBluegrass.com .

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