First fat-bike with a derailleur ridden off road1973
As far as I know it was Russ Mahon of Cupertino, California (75 miles south of Marin County), who came up with this combination, in 1973. He grafted derailleurs onto a 1930s balloon tire bike built by the Cleveland Welding Company. He also put thumbshifters on this bike. Three Cupertino riders including Mahon showed up at a Cyclo-cross race in Marin, December 1974, pollinating Marin with these ideas. They then departed the scene for more than 20 years.