Schwinn first introduced the balloon tire (2.125" wide) to the US market in 1933 and most of the early converted mountain bikes were based on the pre-war Excelsior-type frames.  The first hand built bikes used the geometry from the early Schwinns as well.  Despite all this "history", Schwinn did not pick up on the mountain bike trend and many feel it was a major contributing factor to their bankruptcy.  If you check out the specification sheets below you will notice that the early Schwinn bikes were Varsity type "gas-pipe" frames with limited gearing, one-piece cranks, super high-rise handlebars and caliper brakes.  These were not specs that would excite a mountain biker and made the bikes best suited to town or beach riding.  Starting with 1985 I am just listing from the Sierra model and up.