1970s1980s  There were a number of groups of riders in different areas of the U.S.A. who can make legitimate claims to playing a part in the birth of the sport. Riders in Crested Butte, Colorado, and Cupertino, California, played with bikes and adjusted them to the rigors of off-road riding. Customized heavy cruiser bikes, old 1930s and '40s Schwinn bicycles retrofitted with better brakes and fat tires, were used for freewheeling down mountain tracks in Marin County, California, in the mid-to-late 1970s.
The earliest forefathers of contemporary mtb were based around frames from cruiser bicycles such as those made by Schwinn. http://BikeTeamOne.com was the frame of option due to its geometry. Riders utilized balloon-tired cruisers and customized them with equipments and motocross or BMX-style handlebars, creating "klunkers". The term would likewise be used as a verb given that the term "mountain cycling" was not yet in usage.
These were called "Repack Races" and activated the very first innovations in mountain bike technology as well as the preliminary interest of the public (on Mt. Tamalpais in Marin CA, there is still a trail titled "Repack"in recommendation to these early competitors). The sport originated in California on Marin County's Mount Tamalpais.
Joe Breeze is typically credited with presenting the very first purpose-built mtb in 1978. Tom Ritchey then went on to make frames for a business called Mountain, Bikes, a collaboration in between Gary Fisher, Charlie Kelly and Tom Ritchey. Tom Ritchey, a welder with abilities in frame structure, also constructed the initial bikes.
The first mountain bikes were essentially road bicycle frames (with heavier tubing and different geometry) with a larger frame and fork to allow for a larger tire. The handlebars were also different in that they were a directly, transverse-mounted handlebar, instead of the dropped, curved handlebars that are typically set up on road racing bicycles.
Other factors were Otis Man and Keith Bontrager. Tom Ritchey built the first frequently readily available mountain bike frame, which was accented by Gary Fisher and Charlie Kelly and sold by their business called Mountain, Bikes (later altered to Fisher Mountain Bikes, then purchased by Trek, still under the name Gary Fisher, presently sold as Trek's "Gary Fisher Collection").