By Ben Marks — On October 21, 1976, a small group of cyclists and a dog named Junior gathered on Carson Ridge, which rises just west of Fairfax, California. It was mid-morning and the sky was bright blue, a beautiful day for racing 50-pound vintage Schwinn Excelsior clunkers down Cascade Canyon Road, whose winding dirt surface plunges 1,300 feet in less than two miles, past serpentine outcrops, low-lying chaparral, and scattered oaks on its way to the confluence of San Anselmo and Cascade creeks. "No...