The scrambler is a British motorcycle shaped by an American phenomenon. From the 1951 Catalina Grand Prix to the Pasadena Motorcycle Club's Greenhorn Enduro, four-stroke singles from AJS, Matchless and BSA ruled the California desert 50 years ago. Courses were mostly flat in those days, with plenty of long, straight high-speed stretches. But after hundreds of riders carved up the desert, it was tough to maneuver without crashing or getting stuck. Running out front required a balance of speed, handling and horsepower, and 500cc singles delivered just that.