Pet Rocks were a 1970s fad conceived in Los Gatos, California by an
advertising executive, Gary Dahl. The first Pet Rocks were ordinary gray pebbles bought at a builder's supply store and marketed as if they were live pets. The fad lasted only about six months, ending with the Christmas season in December 1975; but in its short run, the Pet Rock
made Dahl a millionaire.
http://en.wikipedia.org/wiki/Pet_rock