2000 Topps Stadium Club King of the Hill Game Used Mound Dirt
Topps actually made a whole set of these for the 2000 Stadium Club featuring both dirt from several pitchers mounds and batter boxes. I am not sure how authentic dirt can be, but if nothing else the card is a good discussion piece. I am not sure whether the dirt came off the mound during the 1999 or 2000 season, but they were both pretty spectacular years that that resulting in the Red Sox right hander winning the American League Cy Young Award.
Similar to the game used wall card of Piazza this card also features a relic from a common area on the baseball field. I am sure that the dirt probably is from the pitchers mound in Fenway Park, but who really can quantify the use of dirt on a pitchers mound. Needless to say, the concept of the game used dirt card did not make it past the 2000 Stadium Club set. However, I will say that I am going to find a copy of the McGwire batters box dirt card from this set.