2. The U.S. Open Was Also Played on Clay
The U.S. Open was played briefly on clay from 1975 to 1977, making it the only major tournament to have been played on three surfaces. Tennis icon Jimmy Connors won the U.S. Open on all three surfaces, while Chris Evert won on two — clay and hard court.
The clay material was technically called HarTru, an igneous crushed basalt stone from the Catoctin Mountains of Maryland. The gray-green color comes from epidote, a mineral that is in the stone. HarTru is a faster material than European red clay, and it is said that the change to clay was an attempt to make the tournament more television-friendly as it created more contrast between the surface and the ball and induced a slower game.