Dirt track racing is a form of motorsport held on clay or dirt surfaced oval race tracks often used for thoroughbred horse racing. Dirt track racing started in the United States before World War I and became widespread during the 1920s and 1930s using both automobiles and motorcycles. Two different types of race cars dominate — open wheel racers in the Northeast and West and stock cars in the Midwest and South. While open wheel race cars are purpose-built racing vehicles, stock cars (also known as fendered cars) can be either purpose-built race cars or street vehicles that have been modified to varying degrees.. There are hundreds of local and regional racetracks throughout the nation.