A Giant Racer Making a World's Record. The Bonneville Salt Flats is a salt deposit left by the receding of ancient Lake Bonneville. This deposit covers about 159 square miles extending some nine miles along U. S. Highways 40 and 50 and the Western Pacific Railroad. The salt is white, crystalline aggregate, porous, hard and rigid so that it supports loaded trucks. In 1912 this area was tested as a race track and has since proved to be the greatest automobile speedway in the world. in 1931 Ab Jenkins of salt Lake City broke all former world speed records. Here on September 15, 1938, John Cobb established a record of 350,07 miles per hour. the next day Captain G. E. T. Eyston set a world's record of 357.50 miles per hour. Aug. 26, 1939, John cobb again became the world's automobile speed king by driving his car 369.74 miles per hour.