There are several articles in California newspapers regarding Ammon Grigg being an apprentice horse jockey, 1937-1938. One says that he was born at Kuma. He became friends with another apprentice jockey, Freddie Gribble, from San Mateo.
They went to work for an old trainer, W. A. Thomas, who had made a champion of a racehorse named Lady Bowman, a mare that cost him $125 and won $50,000.
Because the trainer thought they had so much potential, he put them on his two best horses in the Celebration handicap(this is in the SF Examiner, 7/9/1937). Gribble was on Lady Bowman, Grigg was on a horse named Tarpwood.
Grigg also raced in Tiajuana as an apprentice jockey and won several races.
Tarpwood had run away while his groom was leading him to the infield, was still "fractious", and started late from the gate. In an amazing race, against experienced riders and horses, Grigg on Tarpwood came in 1st and Gribble was a close second.