Earp had a long-standing interest in boxing and horse racing, and he refereed boxing matches in San Diego, Tijuana, and San Bernardino. In the 1887" San Diego City Directory", he was listed as a capitalist or gambler. He won a race horse named Otto Rex in a card game and began investing in race horses, and he also judged prize fights on both sides of the border; he was one of the judges at the county fair horse races held in Escondido, California, in 1889. The boom came to an end as rapidly as it had started, and the population of San Diego fell from a high of 40,000 in 1885 when Earp arrived to only 16,000 in 1890.