Peter, I was able to find this link below that referred to a "James Sullivan, the well known horseman" and references another article with the date 1892 in it, so it might be the guy we're looking for, but since Google doesn't have the "cache" feature any more that highlighted search words and I don't have time to search the whole document (my lunch break is almost over), you are welcome to it.
Full text of "Breeder and sportsman"
http://www26.us.archive.org/stream/breedersportsma461905sanf/breedersportsma461905sanf_djvu.txt Awarded Gold Me da At California State Fair 1892. Every horse owner ...... Colusa county, this spring, in charge of James Sullivan, the well known horseman.