I'm not sure what you mean by "the great California Yorba fortune". The Yorbas were traditionally land rich, but money poor. The "fortune" if you want to call it that came primarily through the hide and tallow trade before the 1850-1860s, then some "wealth" through sheep raising. By the death of Bernardo Yorba, the family holdings began to break up. By the 1870s, most Yorbas were "working class", holding jobs like police constable, watchman, small holdings farmers, vaqueros, etc.