At some point, he emigrated to Tepic, Mexico, where he made his living as a merchant.
One of the remarkable aspects of the book is that Forbes wrote it without ever having visited California at the time.
Forbes advocated that the United Kingdom take control of California, and suggested that the territory might be ceded to the UK in return for forgiving Mexico's debt to the British government.
However, another man, José de los Reyes Berreyesa, also lay claim to the mine on the basis that it lay on land given to him in a land grant by the Mexican governor of Alta California.
A complex legal case involving Mexican laws and the Treaty of Guadalupe Hidalgo described by The New York Times as "one of the most remarkable civil trials in this or any other country",[6] United States v. Andres Castillero eventually reached the United States Supreme Court whereupon it was finally decided in 1862 that, the mine was on the Larias grant, and that the furnaces and improvements of the company below the hill were on the Berreyessa grant.