Captain John Downes Wilson was born in Dundee, Scotland in 1798. By the time he was 30 he was master of the Thomas Nowlan, a ship trading in hides and tallow on the California coast. Wilson was captain of several ships, including the Ayacucho, a ship described in some detail by Richard Henry Dana in his book Two Years Before the Mast.
In 1835 Wilson married General Vallejo’s sister-in-law, Maria Ramona Carrillo de Pacheco, changing his name to Juan (or even Juan Huilsons), converting to Catholicism, and becoming a Mexican citizen.
In 1837 he received the 18,833 acre Rancho Los Guilicos (named for the nearby Wappo village known as Wilikos) through a formal land grant. He received grants to other ranchos in Alta California as well, and never lived at Los Guilicos. In 1852 Wilson filed a claim to the land with the U. S District Court to clear the title, although it had already been sold to William Hood and William Pettit.