Born in Bilbao of an old Basque family,[1] he was sent by the viceroy of New Spain, Antonio María Bucareli y Ursúa, to explore the area north of Alta California in response to information that there were colonial Russian settlements there.
The Spanish claim to Alaska and the Pacific Northwest had dated back to the 1493 papal bull (Inter caetera) and rights contained in the 1494 Treaty of Tordesillas.
These two formal acts formed the basis of Spain's claim of the exclusive right to colonize all of the Western Hemisphere (excluding present-day Brazil), including all of the west coast of North America.
A first expedition led by Juan José Pérez Hernández in 1774 with just one ship, the frigate Santiago (alias Nueva Galicia [2]), did not reach as far north as planned.
The 36-foot-long (11 m)[4] Sonora, with a crew of 16, was to perform coastal reconnaissance and mapping, and could make landfall in places the larger Santiago was unable to approach on its previous voyage.
By design, the vessels parted company on the evening of July 30, 1775, with the Santiago continuing north, to what is today the border between Washington and British Columbia, Canada.
There, and near a Russian settlement on present day Kodiak Island, the Spaniards performed numerous "acts of sovereignty" claiming the territory.