The ranch covered over 80 square miles ( 21,000 ha ) .
The ranch extended over 8 miles ( 13 km ) to the San Joaquin River , where Marsh 's Landing was built ( near present - day Antioch California ) .
The ranch covered over 80 square miles ( 21,000 ha ) , and extended over 8 miles ( 13 km ) to the San Joaquin River , where Marsh 's Landing was built ( near present - day Antioch California ) .