The landform known as Bethel Island was created between 1859 and 1870 by several men, see the names and survey numbers below. (Source: California State Archives for Land Patent Certificate of Purchase for Swamp and Overflow Surveys Numbers 80, 81, 82, 83, 225, 226, 227 and 250). Alonzo Stone purchased much of the property formerly owned by Warren and Anne Bethell, and the area was briefly referred to as the "Stone Tract" in the 1930s. Prior to this, it was referred to as "Sandmound Ranch", "Sandmound Tract" or "Bethel Tract" and contained an estimated area of 6,000 acres (24 km2), and did not become an island until 1911, when Dutch Slough was dredged eastward to join with Sandmound Slough. East Contra Costa Historical Society has been made aware of these inaccuracies, however has not yet updated their website.[8]

Though it was common for the era to name the post office after the postmaster, and for the communities to assume the name of the post office, there are some references to the area as "Bethell" referring to the Sand Mound Ranch farm established by a coalition led by Franklin's older brother, Warren King Bethell, Nicholas Harris (Sheriff of San Jose) and James C. Smith. Prior "owners" of these lands were considered "land speculators" and only performed the minimum amount of improvements to reclaim the land in order to secure land patents. This may not be a fair assessment of all, since some did make an honest attempt to reclaim the lands only to be forced out by changes in governmental policy and financial constraints.