The Mexican province of Alta California granted cattle ranches to many prominent citizens. The properties were huge, so surveying was very expensive and often vague. These ranches dissipated into smaller holdings after the US takeover of the state. At the time, people often owned an "undivided" fraction of a ranch. For example, Martina Castro deeded undivided ninths of her Rancho Soquel to her nine children. Any co-owners who lived on the undivided ranch presumably did so under mutual agreement.
Today, we have a similar concept called tenancy in common, but land offered publicly for sale always seems to have fixed boundaries and no co-owner. The ownership of undivided fractions of rural land may have gone out of style.
How did surveyed lots replace undivided parts? Did a new law change the regulatory context, or was undivision just a quirk particular to the ranchos and the uncertainty around their legal confirmation?