California Partition Law Blog
Yes. California law allows a co-owner to take out a mortgage without the other co-owners consent or knowledge.
Co-owning property with other parties can be quite a responsibility that can be difficult to manage. One particularly stressful aspect of managing property is managing the debt that comes with financing the property. Some parties may even want to take out more debt without letting their fellow co-owners know. If such a debt or encumbrance on the property is taken, it is still enforceable and allowable and can result in the sale of the entire property.