The Gulf of California is also known as “the Sea of Cortez” – though, as with Castellano as alternative language name, the usage Mar de Cortez is far more common in Spanish than the English translation is in English. (My admittedly-casual knowledge of matters Mexican suggests that Mar de Cortez is preferred over Golfo de California in Spanish, though both are used.)
I was unable quickly to identify some other examples of Bajo and Baja used geographically, but I seem to recall districts in South American countries being named “Alto [Rivername]” and “Bajo [Rivername]” in much the same way as some French departements are Bas-Rhon and Haut-Rhon or similar examples.