Why do you think the western peninsula is called Baja California Peninsula?

The western peninsula of Mexico is not called Baja California Peninsula, it is called the Baja California Peninsula. The name "Baja California" is derived from the Spanish words "baja" (lower) and "California", which was the name given to the entire peninsula by Spanish explorer Hernán Cortés in 1535. The peninsula was originally thought to be an island, and Cortés named it after a mythical island near the coast of Spain. The peninsula was later found to be connected to the mainland, but the name Baja California stuck.