There are a few reasons why Baja California is sometimes called Lower California. First, the peninsula is located to the south of the U.S. state of California. This means that it is lower in latitude than California. Second, the peninsula is lower in elevation than California. The Sierra Nevada mountains in California are much higher than the mountains in Baja California. Third, the peninsula is less developed than California. This means that it has a lower population and a less developed economy than California.
The term "Lower California" is sometimes used to distinguish the peninsula from the U.S. state of California. However, the term "Baja California" is more commonly used today.