Complex sentence: "The Peninsula," used on its own, refers locally to only the parts south of, and excluding, the city of San Francisco, roughly equivalent to the area served by the 650 area code, or sometimes to San Mateo County only.
Split into simpler sentences: The Peninsula, used on its own, refers locally to only the parts south of, and excluding, the city of San Francisco. It is roughly equivalent to the area served by the 650 area code, or sometimes to San Mateo County only.