>> One thing I noticed about Spanish-named cities: articles on them are quite rare in Spain, but fairly common in the United States: Los Angeles, Las Vegas, El Paso, Las Cruces, Los Gatos, El Centro, Los Alamos, …
I would not say they are rare in Spain but if we accept, for the sake of argument, that, in proportion, they are more common in the US than in Spain I would venture several possible reasons:
- They are new names compared to names in Spain which can go back to Roman times and have undergone successive transformations while Mexican names are newer and would tend to be descriptive (if not of native origin).
- Some of them are not even of Spanish origin. Many Spanish sounding names in California are quite new and just chosen for flavor. They may sound Spanish but some of them are not even correct Spanish. The article just gives the desired flavor.
Of those you mention:
Los Angeles I believe is short for Nuestra Señora de los Angeles (Our Lady of the Angels).
Las Vegas is descriptive: the lowlands
El Paso: The Pass