What does the phrase "utterly McKinley" mean?

In a spoken introduction from a live recoding made in Pasadena, CA, in 1956, on the album Round About Midnight by Miles Davis, the MC Gene Norman is heard saying:

A little bit unlikely that so much fine jazz should happen in Pasadena
perhaps — I’ve heard Pasadena referred to as "utterly McKinley"

The audience laugh at this point, so it was evidently funny at the time/location.

I’ve tried researching the phrase, but can’t find anything reliable. I guess it might rely on some context that I don’t have.

You can hear it in context on Spotify.