Love of Home and Friends—like the ridge behind a Bunker! (Meaning)

I’m translating a fable by George Ade called "The Fable of the Visitor Who Got a Lot for Three Dollars." In the following extract, the phrenologist is telling his customer how he is based on the form of his head:

"Well, well!" said the Learned Phrenologist "Enough Benevolence here to do a family of Eight. Courage? I guess yes! Dewey’s got the same kind of a Lump right over the Left Ear. Love of Home and Friends—like the ridge behind a Bunker!"

My issue is with the phrase "Love of Home and Friends—like the ridge behind a Bunker!" I assume "like the ridge behind a Bunker" is a metaphor, but I feel like I can’t get the meaning. Would you please help me with this?