Why is Summit's name ironic?

It is ironic because it is completely contrary to the
actual facts.  Summit, of course, means the top of something like a hill or mountain. 
But the narrator tells us that the town is down there, flat as a
flannelcake.

The reason for this, I think, is that the
narrator is trying to set up the idea that he and his partner are smart and the people
around the town are stupid.  The two of them think that they are going to come in and
easily get rich off the hicks in the town.   Having the town have this silly name helps
give this feeling that the narrator is superior to them.  That won't
last...