Q: Where are the Great Plains located?

Q: Where are the Great Plains located?
A: At the great airports!

This is a pun - the word plains sounds like planes, and the great plains are a large region in the middle of the united states, however the answer is not where those are located, but instead where the "great planes" are located, which is apparently the great airports.

There is a bit of absurdist logic to this - mediocre planes would be located in mediocre airports, and absolutely awful planes would be located is the worst type of airports.

Despite this joke being pretty bad, I sort of like it.