Raft Guide Knock Knock Joke

To understand this joke, you need to know that two of the Rock Layers of the Grand Canyon are called Supai and Tapeats.

"Knock knock"

"Who's there?"

"Supai"

"Supai who?"

"Supai the beer and I'll buy Tapeats-a"

That last bit is suppossed to sound like:
You buy the beer and I'll buy the Pizza (for those of you struggling with the joke).