It could be a few places. My guess is (only because I've done a similar job in that area) is NM, TX, OK and the 4th is either KS or CO.
Bear in mind. The 4 hours is only for the deliveries. Including unloading, delivery time itself. Which was pretty quick. About 20 minutes each. I drove for three times that, in the third state. That was going from pickup terminal to the first delivery. Then last delivery, back to terminal. Do think the north east is interesting. Possible. But not what I did.