Yep, that's right, it's really UPS Freight. I sure did a double take.
It turns out that these UPS trucks are subcontracted to take loads of pipes from California to Utah. But in order to make the trip worthwhile, they need to haul something back to California (that's called a backhaul). Someone figured out that hay would be a good load.
This friendly driver said they started backhauling hay about a year ago. She seemed to really like her job.