Catalyst Rd off AZ-277, going a little over a mile to the Nova Biopower plant is shown as AZ 277 Spur in OpenStreetMap. I just drove it today, and it is indeed signed by ADOT as AZ 277S. There's a sign at the beginning, and an END sign at the gate, as well as directional signs on 277. It must be recent because Street View and StreetSide don't show it.
