It looks like that yellow (3-day) spot is a bit of land with no assigned zipcode, per this site:
https://zipmap.net/Wyoming.htm
And there's this odd thing there (turn on satellite view):
https://www.google.com/maps/place/Wyoming/@42.6903821,-107.5...
Might be the remains of an airfield or something.
Perhaps it was an missle silo.
Re:USPS Service Standards Maps
by orangepurple on Sunday March 27, 2022 @11:41PM
(#30826913)
There appears to be a white disc at the end of the removed runway with unnatural dirt patterns. Maybe that's a launch silo? It almost seems like there used to be a runway there to bring in materials and build an underground structure (white disc). The structure does not appear to cast a shadow, potentially indicating that it is flush with the ground.
Why is there a tiny portion of the center of Wyoming that is 3 day service when the surrounding area for hundreds of miles has 4 day service?