Travelers between Corrine or Kelton, Utah, and Virginia City, Montana began asking the proprietors at the Anderson Brothers store at Taylor Bridge to hold their money for them, keeping it safe until they would return. Taylor Bridge was a toll bridge at what was first called Taylor Bridge, then Eagle Rock as it became a town, and Idaho Falls when it became a city. The Anderson Brothers store was one of the first to serve travelers going back and forth between the Montana mines and Utah supply points.
As the only spot for hundreds of square miles that had even a hint of security, Anderson Brothers began keeping goods and wealth as a favor to miners, often with no receipt except a handshake. The miners would drop back by in person when they were ready to claim their possessions, or they’d send a note by mail to the Anderson Brothers store requesting they send it on to another destination.
The Anderson Brothers began to worry about having money and gold sitting around on shelves beneath the counter, so they ordered a safe. That safe and its continued use inspired them to open Anderson Brothers Bank.
The store became an unofficial post office the same way it became an unofficial bank, by being a place where people stopped on their way to someplace else.
The post office came about because people would leave letters in a box, hoping someone going more or less in the direction the letter was headed would pick it up and take it a few miles closer. People just pawed through the mail looking for a letter for them or finding a letter for someone else that they could move on down the road a bit.
If that sounds like a haphazard way to run a post office, it sounded the same way to a postal inspector that happened through on his way to Montana. When he pointed this out to the Anderson Brothers, according to an article in the August 26, 1932, edition of the Post Register, one of them kicked the box of letters out the door and said, “There is your post office. Take it with you, and if you don’t like the way we do things around here we will throw you after the box.”
The inspector had a change of heart and decided they could continue their unauthorized post office, which they did until an official one was established a few years later when the railroad arrived.