Collectors, agents, and historians are taking close-up looks at the artifacts. One example is a letter written by the father of the missions, Junipero Serra, in 1776.
"It talks about establishing the missions in California, the mission road, and there's his signature, Junipero Serra," says Richard Frajola, a postal historian-dealer.
The only other know father Serra letter recently sold for $350,000.
There is also a letter sent on the Pony Express, two months after the service began.
A stock certificate for a mining company shows the buyer was Samuel Clemens, otherwise known by his pen name, Mark Twain.
They are items that chronicle the development of the west.
"Real letters that talked about real people that were handled by the postal system," says Frajola.
Frajola was the agent for Floyd Risvold who came west when he was 19 and became fascinated by western history. Risvold would spend 50 years collecting.
"He was very specific, he only wanted the best of something. He wanted one letter that could tell the story the best it could be told," says Frajola.
Risvold died in June and now the family is sharing his collection.
"It was part of our life and he would show is things when he bought them," says Diane Pearson.
His daughters, Pearson and Kathy Cathcart, have contracted with Spink Shreves Galleries to auction the collection in New York at the end of the month.
"We're so proud of what he's accomplished and being able to share that, and see that go on as he had hoped that collectors, young collectors today could continue collecting," says Diane.
So his legacy will continue. Just an idea of how important this collection is, the auction catalogue is in three leather bound books that weigh nine pounds.
And friends remember Floyd Risvold who always told people: "Keep your powder dry."
"It was his way of saying goodbye to people; keep your powder dry and your hopes high," says Cathcart.
The auction could bring in $5 million.