Railroads used to be the primary means of getting mail from one town to another, with an ability to get the mail to its destination with a speed not rivaled today. Any town along the railroad in the Big Bend region of the Columbia Basin owes its livelihood to mail service by rail.
An excellent description of the railway post office (RPO) can be found here:
As the public viewed railroad travel as old-fashioned and took to the automobile, railroads found it harder to maintain branch line service to every remote place. This made it harder to deliver the mails to those places. The United States Post Office canceled mail contracts with the railroads, and moved the mail to truck.
The list below shows the length of time RPOs operated in the Big Bend.
Mansfield & Wenatchee (endpoints of RPO)
Great Northern (railroad RPO operated on)
7-9-1911 to 1-18-1925 (start and end dates of RPO)
Oroville & Spokane
1907 to 4-1-1925
Note: This train did not operate via Wenatchee
Oroville & Wenatchee
7-10-1914 to 2-19-1954
Spokane & Seattle
11-1-1893 to 10-14-1934
Williston & Seattle
Great Northern/Burlington Northern
10-14-1934 to 4-30-1971
The below dates are all for the same track, with the end point changing to Adrian for a time, and then Coulee City changed its name to Coulee and back. The gap of 3 years in service is unexplained.
Spokane Falls & Almira (line not complete to Coulee City yet)
5-1-1890 to 6-30-1890
Spokane Falls & Coulee City
7-1-1890 to 1891
Spokane & Coulee City
1891 to 2-15-1904
Spokane & Adrian
2-15-1904 to 6-28-1925
Spokane & Coulee
6-28-1925 to 4-11-1937
Spokane and Coulee City
2-25-1940 to 1-31-1954