1. Post route map of the territories of Montana, Idaho, and Wyoming with parts of adjacent states and territories : showing post offices with intermediate distances between them and mail routes in operation on 1st October 1883 Yale Public content 1883. 2002-09-20T19:14:15Z. 2017-07-04T21:14:42Z. United States. Post Office Department. The Dept. English. Public. Montana, Idaho, and Wyoming.