The map of time zones is more social than mathematical. As I look at this map, I realize that I gained Mike Jandreau, Tribal Chairman of the Lower Brule, as a friend. I showed up an hour early (to be fair, it was my third day at South Dakota State University) because I was on Central Time. I guess I should also credit Joel Clairmont with that new friend – Mike’s first question was “What do you know about tribal sovereignty?” and I replied with the information Joel had shared over our many trips carpooling to Montana State University. At any rate, Mike liked having someone who had a bit more up-to-date view of tribal sovereignty than Phil Sheridan’s.
Since there are 360 degrees in a circle, and 24 hours in a day, it makes sense that each time zone should measure 15 degrees of longitude. A glance at the map shows that Central time is 6 hours behind Greenwich, so it should start somewhere around 90 degrees west – Chicago is about 88 degrees, so close enough. Sidney (MT) is between 104 and 105 – so Montana’s eastern border is just about where mathematics would suggest it should be – but the eastern state line is not along a standard degree of longitude, but rather follows the 27th meridian west from Washington, DC.
“I am unsure just why the 27th meridian was chosen as the boundary between the two Dakotas and Montana and Wyoming. It may have been a number chosen “out of the blue” at the time Idaho Territory was established. The line does not coincide with any particular section or half-section line, or anything else of local or regional significance.
As I noted, the boundary line was not intended to follow the 104th degree of west longitude, but rather it was placed on the 27th meridian west of Washington. The boundary between North Dakota and Montana is supposed to be at 104°03’02.3″ (27° + 77°03’02.3″), and it is supposed to be a straight north-south line. However, a study of 7.5 minute topographic maps shows that the North Dakota – Montana boundary is at 104°02’46” at the South Dakota state line and at 104°02’54” at the International Boundary. That is, on the north end the boundary is approximately 533 feet farther west than it is on the south end.”
https://www.dmr.nd.gov/ndgs/ndnotes/Boundaries/Boundaries.asp
Mathematics doesn’t do much to determine the spot where Pacific time begins. I’ve heard stories that Montana’s western border was because of a surveyor error – that it was supposed to be along the continental divide. The actual story is equally interesting.
“Montana owes its contours to Sidney Edgerton, the state’s first territorial governor. Montana was split from the massive Idaho Territory that included what is now Idaho, Montana, and part of Wyoming. Lincoln chose Edgerton as chief justice of the Idaho Territory Supreme Court, and Edgerton was picked to make Montana’s case to become its own territory. Edgerton proposed making Montana’s western boundary along the Bitterroot Mountains, and as a result Montana gained the riches of the Bitterroot Valley as well as the eventual wealth of Butte.”
https://www.usatoday.com/story/money/2021/04/10/this-is-how-each-state-got-its-shape/43513185/
As for longitude 120 – where mathematics suggests we might locate the eastern line of the Pacific time zone? It’s closest to the western edge of Malheur County in Oregon – the one county in Oregon that is on Mountain time. Time zones have a fairly loose relationship with longitude.
Trego's Mountain Ear 