Actually, this would mark where the Dominion Lands Survey of the prairie provinces (Manitoba, Saskatchewan and Alberta) began. There's a PDF explaining the basis of the survey of Western Canada at: http://engrwww.usask.ca/classes/CE/316/Chpt-11-2006c(DLS).pdf#search=""principle%20meridian"%20DLS"

The monument was erected in 1930 and bears the following inscription:

""The first Monument on the Dominion Land Survey was placed July 10th, 1871, on the Principal Meridian, about half a mile South of this site.

The system, then inaugurated by Lieutenant-Colonel J. S. Dennis, Surveyor General, extends across the Prairies and to the Pacific Coast. It now embraces more than two hundred million acres of surveyed lands in Manitoba, Saskatchewan, Alberta and parts of British Columbia.

This site donated by the Honorable Aime' Benard and John T. Haig, K.C."
-from: http://www.mhs.mb.ca/docs/transactions/3/surveys.shtml

Although the practice may be dry, there's also a lot of history that went along with the actual measuring. Here's another PDF regarding the DLS and the Riel Rebllion (pages 2 & 3): http://www.sagt.sk.ca/ipfall05.pdf#search=""riel%20rebellion"%20DLS"

By the way, you might notice that some of the land immediately around the monument is not square, as the DLS PDF shows. This area is an example of a river lot survey. Immediately to the south is the Assiniboine River. The lots were surveyed so that they'd have access to the river. River lots are also explained in the DLS PDF.