At the hundredth meridian. That is literally where I am, according to Google Maps (I opened Google Maps to my current location, touched and held the screen until a red arrow blob appeared and the location showed my latitude and longitude. And indeed, the Great Plains begin at this location in Manitoba.
And there are buffalo – actually bison. Apparently what we call buffalo in North America (well, in the US – I have always called them bison) is actually only distantly related to buffalo. So these guys are Plains bison (in scientific parlance they are technical Bison bison bison, so really, really bison)