Could very well represent the northern border. Looking specifically at the two indicated ports of entry, one potentially being Porthill, Idaho and the other potentially Whitetail, MT, each of these has an "international" airport at the border. Eckhart Airport in Porthill and Poplar Airport in Whitetail. Both are remote border crossings. And probably very porous.
Not anymore. Within the past month I came across the border from Canada into Montana.
Customs was very thorough; they spent time checking out information on their computers, and surprisingly, had a large staff on duty. No more waving you through like they used to do.