Basically the left and the right halves of that map (and supergrid really) aren't connected by water (unless you go like 3/4 of the way south and then back up again). I made the road so I could easily explore the other half of the area. Now I can't fucking get anywhere without a huge detour.
EDIT: Although there's not much reason to head over there anymore anyway. That mountain was one of my main foraging grounds but now that's half gone too.