Unfortunately, the damage the black ocean left behind was much worse than one bottomless pit. The black ocean didn't take out a city and call it a day. Instead, it took out a city and everything between that city and the next one.
Then it erased everything between the second city and the third one. That still wasn't enough for it and he took out several more cities after that, leaving a trail of emptiness in its wake.
If the depression the black ocean left behind was narrow, it would have been called a valley. But it was too wide to be called a valley.
The depression was so wide it contained a hundred cities standing side by side. It was also deep enough to contain the hundred cities sitting on top of each other.
The black ocean had practically shaved off the surface of the continent and left something akin to the ocean floor in its wake. So everyone decided to call the depressions the Great Black Ocean Trails.
