re: Crack or crock?
Very intriguing interpretation!
If it's correct, we still face the question of age. This feature, however it formed, is still vastly newer than the rest of the canyon. Yet it should have taken a significant length of time to erode a falls so many kilometers, shouldn't it? And if there were flows for only "dozens" of years altogether, something isn't fitting too well.
It would help if we had more images of this feature as well as images of other, similar, features if there are any.
Meanwhile, I hope your interpretation proves the correct one!