Au contraire. What defies common sense is the notion that a skinny little river, jumped in, around, and through the Canyon to reveal the layers. One would be better off saying that ancient Indians got their shovels and started digging...
How about this: Over thousands of years, the river dug a trench that eventually became a mile deep. How does that defy logic or common sense?
How does a global flood decide to carve out a massive canyon in one particular spot underneath the floodwaters?