I think that any map of a terraformed Mars is pretty much doomed to have some serious river violations. That said though, 60 years to full terraforming and population? If you are going to use a timescale that small, then I'd actually delete all of your "natural" rivers and replace them with existing formations or man-made canals etc. 60 years (and much of that would have had to be taken up with terraforming the place) doesn't seem to me to be enough time for riverbeds of the type we're familiar with to get carved out.

Guess I've pretty much outed myself as a "hard" sci-fi lover hehe. If you're going for something softer, you can probably disregard all that and chalk it up to the Force or some such