Mars Once Had Oceans, New Evidence Suggests

A hypothesized shoreline was spotted during the late-1970's Viking-missions. Unfortunately, these shorelines rise and fall in vertical height (several kilometers in some spots) along their length. Thus it shouldn't make sense to say that they are shorelines because shorelines should form at sea level. To account for these elevation changes, researchers have found new information leading them to believe that Mars' poles, along with the planets' axis of spin, have been wandering, moving 1,850 km in the last 2 - 3 billion years. When the spin axis moves adversely to the planets' surface, deformation occurs and is "recorded in the shoreline." It is fair to infer that this happened on Mars because there is presumably clear evidence for such a phenomenon occurring on Earth.

http://news.nationalgeographic.com/news/2007/06/070613-mars-oceans.html