We compare, on a global scale, the degree of correlation between orientation of stream networks and topographic aspect on Mars and Earth. The orientation of streams on Earth is a reflection of local, underlying geology but, in general, it correlates with regional topographic aspect. However, the orientation of valley networks, prominent features on Mars, thought to be fossils of ancient streams, are shown not to be correlated with topographic aspect. Instead, we show that orientations of valley networks are highly dispersed with only a very weak preference to the regional topographic aspect. We attribute this dispersion to significant altering of topography by impact cratering which is not matched by sufficiently efficient runoff erosion. Such explanation is supported by the fact that local regions on Mars with relatively low crater density display a level of correlation between valley orientation and aspect comparable to that calculated for terrestrial surfaces. In addition, the cratering explanation is further supported by means of landscape evolution simulations. Our finding provide an additional support to the idea that climate on early Mars, although wetter than its present climate and capable of producing rainfall, was nevertheless too arid to enforce (through erosion) correlation between stream orientations and topographic aspect.