NASA's Curiosity rover has found conclusive evidence that Mars once had large amounts of flowing water. A streambed and alluvial fan, similar to those found in the southwestern United States has been discovered.
Curiosity has high resolution images of coarse gravel that was deposited by flowing water on an alluvial fan. Note the sharp angular edges of the gravel which indicate that it was likely deposited by a flash flood like we see in the arid southwestern United States. Windblown deposits would not contain a mix of gravel, fine sediment and the whitish binding material that appears to be calcium carbonate cement, formed by the evaporation of water, like caliche on earth. Wind would likely have blown away the fines and rounded the edges of the gravel.
Earth's magnetic field and larger mass have helped earth retain water. Mars lacks a magnetic field so charged particles in the upper atmosphere can be lost to the solar wind.