An oasis on mars -- no palm trees but...
Most of the data returned from the Viking Landers and Orbiters confirm a highly desiccated surface for Mars. Life-as-we-know-it would seem to be impossible in such an ultra-dry environment. The Solis Lacus region is an exception. On occasion, Orbiter photos of this region have revealed heavy frosts and fogs. Further, the clouds here have more moisture in them than elsewhere on Mars. Conclusion: Considerably more water exists near the surface of the Solis Lacus region than elsewhere.
Since this area was the source of the great 1971 Martian dust storm, one wonders whether the unusual concentration of water has been revealed only because winds have stripped off the normally dry surface layer.
(Huguenin, R.L., et al; "Mars: An Oasis in Solis Lacus," Eos, 60:306, 1979.)
Comment. Close-up photos of Mars show many signs of fluid erosion. Abundant water may still remain well below the planet's surface.
Reference. Probable wet areas on Mars are cataloged at AME16 in The Moon and the Planets. Ordering information for this book is located here.