We discussed on this forum the fact the OMEGA instrument on Mars Express has found most sulfate deposits to be in geologically old regions on Mars. However, notably there have be found some sulfate deposits that appear to be geologically young in the north polar region of Mars. In fact, considering the youth of the surfaces in the north polar region in general and of the dunes these sulfates have been found on, the age of these deposits could be in the range of only thousands of years old.
This would likely require liquid water and volcanic activity in this region to form the deposits in this time frame, and indeed volcanic landforms have been found in the north polar region that appear geologically young.
Below is a post I made to uplink.space.com on the topic.

Bob Clark

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Proposal for landing site of the Phoenix Mars Lander.
posted at 7/16/2007 3:04 PM EDT
exoscientist

The Phoenix Mars Lander is scheduled to lift off for Mars next month:

Phoenix Lander Prepared for Martian Dust Storms
Wednesday, July 11, 2007
http://www.foxnews.com/story/0,2933,288831,00.html

It is to land in the north polar region of Mars but the exact lander location has not yet been chosen.

I propose as possible lander sites those areas that have been suggested to contain geologically young polar volcanoes:

TOPOGRAPHY OF SMALL VOLCANOES AT THE MARGIN OF THE MARS NORTH POLAR CAP.
S.E.H. Sakimoto1, J. B. Garvin2, M. Wong1, and H. Wright1,3; 1(USRA at NASAÕs GSFC, Code 921, Greenbelt, MD 20771 USA; ****@denali.gsfc.nasa.gov), 2(NASA's GSFC, Code 921, Greenbelt, MD 20771 USA; ****@denali.gsfc.nasa.gov), 3 (USGS, Menlo Park, CA, 94025).
http://www.lpi.usra.edu/meetings/polar2000/pdf/4092.pdf

Also, dunes in the north polar region have been the only sites so far that are geologically young proven to contain sulfates:

CRISM SPECTRAL SIGNATURES OF THE NORTH POLAR GYPSUM DUNES.
L.H. Roach1, J.F. Mustard1, S. Murchie2, Y. Langevin3, J.-P. Bibring3, J. Bishop4, N. Bridges6, A. Brown4, S. Byrne7, B.L. Ehlmann1, K. Herkenhoff7, P.C. McGuire5, R.E. Milliken6, S. Pelkey1, F. Poulet3, F.P. Seelos2, K. Seelos2, and the CRISM team.
1Dept. of Geological Sciences, Box 1846, Brown University, Providence, RI 02912 ****@brown.edu, 2JHU/APL, Laurel, MD 20723, 3Institute d’Astrophysique Spatial (IAS), Orsay, France, 4SETI Institute, Mountain View, CA 94043, 5Washington University in St. Louis, St. Louis, MO 63130, 6JPL/Caltech, Pasadena, CA 91109, 7USGS, Flagstaff, AZ 86001
Lunar and Planetary Science XXXVIII (2007)
http://www.lpi.usra.edu/meetings/lpsc2
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