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/lpsc2007/pdf/1970.pdf

FORMATION OF THE MARTIAN NORTH POLAR GYPSUM DEPOSIT DURING THE AMAZONIAN.
K. E. Fishbaugh1, F. Poulet2, Y. Langevin2, V. Chevrier3, and J-P. Bibring2. 1International Space Science Institute (ISSI), Hallerstrasse 6, Bern CH-3012 Switzerland, ****@issi.unibe.ch. 2Institut d'Astrophysique Spatiale (IAS), Bâtiment 121, 91405 Orsay Campus, France. 3CEREGE, Europóle de l’Arbois, BP80, 13545 Aix-en-Provence Cedex 04, France.
Fourth Mars Polar Science Conference (2006)
http://www.lpi.usra.edu/meetings/polar2006/pdf/8041.pdf

The origin of the sulfate deposits is not known. It has been proposed extensive volcanism from far away volcanoes such as in Tharsis deposited sulfurous dust to the region and obliquity changes allowed the liquid water required for the sulfate formation.
However, it may be the near polar volcanoes are the source of the sulfate dunes. This would be very interesting because these volcanoes date to within only a few million years and some may still be active. Such volcanoes would have provided a local source for the large amount of sulfur required and the liquid water due to the heating generated.
Evidence this may indeed be the case is that some of the largest such volcanoes are close to the largest sulfate dunes. Compare the location of the sulfate dunes to the location of the volcanoes given in Fig.2 here:

MORPHOLOGY OF SOME SMALL MARS NORTH-POLAR VOLCANIC EDIFICES FROM VIKING IMAGES AND MOLA TOPOGRAPHY.
H. M. Wright1, S. E. H. Sakimoto2, and J. B. Garvin3, 1 ECO at
USGS, 345 Middlefield Rd., MS 977, Menlo Park, CA 94025 (****@core2.gsfc.nasa.gov), 2USRA at NASA's
GSFC, Code 921, Greenbelt, MD 20771, 3NASA's GSFC, Code 921, Greenbelt, MD 20771.
Lunar and Planetary Science XXXI.
http://www.lpi.usra.edu/meetings/lpsc2000/pdf/1894.pdf

and in Fig. 1 here:

NEAR-POLAR CRATERED CONES ON MARS: MOLA MEASUREMENTS AND IMPLICATIONS FOR VOLCANIC ORIGINS.
J. B. Garvin1 and S. E. H. Sakimoto2, 1NASA's Goddard Space Flight Center, Geodynamics Branch, Code 921, Greenbelt, MD 20771, garvin@denali.gsfc.nasa.gov, 2USRA at NASA's Goddard Space
Flight Center, Geodynamics Branch, Code 921, Greenbelt, MD 20771, ****@denali.gsfc.nasa.gov.
http://www.lpi.usra.edu/meetings/LPSC99/pdf/1492.pdf

However, the polar sulfate dunes that have been detected are seen around 80 N latitude which is too high in latitude for Phoenix which has to land at 70 N or lower. However, some of the north polar volcanoes do lie around 70 N latitude:

SMALL MARTIAN NORTH POLAR VOLCANOES: TOPOGRAPHIC IMPLICATIONS FOR ERUPTION STYLES.
S. E. H. Sakimoto1, J. B. Garvin2, B. A. Bradley3, M. Wong4, J. J. Frawley5, 1UMBC at NASA's GSFC, Geodynamics Branch, Code 921, Greenbelt, MD 20771; ****@core2.gsfc.nasa.gov, 2NASA HQ, Office of
Space Science, Code SR, Washington DC 20546-0001; ****@core2.gsfc.nasa.gov. 3Caelum at NASA's GSFC,
Geodynamics Branch, Code 921, Greenbelt, MD 20771; ****@core2.gsfc.nasa.gov, 4Department of Geological Sciences,
University of California, Santa Barbara, CA, 93106; ****@geol.ucsb.edu. 5Herring Bay Geophysics, Raytheon-
STX, at NASA's GSFC, Code 921, Greenbelt, Maryland 20771; ****@avalon.gsfc.nasa.gov
http://www.lpi.usra.edu/meetings/lpsc2001/pdf/1808.pdf

And, a map by CRISM of north polar sulfates shows they do occur at around 70 N though in lower concentrations:

REMOTE SENSING OBSERVATIONS AND IMPLICATIONS OF MARTIAN NORTH POLAR SULFATE DEPOSITS.
B. H. N. Horgan1, J. F. Bell III1, E. Z. Noe Dobrea2, and P. C. Thomas1, 1Cornell University, Department of Astronomy (****@astro.cornell.edu), 2Malin Space Science Systems (now at Jet Propulsion Laboratory).
Seventh International Conference on Mars.
http://www.lpi.usra.edu/meetings/7thmars2007/pdf/3241.pdf

It would be interesting to find out if the lower concentration sulfates at the lower polar latitudes also correlate in position to the lower latitude polar volcanoes.

Bob Clark