Here's one report that suggested Memnonia as a landing site for MSL because of geologically recent landforms suggesting liquid water flow:

NORTHERN MEMNONIA AREA: A POTENTIAL SITE FOR “MODERN” GROUND WATER.
Ronald Greeley and Ruslan Kuzmin
http://web99.arc.nasa.gov/~vgulick/MSLS99_Wkshp/Greeley_Kuzmin_Memnonia_abs.pdf

This report also gives Memnonia as one of the prospects for a future landing site:

Possible Martian Landing Sites to be Considered for Future European Exploration Missions.
P. Martin and M. Castillo, ESA - European Space and Astronomy Centre, PO Box 78, E-28691 Villanueva de la Cañada (Madrid),Spain; ****@sciops.esa.int.
http://www.lpi.usra.edu/meetings/lpsc2008/pdf/1794.pdf

Memnonia is also an area of high water content as indicated by GRS, which is also consistent with the frequent low lying clouds/fogs over the area:

WATER CONTENT IN THE ARABIA SOIL.
I. G. Mitrofanov , W. Boynton , M. Litvak , A. Kozyrev , A. Sanin and R. S. Saunders
http://www.lpi.usra.edu/meetings/lpsc2006/pdf/1643.pdf

Bob Clark