re: Proposal for landing site of the Phoenix Mars lander.
On Uplink.space.com was mentioned a possible landing site imaged by Hirise:
HiRISE | Possible Phoenix Lander Landing Site (PSP_002104_2485)
http://hirise.lpl.arizona.edu/PSP_002104_2485
It's located at 68.3°N lat., 233.9° E long. This means it's close to the sulfate deposit I mentioned at about 70°N lat., 230°E long.
Notice the image contains one and possibly two volcanic landforms. They might be the origin of the nearby sulfate deposits.
Bob Clark