Stu, 1 cm, impossible, then closer to 1 meter is the most likely. Thanks to Nep, Stu and The other Doug.
The other thing, about after interpreting the picture, what I was thinking that the surface must be somewhat wet (ending the spring and some water might have sublimated?? and the other part might have drought into the surface??). The surface aspect is smooth probably by the ice weight and by the water erosion and the surface have no white color, then no snow??. This contradicts to Planetary blog (Phoenix on Course for Mars Landing) which says that the zone landing surface will be covered by ice.
"Our landing area has the largest concentration of ice on Mars outside of the polar caps. If you want to search for a habitable zone in the arctic permafrost, then this is the place to go," said Peter Smith, principal investigator for the mission, at the University of Arizona, Tucson.
Finally, I am preoccupied about the success of landing since the ellipse landing is so big (the landing area is an ellipse about 100 kilometers (62 miles) by 19 kilometers (12 miles)). Indeed, according to the Phonix Web page says:
the sophisticated landing system on Phoenix allows the spacecraft to touch down within 10 km (6.2 miles) of the targeted landing area.
On the other hand, I have heard that the intelligent discrimination among boulders was deactivated in order to avoid a major complication in deciding rightly the landing site. Although I have found a quote from Phoenix's Arizona's Web which says:
Besides, the Phoenix's navigation system is capable of detecting and avoiding hazards on the surface of Mars.