Hello Nick -

You have to remember that these guys have been sucking on the teat of watery Mars for over a century - If I remember right, Huxley pointed out that the physics of watery Mars were impossible in 1906 or 1909 or thereabouts...
It doesn't matter how many pictures come down, or samples are found - Lowell's vision of canals and an advanced civilization on Mars is still sub-conciously held by many, and there's a whole lot of other more "respectable" folks who are quite happy to make a living playing to it -
(I think of these "space enthusiasts" as "von Braun's children", but thankfully they're getting older and dying off, leaving space in the hands of the post-Mariner generation...)
So what do they want? Well, since you can't very well have CO2 filled canals feeding crops of popsicles, you're kind of stuck - best thing to do is to come up with an evolutionary history, go back to the watery age, and tell them where you think fossils might be according to your scheme -

EP - Back to the Moon, this time to stay:
http://www.geocities.com/epgrondine