re: Contours? did someone say contours?
The 'ponding' in Margaritifer (along with possible long periods of precipation) owes much to the Tharsis Trough. There must have been flooding in the area... long standing body of water. Then there's that line of cliffs at Meridiani. The assumptions of Grant, Carr, Tanaka, Christensen and Squyres, et al. could be right after all, imho.