Obnoxiously...
I continue to maintain that Dr. Hartmann (and many others) have misidentified circular formations on the surface of Mars as impact craters. This may be especially true for small diameter circular formations (which are found in some areas at super-saturation densities.) There are many causes of circular formations on the surface of Mars, including impact, sub-surface collapse, and "bubbling" of heated surface materials in the cold near-vacuum of the atmosphere.
Yet since the earliest Mariners, almost all circular formations on Mars have been categorized as impact structures, with or without any supporting evidence. As the Martian Paradigm shifts again, I hope the diversity of circular formations is factored in.
Cheers, BFelix