This is the free portion of the full article. The full article is available to licensed users only.
How do I get access?



The middle of three systems (of time-stratigraphic units) or periods (the chronologic equivalents to systems) in the Martian stratigraphic scheme, named after the region of Hesperia Planum (Hesperia: "The Occident"; see U.S. Geological Survey Gazetteer of Planetary Nomenclature). Depending on the different