Image of Martian hemisphere centered on longitude 90. The physiographic provinces are indicated by shading and various symbols. Volcanic mountains are shown in black, with a "v". Olympus Mons in the large volcano centered at (about) latitude +15 and longitude 135, and the three other large volcanic mountains of the Tharsis ridge lie to the south and east. The starting with the southernmost, the names of these volcanic mountains are Arsia, Pavonis, and Aescraeus Mons. The younger terrain of the northern hemisphere is displayed as white, and the symbols indicate undivided plains (p), and volcanic plains (pv), which are plains whose origin is volcanic in nature. Valles Marineris is seen running from the Tharsis ridge eastward between -10 and -20 degrees south latitude. The impact basin centered at about -50 is Argyre.
Image of Martian hemisphere centered on longitude 270. The division between the old southern plains and the modified units of the north slopes down and to the right--it is the complement of that in the first figure. The large impact basis mapped as "p," undivided plains, is Hellas. Just north and east of Hellas is the a region marked "pc." This, and similar regions were at one time mapped into the so-called Hesperian system. Another area mapped into this system is centered at longitude 290, latitude +10. The region has very distinctive coloring, because it was one of the few consistent features that was seen on telescopic maps of mars. Other areas mapped into the Hesperian may be seen north and south of Valles Marineris on the image above this one. Mars was originally mapped into three main systems. The oldest was called the Noachian, with the prototype area to the west of Hellas. The youngest was called the Amazonian, named after a region just west of the Tharsis volcanos.