The land of the Tyrrhena massif was what the areologists in the early years had called the “dissected unit” of the southern highlands, which was much the same as the “cratered unit,” but further broken by small channel networks. The lower and more typical highlands surrounding the massif also contained areas of “ridged unit” and “hilly unit.” In fact, as quickly became obvious the morning they drove out onto the land, all aspects of the rough terrain of the southern highlands were on view, often all at once: cratered, broken, uneven, ridged, dissected, and hilly land, the quintessential Noachian landscape. Sax and Nanao and Tariki sat on the observation deck of one of the Sabishii University rovers; they could see other cars carrying other colleagues, and there were teams out walking ahead of them. On the last hills before the horizon to the east, a few energetic people were fell-running. The hollows of the land were all lightly dusted with dirty snow. The massif was centered fifteen degrees south of the equator, and they got a fair bit of precipitation around Sabishii, Nanao said. The southeast side of the massif was drier, but here, the cloud masses pushed south over the ice in Isidis Planitia and climbed the slope and dropped their loads.

Indeed, as they drove uphill great waves of dark cloud rolled in from the northwest, pouring over them as if chasing the fell-runners. Sax shuddered, remembering his recent exposure to the elements; he was happy to be in a rover, and felt he would need only short walks away from it to be satisfied.

Eventually, however, they stopped on a high point in a low old ridge, and got out. They made their way over a surface littered with boulders and knobs, cracks, sand drifts, very small craters, breadloafed bedrock, scarps and alases, and the old shallow channels that gave the dissected unit its name. In truth there were deformational features of every kind to be seen, for the land here was four billion years old. A lot had happened to it, but nothing had ever happened to destroy it completely and clean the slate, so all four billion years were still there to be seen, in a veritable museum of rockscapes. It had been thoroughly pulverized in the Noachian, leaving regolith several kilometers deep, and craters and deformities that no aeolian stripping could remove. And during this early period the other side of the planet had had its lithosphere to a depth of six kilometers blasted into space by the so-called Big Hit; a fair amount of that ejecta had eventually landed in the south. That was the explanation for the Great Escarpment, and the lack of ancient highlands in the north; and one more factor in the extremely disordered look of this land.