Midway across Acidalia they began running into  long, straight, steep-walled, flat-bottomed canyons.  They looked, as George noted more than once, like the dry beds of the legendary canals.  The geological name for them was fossae, and they came in clusters.  Even the smallest of these canyons were impassable to rovers, and when they came on one they had to turn and run along its rim, until its floors rose or its walls drew together, and they could continue north over flat plain again.

The horizon ahead was sometimes twenty kilometers off, sometimes three.  Craters became rare, and the ones they passed were surrounded by low mounds that rayed out from the rims: splosh craters, where meteors had landed in permafrost that had turned to hot mud in the impact.  Nadia's companions spent a day wandering eagerly over the splayed hills around one of these craters; the rounded slopes, Phyllis said, indicated ancient water as clearly as the grain in petrified wood indicated the original tree.  By the way she spoke Nadia understood that this was another of her disagreements with Ann; Phyllis believed in the long wet past model, Ann in the short wet past.  Or something like that.  Science was many things, Nadia thought, including a weapon with which to hit other scientists.

Further north, around latitude 54°, they drove into the weird-looking land of thermokarsts, hummocky terrain spotted by a great number of steep-sided oval pits, called alases.  These alases were a hundred times bigger than their terran analogues, most of them two or three kilometers across, and about sixty meters deep.  A sure sign of permafrost, the geologists all agreed; seasonal freezing and thawing of the soil caused it to slump in this pattern.  Pits this big indicated that water content in the soil must have been high, Phyllis said.  Unless it was yet another manifestation of martian times scales, Ann replied.  Slightly icy soil, slumping every so slightly, for eons.

Irritably Phyllis suggested that they try collecting water from the ground, and irritably Ann agreed.   They found a smooth slope between depressions, and stopped to install a permafrost water collector.  Nadia took charge of the operation with a feeling of relief; the trip's lack of work had begun to get to her.  It was a good day's job:  she dug a ten-meter long trench with the lead rover's little backhoe; laid the lateral collector gallery, a perforated stainless steel pipe filled with gravel; checked the electric heating elements running in strips along the pipe and filters;  then filled in the trench with the clay and rocks they had dug out earlier.

Over the lower end of the gallery was a sump and pump, and an insulated transport line leading to a small holding tank.  Batteries would power the heating elements, and solar panels charge the batteries.  When the holding tank was full, if there was enough water to fill it, the pump would shut off and a solenoid valve would open, allowing the water in the transport line to drain back into the gallery, after which the heating elements would shut off as well.