Free Space Prison (originally published as "The Survivors") by Tom Godwin

the distance, to pour out a cloudburst. The 1.5 gravity gave the wall of water that swept down the canyon a far greater force and velocity than it would have had on Earth and boulders the size of small houses were tossed into the air and shattered into fragments. But all the rain fell upon the one small area and not a drop fell at the caves.
      One single factor was in their favor and but for it they could not have survived such intense, continual heat: there was no humidity. Water evaporated quickly in the hot, dry air and sweat glands operated at the highest possible degree of efficiency. As a result they drank enormous quantities of water—the average adult needed five gallons a day. All canvas had been converted into water bags and the same principle of cooling-by-evaporation gave them water that was only warm instead of sickeningly hot as it would otherwise have been.
      But despite the lack of humidity the heat was still far more intense than any on Earth. It never ceased, day or night, never let them have a moment's relief. There was a limit to how long human flesh could bear up under it, no matter how valiant the will. Each day the toll of those who had reached that limit was greater, like a swiftly rising tide.
      There were three hundred and forty of them, when the first rain came; the rain that meant the end of summer. The yellow sun moved southward and the blue sun shrank steadily. Grass grew again and the woods goats returned, with them the young that had been born in the north, already half the size of their mothers.
      For a while there was meat, and green herbs. Then the prowlers came, to make hunting dangerous. Females with pups were seen but always at a great distance as though the prowlers, like humans, took no chances with the lives of their children.
      The unicorns came close behind the first prowlers, their young amazingly large and already weaned. Hunting became doubly dangerous then but the bowmen, through necessity, were learning how to use their bows with increasing skill and deadliness.
      A salt lick for the woods goats was hopefully tried, although Lake felt dubious about it. They learned that salt was something the woods goats could either take or leave alone. And when hunters were in the vicinity they left it alone.
      The game was followed for many miles to the south. The hunters returned the day the first blizzard came roaring and screaming down over the edge of the plateau; the blizzard that marked the beginning of the long, frigid winter. By then they were prepared as best they could be. Wood had been carried in great quantities and the caves fitted with crude doors and a ventilation system. And they had meat—not as much as they would need but enough to prevent starvation.
      Lake took inventory of the food supply when the last hunters returned and held check-up inventories at irregular and unannounced intervals. He found no shortages. He had expected none—Bemmon's grave had long since been obliterated by drifting snow but the rope still hung from the dead limb, the noose swinging and turning in the wind.
     
      Anders had made a Ragnarok calendar that spring, from data given him by John Prentiss, and he had marked the corresponding Earth dates on it. By a coincidence, Christmas came near the middle of the winter. There would be the same rationing of food on Christmas day but little brown trees had been cut for the children and decorated with such ornaments as could be made from the materials at hand.
      There was another blizzard roaring down off the plateau Christmas morning; a white death that thundered and howled outside the caves at a temperature of more than eighty degrees below zero. But inside the caves it was warm by the fires and under the little brown trees were toys that had been patiently whittled from wood or sewn from scraps of cloth and animal skins while the children slept. They were crude and humble toys but the pale, thin faces of the children were