Hawksbill Station by Robert Silverberg

Hawksbill Station by Robert Silverberg (Galaxy, August 1967) opens with Barrett, the “king” of Hawksbill Station surveying his empire, the late-Cambrian landscape. We learn that he is in his sixties and, although previously a physically imposing figure, an accident to his left foot (crushed in a rock fall) has left him a cripple. Then a man called Charley rushes over with the news that a prisoner is being sent back to them from the future.
As the pair go over to the dome to await the arrival of the new man, and discuss possible bunking arrangements for him, we learn that (a) Hawksbill Station is a penal colony for revolutionaries a billion years in the past and (b) several of the men at the station are psychologically unstable, a result of the one-way trip there (one of the men is trying to build a woman out of chemicals and dirt after a “homosexual phase”).
When the new prisoner arrives Barrett is surprised by how young he is, and they subsequently take the man, Hahn, to their doctor to deal with his temporal shock. En route, Barrett makes him look out the door of the building:

Hahn looked. He passed a hand across his eyes as though to clear away unseen cobwebs and looked again.
“A late Cambrian landscape,” said Barrett quietly. “This would be a geologist’s dream, except that geologists don’t tend to become political prisoners, it seems. Out in front is the Appalachian Geosyncline. It’s a strip of rock a few hundred miles wide and a few thousand miles long, from the Gulf of Mexico to Newfoundland. To the east we’ve got the Atlantic. A little way to the west we’ve got the Inland Sea. Somewhere two thousand miles to the west there’s the Cordilleran Geosyncline, that’s going to be California and Washington and Oregon someday. Don’t hold your breath. I hope you like seafood.”
Hahn stared, and Barrett standing beside him at the doorway, stared also. You never got used to the alienness of this place, not even after you lived here twenty years, as Barrett had. It was Earth, and yet it was not really Earth at all, because it was somber and empty and unreal. The gray oceans swarmed with life, of course. But there was nothing on land except occasional patches of moss in the occasional patches of soil that had formed on the bare rock. Even a few cockroaches would be welcome; but insects, it seemed, were still a couple of geological periods in the future. To land-dwellers, this was a dead world, a world unborn.  p. 121 (World’s Best Science Fiction 1968, edited by Donald A. Wollheim & Terry Carr)

Eventually Hahn recovers and they learn he is an economist. Barrett takes him to his new quarters and bunk mate, an old-timer called Latimer (who is trying to develop psi powers to get back to the future but is otherwise of sound mind).
That evening Hahn joins the rest of the prisoners for dinner, and they quiz him about the future (the prisoners refer to it as “Up Front”) and about himself. His answers are very vague however, and this makes Barrett suspicious—a plot thread that slowly develops over the course of the rest of the story. This eventually comes to a head (spoiler) when, after Latimer has confided his suspicions to Barrett about Hahn’s constant note taking, he is put under surveillance. Later Hahn is seen near the time machine and, after he initially can’t be found, is caught arriving back from the future. After Hahn is questioned it materialises that there has been a change of government in the future and they are looking to close the penal colony and rehabilitate the men; Hahn is there doing psychological assessments.
While this routine plot plays out there is much else that makes the story a good read. Apart from the character study of Barrett himself, the most senior of the prisoners (fifty earlier arrivals have died), we learn about (a) the future that has sent these men back in time, (b) the rough lives they live (partially as a result of the slightly random time shots early on in the project), (c) what the world is like in this era (there are evocative descriptions of a protean Earth), and (d) the toll on the men sent there (their psychological state is as bleak as the landscape).
All this is well done, and the tale’s only weakness is the slightly flat ending, which has Barrett fearing the thought of going back to the future—he offers to stay and and run the science station that it will become.
***+ (Good to Very Good). 18,100 words.