Post-apocalyptic story: Civilization destroyed, Liberian survivors travel by airship to Denver and find a giant cube

Question

This is a post-apocalyptic story I think I read in Analog magazine.

It's illustrated on the first and second page of the story, showing an airship with a ladder let down, and people standing in front of an enormous cube.

The plot was that there was a/the Godsoul comet that (almost?) collided with earth. Most of civilization was wiped out and most of the world's land flooded. Their spirits (called piquinoes by the Liberians and worshiped as ancestors) are still around. The protagonist lives in Liberia, and he and a crew mount an expedition in a zeppelin-like craft to visit the city of Denver. They find nothing except a white cube enclosing most of the remains of the city. They get inside and have have to deal with the Grey Men, who are the result of using a teleportation system to deal with the racial crisis. They have also produced the spirits as a byproduct.

Eventually, a member of their party uses the teleportation system to turn Jupiter into a new sun by making a connection to an antimatter universe.

The protagonist has been caught in the transport system. The backlash also destroys the new cube city and his body. He returns to Liberia and makes plans to revitalize society as a piquino.

Answer 1

It's Topeka, not Denver, but otherwise this is "All Which It Inherit" (1974) by Bernard Deitchman, published only (so far) in Analog, September 1974.

The story starts out in (New) Monrovia, Liberia where a crowd of people fill a square all whispering to their fetishes. The fetishes, piomdos, apparently contain spirits that speak to the people:

Prospero, the man for our season, Massaqoui thought. His island was no more enchanted than our country. But the spirits in the piomdos, in the fetishes, showed no inclination to melt into thin air.

Godsoul was a comet-like body that has devastated much of the Earth:

Godsoul: heat that freed water from the ice caps, and earthquakes that wrinkled and split the skins of the continents; Europe sent to a watery grave unmarked except for the tips of a few mountains; new land raised in the re-formed Atlantic, freshly-exposed seabed scattered with the remains of Godsoul itself.

Godsoul: the comet that blossomed out of Jupiter; many times the size of Earth, it trailed its guts across the sky and shrank to a whisper of itself before exploding across the North Atlantic. But even then it was an enormous whisper, one that spread twenty billion tons of debris over an area of fifty million square miles.

The airship Liberia is sent to America, because the spirits seem to be encouraging that. When it reaches Topeka, they find the cube and an alcove labeled with

THE CITY OF TOPEKA WELCOMES
The Wayfaring Stranger.
Press button to enter. We reserve the right to refuse entry to anyone.

When Massaqoui enters he is shunted to a room where it is explained that the teleportation system (called "the Quickie") can rewrite who he is, and he is "offered" the chance to be made white in order that everyone in US society should match.

"But the Quickie can solve these problems, difficult as they have been, because it can make you, and all other black people, white.

"Understand me: we can alter the patterns of information we receive from your body when you enter the Quickie. In this way we can change your physical characteristics to anything we want. We could make you purple or green when you leave, but what we offer is to make you white."