TSR made extensive use of mock-up cover image art for catalogs and advertising.

In the 1992 Spring/Summer Catalog, TSR used a mock-up image for Gamma World, 4th edition.

Gamma World 4th mock cover 1992 Catalog
Mock-up vs Final Covers: Gamma World, 4th Edition

EDIT Nov 2019

Had a GW4 rulebook come through the shop, snapped some photos of that wonderful detachable poster map that is found inside the back cover.

Lake Geneva location-001
I was asked where Lake Geneva would be on the map. Here’s the best I could come up with. Maybe a local resident can do better.

Gamma World RPG at our reference site

Gamma World in stock in the shop

Gamma World 4th edition reprint and PDF available at DriveThruRPG

Check eBay

See Also:

Aliens and the Cryptic Alliances (GAMMA WORLD)

Aftermath RPG box set – early Phoenix Games edition

Gamma World colored map

Original Gamma World maps

Gamma World: Damaged inside the shrinkwrap