This first thing than leapt to my mind was the Devil's Tower, noted in this 1956 US issue. As a youth, when the movie Close Encounters of the Third Kind came out, my best friend and I felt in the know cause we both recognized immediately (way before Richard Dreyfuss' character) the geological feature thanks to our familiarity with this stamp which was in both of our collections. Scott 1084.
This Canada 2017 World Heritage Site stamp shows the Mistaken Point Formation, which contains one of the most diverse and well-preserved collections of Precambrian fossils in the world. Fossilized charnia is clearly visible on the outcrop.
Great subject!! although I don't collect stamps about geology, I have few in my paleontology collection, to illustrate several aspects in animal evolution. Part of them are about continental drift.
Alfred Lothar Wegener (1880 – 1930) was a German polar researcher, geophysicist and meteorologist. He is the originator of the theory of continental drift by hypothesizing in 1912 that the continents are slowly drifting around the Earth (Kontinentalverschiebung). In the 1950s, numerous discoveries provided strong support for continental drift, and thereby a substantial basis for today's model of plate tectonics.
Here are two stamps issued in 1980 by East Germany (DDR) and by West Germany for use in Berlin, to commemorate centenary of Wegener birth:
Gondwana is the name given to the more southerly of two supercontinents (the other being Laurasia) that existed from approximately 510 to 180 million years ago. Gondwana included most of the landmasses in today's Southern Hemisphere, including Antarctica, South America, Africa and the Australia, as well as the Arabian Peninsula and the Indian Subcontinent, which have now moved entirely into the Northern Hemisphere. Gondwana began to break up in the early Jurassic (about 184 Mya) due to continental drift.
Here is a set of six stamps entitled "Gondwana: continental drift and climate changes" issued on March 3, 1982 for use in British Antarctic Territory depicting the Gondwana break up and the position of the Antarctic in each time point. The stamp designs depicting the climate changes in Antarctic that have occurred over time. Note that the stamp colours reflecting the climate during the period the stamp depicting:
Canada 2019 From Far and Wide series Monoliths of the Mingan Archipelago in eastern Quebec: The entire island chain represents remnant of erosion of a thick limestone formation. Castle Butte in the Big Muddy Badlands in Saskatchewan: This free standing sandstone formation is a relic from the Ice Age.