It is easy to take modern geography for granted. The mountains and rivers we see on a daily basis seem so large and immovable that, on a human time scale, they may as well have always been there. But there is a great wealth of geologic history embedded in every one of those formations, and extracting that history is often as easy as looking at them with a keen eye. Many of the formations found here in Wyoming, such as the Medicine Bow Mountains, are composed of rock from more than two billion years ago. This rock was formed in a fault at the bottom of an ocean that would be unrecognizable in the modern era and was slowly pushed outward and upward by more rock forming from the same fault. We can tell that the mountains are made of metamorphic rock, meaning they were subjected to intense heat and pressure during the uplift that produced them. Most of the rock is quartzite, which would have been a pure quartz sandstone before the uplift. All of this can be observed without even digging into the rock, and it’s incredible how much history can be observed with the naked eye.
We can glean the history of more than just rocks, however, as many of these geologic formations also contain fossils from tens or hundreds of millions of years ago. The Spring Creek preserve, for example, features a series of formations from the cretaceous seaway, a period in which Wyoming was covered by a shallow sea. We can see the progression of life in the region within the fossil record, from well-preserved fish scales and bones in the shale of the Mowry Formation, to the sparsely populated volcanic ash of the Frontier Formation, to the explosion of life and biodiversity with fish scales, shark teeth, bivalves, and ammonites within the sandstone of the Wall Creek Member, to the vast layers of chalk in the Niobrara Formation made up almost entirely of surface-dwelling phytoplankton. We can use the color of the rock to determine the amount of organic carbon preserved in the formation, or other minerals like sulfur or iron. We can also make inferences about the amount of dissolved oxygen in the water and its salinity, which we can use to determine whether the water predominantly came from the north or south. The types of life forms in the fossil record allow us to make further inferences about the environment, and we can use all of this information to paint a complete picture of this region over the span of tens of millions of years.
Every mountain and river is trying to tell a story, it just takes the right listener to decipher it.