If we travel even further west, we have Sierra National Forest. When it was named a national forest in 1893, it was the second national forest in California and the largest one at the time. Located on the western slope of the Sierra Nevada Mountain Range, the land is full of thickly forested rolling hills, while some regions feature a tundra landscape. Lying within the Sierra Nevada range, the forest and the mountains share a geological history that began roughly 40 million years ago. (While this may sound like a long time ago, the formation is actually relatively young compared to the 4.5 billion years that Earth has been around!)
The mountains were formed from granitic rocks, which is a type of volcanic rock that develops when molten lava from the Earth’s mantle travels through the crust and is released at the surface — think volcanoes! The lava cools and hardens soon after being exposed to the Earth’s surface, whether it be the air or the bottom of an ocean. The solidified lava rock forms a hill shape, getting bigger and taller as more lava breaks through, travels to the top of the hill, pours down the edges and hardens on top of them. Eventually, these lava rock hills become mountains, and some become volcanoes that are still here millions of years later.
How did these old (or not-so-old) rocks become forests, though? This is where soil comes into the picture. The soil of each forest is unique; it forms from the parent rock, or the bedrock, which is buried deep into the earth and has weathered and made its way up to the surface as small grains. The bedrock is weathered by chemical reactions, biological processes (involving creatures working their way through the ground) and physical influences such as wind and sun. As it breaks up into smaller grain sizes, it makes its way up to the surface where it becomes moist from rain and fertile from the minerals and nutrients it’s exposed to. The many layers of soil are constantly changing, and the forests they support allow for the organic matter that they need to stay dynamic and fertile.
These fascinating tales only scratch the surface of our forests’ formations and the dense histories of the lands beneath them. The many kinds of rocks, orientations of rock formations, and hundreds of millions of years during which all these rocks were changing provide a biography of everything we see on Earth’s surface today. Understanding how your favorite forest came to be and everything it went through to exist can make it even more valuable to you, so don’t let your knowledge of forest formations end here. Keep searching for the hidden histories of all the forests and natural areas you love.