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Geology and Soils
One way to start exploring the diversity of an area is by looking at the rocks. Rocks can tell you a story about how an area was formed and will determine what plants grow there. Most rocks we see today were once a flowing liquid below the earth’s surface. During their journey upward they hardened and 
appeared on the surface in a rainbow of colors. Rocks complete a cycle just like plants and animals do, and will eventually break down into soils which plants will use to grow. Rocks can contain fossils letting us know who lived there before us, and have shaped the landscape of the Klamath Region we see today. The geologic history of the Klamath Region can be told using two stories: the forming of the Klamath and Siskiyou Mountains, and the forming of the Cascades.
Much of the Klamath and Siskiyou mountains are composed of rocks originally found on the bottom of the ocean. How did rocks on the bottom of the ocean get to the top of a mountain? Around 200 million years ago the continent of North America collided into the ocean floor in the Pacific. As the North American continent slowly moved over the oceanic floor, it scraped off pieces of the surface of the sea floor, like scraping off butter with a knife. This repeated scraping of oceanic floor mixed with rocks from the North American continent, created the variety of rocks we see today in the Klamath and Siskiyou Mountains. Further changes in rock formations due to weather and plate shifting has created a region often referred to as the “Klamath Knot.” This intricate tangle of ancient rocks produces a variety of soils which support the large diversity of plants species famous in this region.
The Cascade Mountains and Modoc region, in contrast tell a whole different story because they are 
volcanic landscapes. Picture huge eruptions and molten lava flowing over the land forming deep lakes, inverted volcanoes and lava tubes. The Cascades were formed from lava originating deep (up to 60 miles deep!) in the earth’s mantle. When the North American continent moved over the ocean floor, it pushed it downward under the earth’s surface. The rocks forming the surface of the ocean floor melted and this molten lava then returned to the earth’s surface forming volcanoes. The Cascade Range in this area includes a number of majestic peaks including Mount Mazama, which formed Crater Lake, Mt. McLoughlin, Mt. Shasta, and the unique Lassen Peak. Basalt lava flows on the eastern side of the Cascades formed lava tubes and unique rock structures characterizing Lava Beds National Monument. Although fascinating and diverse in form, the volcanic rock of the Cascades Modoc subregion is much younger and less varied than in the Klamath and Siskiyou Mountains.
Learn more about geology and soils by clicking on the links below:
Photos: Lassen Peak, Gladys Lucille Smith © California Academy of Sciences
Crater Lake NP | Oregon Caves NM | Redwood NP | Lassen Volcanic NP
Whiskeytown NRA | Lava Beds NM | NPS Klamath Network | SOU Home
An Outreach and Education Project made possible by the National Park Service, Klamath Network Inventory and Monitoring and Southern Oregon University
