Geology on the Trails

The components of geology, the science of the planet and its history, are always underfoot. But the geology is not always visible, and even when it is visible, it doesn't always reveal itself in a way that can be interpreted. In fact, one of the greatest mysteries facing us is how the planet has changed over geologic time (USGS). Here and there we find pieces of the puzzle that help to tell the story, places where the evidence can be seen a little more clearly than usual. So what kind of evidence can you see by getting out and going for a walk? The outline below provides an answer to that question.

Glaciation - the earth cycles through cold and hot periods over time. During the cold periods, ice sheets form and move over continents. Glaciers are powerful erosional forces. They leave a great deal of evidence behind after they are gone.

Earthquakes - when stresses in the earth's crust build to a point where the earth moves in response, you get an earthquake. This occurs frequently along the boundaries of tectonic plates, such as on the west coast of California where the North American Plate and the Pacific Plate meet.
Mining - Mining involves not only extracting precious resources from the earth but also figuring out where to find them and how they came to be there. The process of mining leaves plenty of evidence behind.
Erosion - the process of wearing down surface features through wind, ice, and water action, and sometimes through root invasion by plants. Although this is happening on a continuing basis, over long periods of time erosion can create fascinating displays and is very often the leading cause of some of our most treasured natural landscapes.
Volcanoes - these can be classic cones that erupt or fissures in the surface of the earth that allow magma to escape.

Ubehebe Crater in Death Valley

Geothermal Activity - water heated by
magma below ground escapes to the surface in a variety of forms, giving evidence that magma is relatively close to the surface in those hot spots.
Caves - a cave is simply a hole in the ground which may or may not have an opening to the surface. Naturally-occurring caves are formed by lava (see lava tubes) or water.
Fossils - the evidence left behind by plants and animals that lived long ago. The hard parts, and sometimes softer parts, were covered by sediment and turned to stone over a long period of time. The locations and types of fossils found in a particular place can give science invaluable information about the history of the place.

Geologic Terms Glossary
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