Situated about 20 miles from the town of Cave Junction, Oregon, USA is the Oregon Caves National Monument. Discovered in 1874 by local hunter Elijah Davidson, the caves became a tourist destination in the late 1800s. In 1909 US President William H Taft established the caves as a National Monument, which was operated by the US Forest Service until 1933 when the National Park Service took over management. One of the first permanent buildings to be erected was the Chalet, which was built in 1924 and is now the Visitor's Center. During the great Depression of the 1930s, the Civilian Conservation Corps made many improvements to the tour route inside the caves as well as the grounds outside.
The Klamath Mountains
The Oregon Caves lie within the Siskiyou Mountains of Southern Oregon. Geologically, these ranges are known as the Klamath Mountains and are one of the three oldest mountain ranges in Oregon. The Klamaths were part of the Sierra-Nevada chain until they broke off about 150 million years ago and drifted approximately 60 miles west from the continent to become an island. During this period the island shifted from a north-south position to an east-west position where it once again began to collide with the North American Plate.
As the Klamaths merged back into the continent, they pushed up ahead of them layers of calcite and silica rich mud that would later become the primary rock by which the caves would form. Large deposits of ultra mafic mantle rock were also compressed and uplifted into the older granites and schist from the continent to create a geologically diverse mountain range that runs along the coast of Northern California to just south of the city of Eugene, Oregon, USA.
Rocks & Minerals of the Area
A mixture of geological formations in the Klamaths provide the Oregon Caves as well as the surrounding area with an abundance of unique rocks and minerals. Folded and weathered marble is found throughout the caves, while deposits of diorite, gabbros, shale, graywacke, greenschist and amphibolites can be found all within a 75 mile radius.
Minerals such as actinolite, chromite and manganese are prevalent in specimens of jade and rhodonite, which can be found in the streams and hillsides 5-7 miles south of the monument's boundaries. Small grossular garnets can be found in mica schist formations 20 miles to the southeast, while serpentinite, talc, magnetite and hematite are common in the regions 30 miles west of the caves.
How the Caves Were Formed
The foundation for the caves began about 220 million years ago when tectonic movement by the Pacific and North American plates created an ocean basin along the Northwest coastline. The remains of sea life from the Triassic through the Cretaceous periods decomposed on the sea floor over millions of years to become compacted layers of limestone and chert. These layers were eventually dredged up and pushed into the continental rock when the detached Klamath Mountains reunited with the North American Plate.
Intrusions of plutonic rock created heat and pressure to transform the limestone into marble. Concentrations of carbon dioxide in the ground water created carbonic acid, which found its way through fractures and faults within the rock and over time dissolved the marble and limestone to create cavities and tunnels within the rock. Around 10,000 years ago, enough surface erosion had taken place to expose the caves to the outside environment.
The Geology of the Caves
The Oregon Caves are considered a single cave system with a series of chambers and tunnels that formed over an immense period of time. The structure sits on the edge of a quartz-diorite batholith that intruded into the system during its formation. Igneous, metamorphic and sedimentary rock from six rock-building processes can all be found within the system. Foliated marble formed by both contact and regional metamorphosis can be viewed in the outer areas of the caves.
A dike of quartz-diorite (Intrusive Igneous) runs through the ceiling of one of the larger chambers. Layers of compacted ash from Cascade volcanic activity (extrusive Igneous) are found in areas where it filtered in through faults in the rock. Clastic sedimentary breccias formed by erosion and bonded together by calcite can be found close to the entrances. Lastly, the caves are abundant with chemical sedimentary rock in the form of flowstone, dripstone, stalactites and stalagmites that make up the inspiring structures that people the world over come to view.
The Future of the Region
The Oregon Caves undergo extensive restoration a few times a year. With over 83,000 visitors in 2010, the caves suffer damage from clothing lint and skin oils. The lint and oil eat away at the structures, weakening them and causing breakage. Each year the staff and volunteers go throughout the cave to clean the debris. Maintaining public access while preserving the fragile ecosystem can often present some challenges. These are some of the problems facing the Klamath Mountains in the 21st century. A balance needs to be found where the environment of this remarkable region can be protected, yet its resources can be utilized and enjoyed by everyone. The Oregon Caves are just a page in earth's geologic history, but it is a fascinating one and the story isn't finished yet.
Sources:
Oregon Caves National Monument, US Department of the Interior, National Park Service, (Sept-2010)
Alt, David D, and Hyndman, Donald W. Roadside Geology of Oregon
Missoula, Montana, Mountain Press 1978
Covington, Sid, Oregon Caves National Monument Geologic Resources Management Issues and Scope Summary. Geologic Resources Division, US Department of the Interior, (Sept-2004)
David Katski - David Katski is a graphic designer with over six years experience in both print and web design. Holding and AS degree in the field of ...
Join the Conversation