GEOLOGY OF OREGON CAVES AND THE SURROUNDING KLAMATH MOUNTAINS

Oregon Caves National Monument and Preserve lays deep in the Siskiyou Mountains of Southwestern Oregon. The Siskiyou Mountains are a subsection of the larger Klamath Mountain Range that runs from southwestern Oregon and extends down into Northwestern California. These mountains were formed from multiple episodes of accretion along the Cascadia Subduction Zone over a span of approximately 380 million years. The geology of this area is complex because the rocks have been highly altered. The project goal for this Scientists in Parks position at Oregon Caves National Monument and Preserve, is to develop an educational curriculum that explains the regional geology of the Klamath Mountains and the formation of Oregon Caves. The program is targeted towards high school honors and college freshmen students, to provide them with an overview of accretionary terrain building and karst formation.

Oregon Caves are marble solution caves. The marble that makes Oregon Caves belongs to the Rattlesnake Creek Terrain of the Paleozoic – Triassic Belt of Klamath Mountain’s accretionary episode. This terrain contains a mélange of ultramafic to intermediate intrusive rocks, serpentines, volcanic rocks and a variety of sedimentary rocks. The limestone of this terrain has been metamorphosed to a low grade marble, which has been dissolved by the River Styx over a span of 2 million years, to form the Oregon Caves. Stitching plutons have intruded throughout the terrains of Klamath Mountains. The Greyback pluton has intruded into the Rattlesnake Creek Terrain, prior to its accretion, about 200 million years ago. A dike of this pluton can be seen in the largest room of the cave, the Ghost Room. The composition of this dike is tonalite. Further exposures of this pluton can be seen on Mount Elijah, which is one of the highest peaks on the preserve. Chert and argillite of this terrain are also exposed in various parts of the park.

An educational curriculum focused on the geology of the park and the surrounding Klamath Mountains will be a useful resource to further aid the visitor experience by allowing them to get a brief geologic overview of the region. It will also provide visitors and locals with a more engaging way to learn the complex regional geology. This curriculum, once finished, will be available on the park’s official website.