United by an enormously ancient and eventful geological history, the Klamath- Siskiyou is divided by elevation, climate, and soils into a dazzling mosaic of natural worlds.

In the Beginning: Geology. The geological map of Oregon is a beautiful thing, with sweeps of color denoting the various types of rock making up the state. In most parts of the map, the pattern is fairly broad-brush, but one’s eyes are irresistibly drawn to the southwest corner, where the sweeping strokes break down into an fractured kaleidoscope of fiendish complexity. In the words of one despairing geologist, the mountains of the Klamath-Siskiyou are "a geological nightmare, a chaotic mixture of a wide variety of rocks originally formed at different times, in different ways, and at widely separated places all swept together into a hopelessly confused heap." The region owes much of its biological wealth to the age and complexity of its rocks.

The oldest rocks in the Siskiyous are thought to be about 425 million years old; that is, older than the emergence of life on land. Most of the rocks of the region are at least 200 million years old, and originated as offshore sediments that were repeatedly uplifted, folded, and mixed with granitic rock from the ancient seafloor bedrock. Intruding into this mixture are large blocks of rocks formed under extreme pressure in the earth’s interior: peridotite and serpentine. Because of the manner of their formation, these rocks are deficient in some minerals (including calcium and potassium) and are heavily laden with others (especially magnesium and iron). One of the largest blocks of such rocks in the world lies west of Cave Junction, and smaller outcrops occur throughout the Klamath-Siskiyou.

The strange mineral composition of serpentine and peridotite means that soils derived from them will be very inhospitable to plant life. On a landscape scale, the open Jeffrey pine woodlands northwest of Cave Junction reveal the struggle of trees to grow on serpentine, a struggle that has been won in the unique Redrock Rainforest of the Kalmiopsis Wilderness. On a more intimate scale, the tiny fens that dot Eight Dollar Mountain and other serpentine mountains throughout the region are treasure-troves of rare orchids, insect-eating cobra plants, and other unique species that have evolved the ability to survive where their more widespread rivals cannot. Our region is famous to botanists around the world for the amazing diversity of its serpentine-adapted plants. More generally, the wide array of soil types resulting from the mountains’ complex history provide plenty of opportunities for other plant species to put down roots in their favorite ground.