Old Ultramafic Soils with Ferruginous Black Nodules along the Western Margin of the Klamath Mountains, California and Oregon

The Klamath Mountains of the Mesozoic and early Cenozoic were reduced to a peneplain in the Miocene. Subsequently, the mountains have risen thousands of meters and been dissected by erosion. Along the western margin of the Klamath Mountains, in areas where the peneplain has not risen more than a few hundred meters, there are remnants of the peneplain with some very old ultramafic soils that have black, magnetic nodules in the surface horizons. Maghemite is the magnetic mineral in the nodules, although the soils have much more iron (Fe) in goethite. There is no more than a possible trace of any manganese oxide mineral in the nodules. The ferruginous nodules are in soils that are well drained and have reddish hues. There are nearly 50 thousand hectares of soils with black nodules in Klamath Mountains. They are in ferruginous Kanhapludalfs and Kandihumults, and a few hundred hectares of ferritic Kandihumults. Soils with ferruginous and ferritic black noddles are sparse in California, but common in ultramafic soils on islands in the Caribbean sea.