Klamath Mountains, Domain 5

Abstract

Domain 5 has mountains on the west aligned in broad arcs; in the eastern Klamath Mountains this arcuate pattern is not as evident. The outer arc curves from the triple junction of the California Coast Ranges, Great Valley, and Klamath Mountains in western Tehama County around through Del Norte County, where it is within a few kilometers of the Pacific Ocean, to Douglas County in Oregon. This western edge of the Klamath Mountains marks a boundary with the California Coast Ranges. The eastern edge of the Klamath Mountains forms a boundary with the Cascade Mountains. The southern, or southeast, boundary is where sediments of the Great Valley lap over the Klamath Mountains in Shasta and western Tehama counties. Serpentine rocks are more extensive in the Klamath Mountains than in any other domain or physiographic province in North America. Through the middle of the Tertiary, the Klamath Mountains were eroded to a nearly level plain called the Klamath peneplain (Diller 1902). According to Diller, the Klamath peneplain and the submerged coastal area that had been accumulating sediments were uplifted slightly during the Miocene, and erosion reduced the northern California Coast Ranges to a nearly level plain which he called the Bellsprings peneplain, noting that it is practically continuous with the Klamath peneplain. Subsequently discovered sediments of the Weaverville formation were deposited in a depression, or graben, in the Klamath Mountains during the Oligocene, indicating that uplift of the Klamath peneplain must have begun during the Paleogene, before the Miocene. Uplift was intermittent, allowing time for the erosion of broad valleys in less resistant rocks between episodes of uplift. Concordant summits, or mountains with summits of nearly equal elevation, are the evidence that led Diller (1902) to suspect a former peneplain. Although the mountain summits in any particular area are nearly equal or subequal, there is a general increase in summit elevation from the coast inland to 2.5–2.7 km. The altitude of Mt. Eddy on the eastern edge of the Klamath Mountains is 2751 m and that of Mt.