Marginal basin flysch deposits of the western Jurassic belt of the Klamath Mountains were thrust eastward beneath the western Paleozoic and Triassic belt during the Late Jurassic Nevadan orogeny. Nevadan underthrusting created two generations of nearly coaxial north-trending folds within the western Jurassic belt rocks. These structures formed at chlorite-grade, greenschist-facies conditions and have accompanying pressure solution and mineral recrystallization. The geometry of the Nevadan structures suggests that the thrusting direction was roughly west–east in present coordinates. This direction is perpendicular to the regional strike of the bounding thrust faults and is consistent across 35 km of dip exposure. Post-Nevadan structures include locally developed strike-slip faults and related third- and fourth-generation folds. These features have associated quartz and calcite veins but lack the metamorphic mineral growth associated with the Nevadan structures. Relatively young, high-angle normal faults are very common and appear to be contemporaneous with Neogene uplift of the entire range. Nevadan-age structures within the western Sierra Nevada Foothills terrane also formed in response to west–east thrusting. Global plate-circuit models suggest that the Nevadan Farallon–Pacific relative motion may have been orthogonal to the continental margin at the latitude of the Klamath Mountains. This convergence direction and the kinematic analyses suggest that the Klamath Mountains and Sierra Nevada Foothills were in their same relative orientation during the Nevadan orogeny.

Abstract For at least 13 000 years, California Indians mined and worked obsidian, trading the precious volcanic glass near and far, including obsidian and its uses in their everyday lives and beliefs. The cultural importance of obsidian is emphasized by the fact that a number of tribal groups created myths specifically about obsidian. Not only do the myths illustrate tribal religious beliefs, they help to trace geological and archaeological histories, as well. That obsidian still plays economic, artistic, and religious roles in the lives of today’s Californians offers testimony to its qualities the Indians discovered long ago.