Stratigraphy
The sequence caught up in the Sonoma orogeny consists of thick Mississippian through Permian marine deposits including chert, limestone, conglomerate, siltstone, shale, lava flows and pyroclastics that accumulated in a trough west of the Antler orogenic belt. The majority of beds were deposited along the Golconda thrust, at least 60 miles (100 km) eastward or inboard of the new continental margin. Segments of accreted Permian island arcs, composed of volcanic and volcaniclastic strata and paired geotectonically with Sonoma accretionary prisms to the east, are present in the Klamath-Sierran region of the Cordilleran orogen to the south of volcanic cover in the Pacific Northwest.
Read more about this topic: Sonoma Orogeny