The Sonoma orogeny was one of a sequence of accretionary events along the Cordilleran margin, possibly caused by the closure of the basin between the island arc of Sonomia and the North American continent.
[9][10] These units consist of basalt, felsite, bedded chert, limestone, and detrital rocks ranging from conglomerate to argillite[11] that accumulated in a trough west of the Antler orogenic belt.
The Sonoma orogeny involved closure of this basin and a process by which the blanket of oceanic sedimentary rocks (the Havallah sequence) was obducted onto the continental shelf via the Golconda thrust.
[11] Brueckner and Snyder expressed some uncertainty about the exact time of final emplacement of the allochthon, but emphasized that structures associated with the Sonoma orogeny had a long history from the middle Paleozoic to the Permian-Triassic periods.
In the East Range just to the west of China Mountain, Whitebread mapped the contact between strata of Permian age, at the top of the Havallah, and the base of the overlying Koipato as parallel, indicating a lack of evidence for an orogeny at the Permian-Triassic boundary.
[7] Ketner's work denied the oceanic origin of the Havallah and related sequences, eliminated the necessity for convergent plate tectonics and a far-traveled allochthon, established the age of the Golconda thrust as post-Triassic, and cast doubt on the very existence of the Sonoma orogeny.