High Quality Content by WIKIPEDIA articles! The Sonoma orogeny was a period of mountain building in western North America, which occurred during the Permian / Triassic transition, around 250 million years ago. Following the Late Devonian Antler orogeny, it was the second major accretionary event along the Cordilleran margin with many more to come as the closure of the basin between the island arc of Sonomia and the North American continent. Evidence of this event can be seen throughout western North America, but most distinctly in northwest Nevada.