Fredonyer Pass is part of the approximate boundary between the Sierra Nevada and the Cascade Range. This irregular boundary is sometimes defined as the southern extent of Cenozoic igneous surface rock from the Cascade Range. This boundary roughly follows the drainage of the North Fork Feather River southeast to Fredonyer Pass. Note that there are other Cenozoic igneous rocks in the Sierra (e.g., near Lake Tahoe), but there is a clear geological division near Fredonyer Pass, and points westward as far as the Sacramento Valley.