undifferentiated rock units

Paleontology and geology

A shallow sea covered parts of Idaho during the Cambrian. Major outcrops of shallow marine sediments are found along the eastern and southern margins of the state (included as undifferentiated on this map). The northernmost ones are metamorphosed and yield only a sparse fauna, mostly trilobites and brachiopods. In the south, fossils of these organisms are far more abundant and varied; hyolithids, worm tubes, and fragments of large predaceous crustaceans have been found.