undifferentiated rock units

Paleontology and geology

Outcrops of Triassic rocks occur in two areas of Idaho. One is in the accreted terrane along the border with Oregon and southern Washington. These deposits consist of metamorphosed volcanic and sedimentary rocks that have yielded a variety of marine fossils, primarily from adjacent areas of Oregon. These include ammonites, bivalves, gastropods, sponges, echinoids, corals, bryozoans, corals, and brachiopods. In southeastern Idaho, Triassic deposits (shown as undifferentiated on this map) are largely marine sedimentary rocks. Fossils are generally sparse except for the Thaynes Formation, which contains fossils of bilvalves, gastropods, ammonites, crustaceans, shark teeth, crinoids, brachiopods, fish, microfossils, and fragmentary remains of an early ichthyosaur. The presence of redbeds and thin coaly layers indicate some terrestrial deposition.