Region 4: The Cascade-Sierra Mountains

Permian-age rocks in the northern Cascades contain gastropods and corals, along with fusulinid foraminifera shells (Figure 3.22). Fusulinids are the rice-sized shells of single-celled, amoeba-like organisms that lived in huge numbers on the sea floor during the late Paleozoic.

Late Triassic rocks found in the Cascades and Sierra Nevada contain abundant ammonoids and nautiloids, as well as brachiopods and oysters. Jurassic rocks exposed in Stanislaus and San Joaquin Counties in central California indicate a coastal marine environment, with marine fossils including sea urchins, ammonoids, and bivalves. Terrestrial fossils are primarily plants such as cycads and ginkgos.

Figure 3.22: One-celled fusulinid shells from the Permian. A) A cluster of shells, the size and shape of large rice grains. B) Photograph of a cross section through a single fusulinid, as seen through a microscope.

Most Neogene fossils from the Cascades represent terrestrial forest and grassland communities. Fossil plants include petrified wood from willow, yew, swamp cypresses (Figure 3.23), and Metasequoia (see Figure 3.17). Fossil vertebrates are less common, but include rabbits, beavers, camels, and the extinct horses Parahippus, Archaeohippus, and Merychippus (Figure 3.24). Merychippus was about 90 centimeters (3 feet) tall and had three toes, as opposed to the single toe found in modern horses. It is also the first horse known to have primarily grazed on grasses, rather than to have browsed on shrubs, as earlier horses did.

Figure 3.23: Cross section of the permineralized trunk of a species of cypress (Taxodium) from the Miocene of Washington. About 0.3 meters (1 foot) in diameter.

Figure 3.24: A primitive horse, Merychippus. A) Skull, about 40 centimeters (16 inches) long. B) Reconstruction.