Photograph of a portion of a fossil cycad leaf from the Early Cretaceous of Washington. The leaf has a central axis and lateral leaflets that are elongated, narrow, and strap-like.

Fossils of the Cascade-Sierra Mountains

Simple map identifying the Cascade and Sierra Mountains physiographic region of the western United States.

Page snapshot: Introduction to the fossils of the Cascade-Sierra Mountain region of the western United States.

Topics covered on this page: Paleozoic fossils; Mesozoic fossils; Triassic marine fossils; Cretaceous plant fossils; Cenozoic fossils; Paleogene fossils; Neogene fossils; Resources.

Credits: Most of the text on this page comes from "Fossils of the Western US" by Brendan M. Anderson, Alexandra Moore, Gary Lewis, and Warren D. Allmon, chapter 3 in The Teacher-Friendly Guide to the Geology of the Western US, edited by Mark D. Lucas, Robert M. Ross, and Andrielle N. Swaby (published in 2014 by the Paleontological Research Institution; currently out of print). The book was adapted for the web by Elizabeth J. Hermsen and Jonathan R. Hendricks in 2022. Changes include formatting and revisions to the text and images. Credits for individual images are given in figure captions.

Updates: Page last updated September 1, 2022.

Image above: Portion of a cycad leaf (Pseudocycas insignis) from the Early Cretaceous Winthrop Formation, Washington. Photo of YPM PB 160796 by Yale Peabody Museum of Natural History, Division of Paleobotany, Yale Peabody Museum 2015 (CC0 1.0 Universal/Public Domain Dedication, accessed via GBIF.org).

Paleozoic fossils

Permian-age rocks in the northern Cascades contain gastropods and corals, along with fusulinid foraminifera shells. 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.

Mesozoic fossils

Triassic marine fossils

Triassic rocks found in the Cascades and Sierra Nevada contain abundant ammonoids and nautiloids, as well as brachiopods and oysters. These occur, for example, in Shasta County near the border between the Cascade-Sierra Nevada and Pacific Border Regions. For more information, see Fossils of the Pacific Border.

2-panel image showing Thalattosaurus alexandrae, a marine reptile from the Triassic of California. Panel 1: Drawings showing two views of the skull, from above and from the side. The skull is narrow and elongated with short, pointed teeth. Panel 2: Illustration of the live animal. The animal appear lizard-like with four limbs and a long tail flattened vertically. It is shown swimming in the water.

Thalattosaurus alexandrae, an extinct reptile named Annie Alexander, an heiress who financed the creation of the University of California Museum of Paleontology. Left. Drawings of the skull. Source: Merriam (1905) Memoirs of the California Academy of Sciences, vol. 5 (Wikimedia Commons). Right: Reconstruction of the living animal by Nobu Tamura (Wikimedia Commons, Creative Commons Attribution-ShareAlike 4.0 International license, image cropped).

Cretaceous plant fossils

The Early Cretaceous Winthrop Formation in Okanogan County, Washington, preserves a diversity of plant fossils. These include horsetails, ferns, cycads, cycadeoids, ginkgoes, pteridosperms (seed ferns), and conifers.

Photograph of a fossil horsetail stem from the Early Cretaceous of Washington. The stem is oriented horizontally in the image. It shows the jointing typical of horsetail stems, as indicated by horizontal lines or bands at intervals along the stem.

An ancient horsetail stem (Neocalamites vaganta) from the Early Cretaceous Winthrop Formation, Washington. Image of YPM PB 160766 by Yale Peabody Museum of Natural History, Division of Paleobotany, Yale Peabody Museum 2015 (CC0 1.0 Universal/Public Domain Dedication, accessed via GBIF.org).

2-panel image of photos of fossil fern leaves from the Early Cretaceous of Washington. Panel 1: Fronds from a member of the royal fern family. Each frond has a central rachis with lateral pinnae, each bearing pinnules (leaflets). Panel 2: Frond of a member of the forking fern order, with a central rachis and lateral pinnae, each bearing pinnules.

Fern fronds (leaves) from the Early Cretaceous Winthrop Formation, Washington. Left: A frond from a member of the royal fern family (Cladophlebis methowensis, Osmundaceae). Right: A frond (Calcaropteris boeselii) from a member of the order Gleicheniales, which includes the forked ferns and umbrella ferns. Images of YPM PB 160775 and YPM PB 160726 by Yale Peabody Museum of Natural History, Division of Paleobotany, Yale Peabody Museum 2015 (CC0 1.0 Universal/Public Domain Dedication, accessed via GBIF.org).

2-panel image of photos of fossil confer branches with leaves from the Early Cretaceous of Washington. Panel 1: Part and counterpart fossil showing delicate branches of an ancient conifer. Panel 2: Part and counterpart of a single branchlet with flat, needle-like leaves.

Conifer branchlets and leaves from the Early Cretaceous Winthrop Formation, Washington. Left: Sphenolepsis condita. Right: Elatocladus gracilis. Images of YPM PB 160858 and YPM PB 160863 by Yale Peabody Museum of Natural History, Division of Paleobotany, Yale Peabody Museum 2015 (CC0 1.0 Universal/Public Domain Dedication, accessed via GBIF.org).

Photograph of a fossil leaves from the Early Cretaceous of Washington. Panel 1: Ginkgo leaf. The leaf is fan-shaped and has dense dichotomizing (forking) veins. Panel 2: Portion of a seed fern leaflet. The leaflet is ovate and has a midvein (central vein) with dichotomizing (forking) veins to either side.

Leaves of seed plants from the Early Cretaceous Winthrop Formation, Washington. Left: Ginkgo leaf (Ginkgo adiantoides). Right: Part of a seed fern leaf (Sagenopteris nilssoniana). Seed ferns are ancient seed-producing plants with fern-like leaves. Images of YPM PB 160843 and YPM PB 160799 by Yale Peabody Museum of Natural History, Division of Paleobotany, Yale Peabody Museum 2015 (CC0 1.0 Universal/Public Domain Dedication, accessed via GBIF.org).

Photograph of a fossil cycadeoid leaf from the Early Cretaceous of Washington. The leaf consists of a central rachis (stalk) with lateral pinnae (leaflets). This specimen is a little more than 3 centimeters long.

Part of a leaf of a cycadeoid (Pterophyllum rectangulari), Early Cretaceous Winthrop Formation, Washington. Cycadeoids are an extinct group of plants that looked somewhat like, but which are unrelated to, palms. Palms are flowering plants, whereas cycadeoids are not. Image of YPM PB 160791 by Yale Peabody Museum of Natural History, Division of Paleobotany, Yale Peabody Museum 2015 (CC0 1.0 Universal/Public Domain Dedication, accessed via GBIF.org).

Cenozoic fossils

Paleogene fossils

Freshwater aquatic animals, trackways, and fossil plants are preserved in Eocene rocks of the Chuckanut Formation and other Eocene formations in northwestern Washington, near the boundary between the Pacific Border and the Cascade-Sierra Mountains regions. These are covered in the Fossils of the Pacific Border.

2-panel image. Panel 1: Black and white photograph of a turtle trackway from the Eocene of Washington. The tracks go from the upper left corner to the lower right corner of a rock slab. Panel 2: Drawing of the same slab shown in panel 1 indicating the positions of the tracks and the distances between them. Distances between left and right tracks are 7.5 to 16 centimeters. Distances between tracks in same line are 15 to 17 centimeters.

A turtle trackway Eocene Chuckanut Formation, Whatcom County, Washington. Left is a photo of the trackway, right is an illustration interpreting the trackway (R = right legs, L = left legs). Source: From Figure 7 in Mustoe (2019) Geosciences 9(7): 321 (Creative Commons Attribution 4.0 International license, image cropped).

Neogene fossils

Most Neogene fossils from the Cascades represent terrestrial forest and grassland communities. Fossil plants include petrified wood from willow, yew, swamp cypresses, and dawn redwoods (Metasequoia).

Fossil vertebrates are less common, but include rabbits, beavers, camels, and the extinct horses Parahippus, Archaeohippus, and Merychippus. 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.

Photograph of a chunk of petrified wood which has been cut and polished on one surface. The grown rings of the wood can be seen has dark lines on the polished surface. The wood is from the Oligocene of Oregon.

Petrified wood (possibly redwood, Sequoia) from the Oligocene of Jackson County, Oregon. Photo by Jessica Utrup, 2016 (Yale Peabody Museum of Natural History/YPM, CC0 1.0 Universal/Public Domain Dedication, accessed via GBIF.org).

Resources

Resources from the Paleontological Research Institution

Digital Atlas of Ancient Life Virtual Collection: https://www.digitalatlasofancientlife.org/vc/ (Virtual fossil collection featuring 3D models of fossil specimens sorted by group)

Digital Encyclopedia of Ancient Life: https://www.digitalatlasofancientlife.org/learn/

Earth@Home: Quick guide to common fossils: https://earthathome.org/quick-faqs/quick-guide-common-fossils/

Go to the full list of resources about fossils in the western U.S.
Go to the full list of general resources about fossils
Back to western U.S. main page
Back to Fossils of the United States main page