Mojave National Preserve, in California's Mojave Desert, holds rocks from the Paleoproterozoic — 2.5 to 1.7 billion years ago — to the present. Its mountain ranges expose that record between wide valleys, dunes, cinder cones and a low, seasonal salt lake. Its fossils run from at least about 550 million years ago, late in the Proterozoic, to the Holocene, which began 11,700 years ago:
| Age | Fossils |
|---|---|
| Late Proterozoic through most of the Cambrian | abundant, varied marine life |
| Devonian through early Permian | more marine fossils |
| Cenozoic | plants and animals in volcanic tuff and valley sediments |
To understand and protect them, NPS staff produced a paleontological resource inventory. From October 2021 to January 2022, they field-checked 13 fossil localities — known sites, and new ones found through the literature and tips from park staff.
A rare window on early animals
Geologist John Hazzard was the first to study the preserve's fossils seriously, identifying Paleozoic assemblages in the Kelso and Providence Mountains in the 1930s and 1940s. For the inventory, physical scientist Sofia Andeskie and Scientist-in-Parks intern Emily Johnson measured a detailed section of the Proterozoic-to-Cambrian rocks in the Kelso Mountains. From oldest to youngest:
| Formation | Rock | Fossils |
|---|---|---|
| Wood Canyon Formation | middle member: yellow to orange-brown sandstone; upper member: about 20 m (66 ft) of mudstone and sandstone | spans the Proterozoic–Cambrian boundary and the early spread of animals with hard parts; the team saw vertical burrows about 1 cm across; others have reported horizontal and "soda-straw" burrows (Skolithos), the frond-like Swartpuntia, sponges and trilobites |
| Zabriskie Quartzite | 20 m (66 ft) of white to yellow, fine sandstone | none seen; Skolithos reported |
| Latham Shale | dark gray, brown and greenish-gray mudstone | cyanobacteria, a possible jellyfish-like cnidarian (Sphenothallus?), brachiopods, hyoliths, an undescribed armored worm, radiodonts like Anomalocaris, olenellid trilobites, eocrinoids and traces |
| Chambless Limestone | hard, ridge-forming gray limestone with dark "algal" nodules stretched by tectonic stress | brachiopods, hyoliths, snails, trilobites, eocrinoids |
The head of an olenellid trilobite in a slab of Latham Shale. NPS photo by Justin Tweet
These rocks give the preserve some of the most unusual Cambrian fossils in the national park system:
- the system's only radiodont, its only armored worm, and its only late-surviving Ediacaran organism (Swartpuntia)
- one of three park records of eocrinoids, and one of two of the puzzling Sphenothallus
- one of the few rock sections in the parks that cross the Proterozoic–Cambrian boundary
Mississippian seafloor: the Monte Cristo Formation
The Monte Cristo Formation, of early to middle Mississippian age, is mostly light and dark gray limestone laid down in a shallow sea, in four or five members. In several places in and just outside the preserve it is packed with fossils: corals, sponges, bryozoans, brachiopods, bivalves, ammonoids, nautiloids, snails, trilobites, ostracodes, crinoids and possibly sea urchins.
Sponges in crinoidal limestone, Providence Mountains. NPS photo by Emily Johnson
Coral in the Monte Cristo Formation, Providence Mountains. NPS photo
Miocene lakes and mammals
Hobby collectors found the first reported vertebrate fossils, in the Hackberry Wash area, in the 1960s. In the 1970s and 1980s, workers from the San Bernardino County Museum explored Hackberry Wash and Wild Horse Mesa, in lake deposits laid down near volcanoes — rocks sometimes called the informal Winkler Formation — and defined two local faunas:
| Local fauna | Setting | Fossils |
|---|---|---|
| Wild Horse Mesa | between the Peach Springs Tuff and the Wild Horse Mesa Tuff | logs and wood of Sequoia langsdorfii, other conifer wood and needles, grasses and reed-like plants, ostracodes, and flamingo tracks |
| Hackberry Wash | with the Wild Horse Mesa Tuff, in silicified shale with jasper | a rodent, a pika, a dog, a cat, a rhino, camels and a small deer-like artiodactyl |
Reed-like fossils in the Wild Horse Mesa Tuff, seen by park staff near the Hackberry Wash digs. NPS photo by Sofia Andeskie
Why it matters
The inventory report sets a baseline for the preserve's fossil record — its scope, significance and distribution — and a foundation for protecting it and for future education, interpretation and research.
Sources
Based on Sofia Andeskie, Emily Johnson, Justin Tweet, Vincent L. Santucci and Debra Hughson, "Mojave National Preserve Paleontological Resource Inventory," Park Paleontology News, Fall 2023, National Park Service, summarizing Johnson and others, Mojave National Preserve: Paleontological Resource Inventory (2023); a work of the United States government in the public domain; rewritten in hubnx's own words.
In these publicationsMojave National Preserve
Licence: CC0 1.0 (public domain) · Adapted from www.nps.gov
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