Traces and remains of ancient creatures—from whale-ribs to a famous mastodon tooth—frequently surface on Santa Cruz beaches and in the Santa Cruz Mountains.
By Kathleen Aston
Mar. 12, 2024—Santa Cruz is renowned for its biodiversity—not just above ground but also below. Watching for winter storms here can be about waiting to see what the wind, rain and waves expose.
On the beaches, fantastical looking skulls emerge from below the sand. In the mountains, clumps of extinct sand dollars and the age-worn edges of shark teeth tumble out of hillsides.
There are few things more magical than finding a fossil in your own backyard, whether it’s your actual yard or your favorite hiking spot. It’s a moment that evokes the triumphant joy of the scavenger hunt, the mind-boggling awareness of the depth of time, and the mysteriousness of even the most familiar places. This is especially true in the Santa Cruz Mountains and the local beaches, where finding a fossil most often means finding remains of ancient oceans on what is now land.
These remains take two main forms: body fossils and trace fossils. Body fossils include the preserved remains of organisms. A shark tooth, a whale rib whose organic tissues have been replaced with inorganic minerals, or stones shaped by the curved interior of an ancient snail shell are all body fossils. Trace fossils are the indirect evidence of an organism’s existence. Locally that often means fossilized burrows of marine invertebrates, but can also include things like footprints and, famously, fossilized feces AKA coprolites.
Hard bits, like teeth and bone, are much more likely to be found as fossils. Creatures who died in the presence of water, and who were buried quickly, are also much more likely to undergo the type of preservation that lasts for millions of years. In the present, there is often no hard and fast rule to tell whether what you’ve encountered is a fossil or a bone, but fossils are likely to be heavier and darker. Meanwhile, determining whether what you’ve found is bone or stone can be tricky too—oftentimes you’re looking for a sort of spongy texture that indicates the specimen has the structure of a once-living bone.
Where to Find Fossils in Santa Cruz
Ultimately, much of knowing what you’re looking at is also about where you’re looking. Geologic context can tell us a lot about fossils, which is part of why it is so important to have a good understanding of where you are when you find one.
Scientists study the ground below our feet in units called formations, each of which have a particular set of characteristics. In Santa Cruz, which has a lot going on geologically, there are three formations where you are most likely to find fossils in your average wanderings.
The Purisima Formation in Santa Cruz is a sandstone formation deposited approximately 3-7 million years ago under shallow, near-shore conditions. Distinguished by its blue-gray hue, this formation features a coarser composition compared to the Santa Cruz Mudstone that succeeded it.
Rich in fossils, particularly invertebrates such as mollusks, as well as cetaceans and pinnipeds (whales and seals), the Purisima Formation stretches from Merced Avenue intersecting West Cliff Drive in Santa Cruz down to the cliffs of Seacliff State Beach.
The older Santa Cruz Mudstone Formation, formed between 7-9 million years ago, represents a geological era when the sediment settled in deeper waters, resulting in finer silt and clay deposits. This distinct formation, characterized by its yellow tone and rusty red cracks caused by methane seepage, overlays parts of the Purisima Formation.
While it’s challenging to find fossils in the Purisima Formation compared to its predecessor, the Santa Cruz Mudstone formation occasionally yields small bivalves such as clams, echinoids including sand dollars, and even notable discoveries such as teeth from the iconic O. megalodon. Dive deeper into this formation with a blog exploring the layers at the Swift Street outcrop.
Digging Deep Into the Distant Past—and Sharing What We Find
The Santa Margarita Formation in Santa Cruz, dating back to 10-12 million years ago, is a marine deposit of Miocene sandstone and conglomerate. Recognizable by its rough, chunky, and sparkling white appearance, this formation holds a treasure trove of fossils, including sharks, rays, sea cows, sea lions, and various invertebrates.
Most well known for its accessibility at old quarry locations in the Santa Cruz Mountains, the Santa Margarita Formation contributes significantly to the region's rich paleontological heritage, with some of its remarkable finds showcased in exhibits at your local natural history museum. See more of these fossils, this formation, and local fossil hunters in this webinar.
Of course, finding fossils isn’t the final part of the story—oftentimes they are also collected. In the best of these cases, when they are collected responsibly, they are then shared through science and public education. You can check out this guide on our website to help you determine when to take home a treasure and when to take its photo and send it to a museum or scientist.
As a small regional museum, we have to be picky about what we collect. Specimens must fit in our storage space, fill gaps in our inventories, and present features that paleontologists tell us can expand existing scientific understanding. A huge part of their scientific viability depends on whether they have associated data—even if they were a beloved keepsake from a family member, if they don’t have information about where and how they were collected, they can’t add a lot to the scientific story.
Regardless, by letting us know when you find something, we are able to document the discovery and pursue collecting it ourselves or connecting it with the scientific community. That way, our museum can continue to support public understanding of the history of life in the Monterey Bay region, and we can all continue to see into the wondrous world of the remote past in the adventures of our present.
Dig into the fascinating world of fossils during this month’s Family Fun with Fossils day at the Museum on March, 30, 2024, and view the events calendar for more ways to explore nature in Santa Cruz.
Kathleen Aston is Collections Manager at the Santa Cruz Museum of Natural History.
Read about a new fossil discovery! "Fossil Sloth Bone Found in the Santa Cruz Mountains, the First of Its Kind Report in This County"
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