Fossil Walruses and Other Ancient Life in the Monterey Bay with Dr. Robert Boessenecker

Though our coast today is inhabited by sea lions, harbor seals, and elephant seals, none of these species existed in California 3-5 million years ago. Instead, fossils from the Purisima Formation tell a very different story of strange walruses and early fur seals that inhabited our coast. These include the ancestor of the modern northern fur seal (today a rare visitor to Monterey Bay), the bizarre “double tusked” walrus Gomphotaria, and the toothless walrus Valenictus. Several discoveries made by local collectors and paleontologists represent new species — and you’re going to hear new data and findings never reported before during this presentation.

Join us on National Fossil Day for this member-exclusive presentation with longtime friend of the Museum, Dr. Robert Boessenecker.

Dr. Robert Boessenecker

“I grew up in Foster City on the peninsula, disappointed as a dinosaur nerd kid that there weren’t much in the way of dino fossils from California – which I mistook for “no interesting fossils at all”. Once in high school I visited some shark tooth sites in Scott’s Valley and became obsessed with marine mammal fossils none of the fossil collectors could identify. As an undergraduate student at Montana State University, I started collecting and researching a marine mammal fauna I discovered in Half Moon Bay; I continued with my master’s thesis at MSU on the preservation and stratigraphic context of Purisima Formation fossils, and then went to University of Otago in New Zealand to do my Ph.D. on early baleen whales from much older rocks down under. I have been at the College of Charleston in South Carolina, studying early baleen whales and dolphins, and once again researching Purisima Formation sharks, fish, birds, turtles, and marine mammals.”

-Dr. Robert Boessenecker

About the series

Zoom into the stories, secrets, and science of our collections during monthly webinars with Collections Manager Kathleen Aston. This live event is an extension of our monthly Collections Close-Up blog, with added insights and intrigue. Members are invited to participate in this program before it is made available to the general public as well as ask questions directly of Kathleen.

Not yet a Member? Join today!

Your support helps us steward our collections and offer educational programs that connect people with nature and science. Memberships start at just $15/year.

Rock Record: Panther Beach, an Extraordinary Geologic Feature in Santa Cruz

Written by Gavin Piccione

One of the most exciting perks of having an appreciation for geology is the limitless possibility to find new geologic features, even on the most seemingly mundane trips outside. It may be an interesting pebble that catches your eye or a new outcrop that piques your interest, but one usually does not have to travel far to find thought-provoking rocks. However, within this vast collection of terrestrial curiosities, some features stand out as particularly exceptional or interesting.

On a recent trip to Panther Beach, I experienced the thrill of discovering one of these remarkable geologic marvels hiding just up the coast. In this installation of Rock Record, I cover why the rocks at Panther Beach in Santa Cruz are a world-renowned sedimentary outcrop, and I investigate how this truly unique part of the cliff was deposited here.

The Rocks at Panther Beach

At first glance the rocks at Panther beach may look very familiar to folks who have spent time in Santa Cruz, with cliff walls of the main section of beach made up of the crumbly, beige sedimentary rock called Santa Cruz mudstone. However, if you head to the south-end of the beach, and pass under the archway, the rocks change drastically. Instead of the highly uniform mudstone, the rocks on this side are wavy, laminated sandstones (see image 1). Below these peculiar sandstones there are darker rocks, called dolomite-cemented sands, that have bands that tilt down and towards the southeast. If one breaks or scratches these dolomite-cemented sands, they may smell the faint odor of petroleum. The contact between these two rock types is high irregular, looking almost as if the dolomite-cemented sands were bubbled up into the wavy sandstones like liquid in a lava lamp (see images 2 and 3). Capping these two sandstones is the familiar Santa Cruz mudstone that makes up the rest of the cliff (see full outcrop in image 4).

Image 1: Wavy sandstone at Panther Beach
Image 2: Contact between the wavy sandstone, and the dolomite-cemented sandstone. Image from Sherry, et al. 2012
Image 3: Contact between the wavy sandstone, and the dolomite-cemented sandstone. Image from Sherry, et al. 2012
Image 4: Panther Beach outcrop. Image modified from Sherry et al. 2012

Formation of the Panther Beach Outcrop: The World’s Largest Sedimentary Injection Deposit

When geologists see large sections of rock that are unrelated to the surrounding rock, we often think of some surface process like motion along a fault, that may bring two different rock types in contact. However, at Panther Beach there is no evidence for a fault that could have brought the sandstones to the surface. So how did this ~100m section of sandstone become emplaced in a cliff that is otherwise made of Santa Cruz mudstone?

To understand the formation of the Panther beach outcrop we must start about 1 kilometer below the seafloor. Around 9 million years ago off the coast of ancient Santa Cruz, 1000 meters of mud (the Santa Cruz mudstone) was deposited at the bottom of the ocean above a thick sand deposit (the Santa Margarita sandstone). Later, after heat, and pressure turned most of these sediments into rock, the only sediments left were small pockets of Santa Margarita sands that had not been lithified (i.e., turned to rock). Portions of these sand pockets were rich in oil, which created two distinct reservoirs: oil-rich sands and oil-poor sands. These two sand types were spatially separated because of the density difference between oil and water (see image 5).

Image 5: Sediments prior to injection. Schematic modified from Sherry, et al. 2012.

As more mud was deposited atop the Santa Margarita Sands, the pressure on the sand built. Then finally a geologic event, probably either an earthquake or a landslide, shook the sediments causing the slurry of both oil-rich and oil-poor sands to be injected, at a high velocity, into the overlying rock through fractures in the Santa Cruz mudstone. This type of formation is called a sediment injection deposit, where sediments from below are squeezed up into the overlying strata like a tube of toothpaste (see image 6). While the sands were injected, the oil-rich sand slurry would have traveled slower than the oil-poor sands, leaving the oil rich sands below the oil-poor sands. Injection deposits occur in other places on Earth, but the Panther Beach outcrop is the largest sedimentary injection deposit in the world!

Image 6: Sediments after injection. Schematic modified from Sherry, et al. 2012.

Getting to the Panther Beach Outcrop

Image 7: View looking towards the south through the archway in the cliff

Panther Beach is located off Highway 1 about 5 miles north of Santa Cruz. The parking lot for beach access is unmarked but can be found on google maps. The walk to the beach is about 50 yards down a narrow, steep trail (see the image at the start of this post for the view from the top of the trail). Once on the beach, turn left and walk under the arch in the cliff (see image 7). Be careful, this passageway may not be accessible at high tide, use caution when walking through and do not try to pass when water is high! The sedimentary injection deposit makes up the sea cliff beyond the south side of the arch.

The GPS coordinates for Panther Beach are: 36.994, -122.169

Much of the information for this edition of Rock Record was first published in the journal article: Emplacement and dewatering of the world’s largest exposed sand injectite complex, by Timothy Sherry and others.

Reference cited:

Sherry, T. J., Rowe, C. D., Kirkpatrick, J. D. & Brodsky, E. E. Emplacement and dewatering of the world’s largest exposed sand injectite complex. Geochemistry, Geophys. Geosystems 13, 1–17 (2012).

A Guide to the Rocks of Santa Cruz County

Santa Cruz is an area of geologic interest with a complex history of processes that shaped the coastline, bluffs, terraces, and mountains we see today! Wind, waves, earthquakes, fires, and other natural forces have changed and shaped the landscape for millions of years, though humans have only been able to document those changes in the recent past.

Jump To: Formations | Rock Types | Minerals | Resources

Geologic Formations

The above map shows the distribution of different rocks in Santa Cruz County. Each color represents a different kind of rock and, in turn, a particular age. Many of these rocks represent formations.

A geological formation is a basic rock unit that geologists use to group rock layers. Each formation must be distinct enough for geologists to tell it apart from surrounding layers and identify it on a map. A formation can consist of a variety of related or layered rocks, rather than a single rock type. There are over 14 geologic formations in Santa Cruz County. Most of these formations were created through movement of the crust because of tectonic uplift at the subduction zone off the California coast.

Most of the county is underlain by granitic rock. It formed about 100 million years ago from molten rock which cooled very slowly at a depth several miles below the earth’s surface. Since then, this area has been covered by the sea much of the time. Sand, mud and other sediment was deposited on the seafloor and was eventually compressed and hardened into sedimentary rock which was uplifted to form the Santa Cruz Mountains. Many of the sedimentary beds, which were originally horizontal, have been tilted, folded or partly eroded away. In some areas major faults have offset the rocks.

A large fossil in grey rock on the beach.

3 formations are known for fossils in this region:
Purisima Formation (3-7 Ma)
Santa Cruz Mudstone (7-9 Ma)
Santa Margarita Formation (10-12 Ma)

Learn more in our Fossil Guide.

Rock Types of Santa Cruz County

The three basic types of rocks- igneous, metamorphic and sedimentary– occur in Santa Cruz County. All are composed of minerals. Some consist of primarily one mineral, as in the case of marble, while others are an aggregate of many different minerals, as in the case of granite and conglomerate. 

Each rock type in the Santa Cruz area represents a different chapter in this region’s geologic past, and each has its own unique story to tell. The rocks of this area are mostly covered by soil and vegetation, so geologists must rely on scattered outcrops in creek beds, quarries, road cuts and sea cliffs in order to piece together the geologic history. 

Granite, Empire Grade Road

Igneous rocks formed from molten rock called magma. Plutonic rocks, such as granite, gabbro and alaskite, cooled very slowly, solidifying deep below the earth’s surface. This provided time for larger crystals of quartz, feldspar, mica and other minerals to form, giving the rocks a coarse texture. Volcanic rocks, such as basalt, cooled quickly at the earth’s surface and are very fine grained.

Marble, UCSC Quarry

The metamorphic rocks of this area are a geological enigma. They predate the granite rocks and were originally sedimentary rocks such as limestone, shale and sandstone. These were respectively metamorphosed into marble, schist and quartzite by the intrusion of magma about 100 million years ago. How much earlier these rocks were laid down as sediment, however, remains a mystery.

Mudstone, HWY 1 North of Santa Cruz

Sedimentary rocks in the Santa Cruz area originated for the most part from sediment such as mud, sand and gravel that was deposited on the sea floor. Over millions of years chemical alteration and pressure from burial hardened the sediment into rock. These rocks overlie the igneous and metamorphic rocks of this region and are of a younger age. 


Minerals are the naturally occurring crystalline substances that make up the rocks around us. Minerals such as quartz, feldspar, and calcite are the most common constituents of rocks in this area. Dozens of other mineral species occur here, but in small amounts. Large, well-formed crystals- the kind most sought after by collectors- are scarce. 

Several minerals in this region have proven to be of great economic importance. Cinnabar (the chief ore of mercury) has been mined extensively at the New Almaden on the east slope of the Santa Cruz Mountains. Calcite (in the form of marble) has long been quarried near Santa Cruz for the manufacturing of lime and cement. 

Benitoite is the California state mineral. This unusual blue crystal was first discovered in 1907 in San Benito County. While benitoite is found in a few places around the world, San Benito County is the only place in the world where gem quality benitoite crystals are found.

Learn more in our Collections Close-Up.


Explore other resources for better understanding geology, paleontology, and the landscape of the Santa Cruz region.

Geology at the Museum

On exhibit at the Museum

  • Specimens of common minerals from the region
  • Specimens of common rocks from the region
  • A detailed topographic geologic map of the county
  • Garden: Take a stroll around the Museum’s Garden Learning Center and see if you can spot fossils and other large rock samples.
  • Activities for kids: Multiple dig boxes features Santa Margarita Formation fossils of sand dollars and casts of a fossil sea cow.

Bring rocks home

Rent a kit to explore local rocks at home. Kit rentals are $10 per week and can be requested here (you do not need to be a teacher to request a rental).

Explore Online Rock Resources

Shop the geology and paleontology section of our online store

Books and Papers

Santa Cruz Top 5 Geologic Must-Sees

Santa Cruz is an area of geologic interest with a complex history of processes that shaped the coastline, bluffs, terraces, and mountains we see today! Use this map as you walk, bike or ride your way across the county and explore some of the geologic must-sees our area has to offer. Visit our online Guide to the Rocks of Santa Cruz County to dig even deeper into the geology of the region.

On the Rocks: The Paleontologist’s Paradise

A layered cocktail in a highball glass

This month join us in raising a glass to the field of paleontology (the study of fossils) as we explore geologic time through a layered drink in one of our favorite glasses.

The history of life on earth is measured in millions of years, and humans are only a tiny blip in that long history. While geologic time can be a hard concept to wrap your mind around, people like Aristotle (384–322 BCE) first noticed the presence of fossil shells on land and concluded that the shape of the earth’s surface must have changed over time. Early scholars from across the world also made observations about the layering of rocks, and in 1669 the Danish scholar Steno proposed the Law of Superposition, a key concept to the earth sciences which generally states that stratigraphic layers on the bottom of a sequence will be older than those layered on top of them.

These concepts were the building blocks for the geologic time scale as we know it today. The geologic time scale is broken down into four large eons and each eon is then further broken down into eras, which are in turn divided into periods, epochs and ages. Today, we are living in the Holocene Epoch, going back 11,700 years ago it generally marks the end of the last ice age. The Holocene is also referred to as the Anthropogene, the “Age of Man” as of all recorded human history falls in this time period and it acknowledges the huge impact we have had on the earth.

Explore more about geologic time with videos from our Geology Gents and peruse our Guide to Local Fossil if you want to dig even deeper.

Layered drinks such as this one are both eye-catching and a fun way to experiment with the density of liquids. The force of buoyancy keeps the various layers from mixing as long as you are using liquids with different densities and build your drink with the heavier liquids at the bottom. Explore this resource for the relative densities of various liqueurs for your future cocktail creations.


0.5 oz. Grenadine or other syrup of your choice
1.5 oz. Coconut rum
1 oz. Dark rum
0.5 c. Juice (pineapple or other tropical flavor)


  1. Pour the grenadine into the bottom of your glass.
  2. Fill the glass to the top with ice, trying not to splash the grenadine.
  3. Mix your juice with the coconut rum. Slowly pour over the ice so that the force doesn’t cause it to mix with the grenadine.
  4. Top with carefully poured dark rum.
  5. Garnish with the citrus of your choice.


  1. Substitute the dark rum for blue curacao for a more eye-catching color combination.
  2. For a non-alcoholic option, leave out the rum and experiment with the density of other additives like soda water or coconut cream.

Post by Liz Broughton

Rockin’ Pop-Up: What even IS North America?

Santa Cruz County is obviously a part of North America. Right?

Well, it’s a little more complicated than that. There’s the continent of North America, but there’s also the North American tectonic plate — where Santa Cruz County does not reside! While our neighbors in Los Gatos on the other side of the Santa Cruz Mountains are located on the North American Plate, Santa Cruz is located on the Pacific Plate.

There are lots of little (and really big!) geologic surprises across the continent. Join the Geology Gents for this North American road trip!

About the Series: Join the Geology Gents, Gavin and Graham, for monthly conversations about rocks live on Facebook. Each month we’ll explore a different geologic topic, from Santa Cruz formations to tips for being a more effective rockhound. Graham Edwards and Gavin Piccione are PhD candidates in geochronology with the Department of Earth and Planetary Sciences at UC Santa Cruz.

Submit your questions ahead of time by emailing events@santacruzmuseum.org and feel free to include pictures of rocks you’d like identified! Note: you do not need to have a Facebook account to be able to watch the program live.

Watch Past Pop-Ups
Read our blog Rock Record


Resources for Recovery, Preparedness, and Ecological Understanding from the Santa Cruz Museum of Natural History and Santa Cruz Public Libraries

August 2021

See more CZU AND YOU events

A Striking August: Lightning and Wildfires with Chris Giesige

Lightning flashes through purple clouds over the horizon glowing orange.

In August 2020, Northern California was ignited by a series of 650 wildfires spurred by dry lightning from rare, massive summer thunderstorms. Today, all of California is experiencing drought conditions and fire season is well underway.

On the one year anniversary of the lightning storms wildfire researcher and lightning scientist Chris Giesige presented on the weather and climate conditions that made the August 2020 lightning events possible and shared a peek at what the future may hold for wildfires in California. Explore how we classify the weather and atmospheric conditions that create fire weather and behavior, why those conditions aided the events of last August, and explore wildfire in California more generally.


About the Speaker

Chris Giesige has studied fire science and conducted lightning research for over a decade. His research is focused on wildfires and seasonal and short term lightning development during the summer through fall months. Through the WestCats Group, he and his team are currently working on developing a new sensor network for better lightning forecasting for wildfire events.

This program is part of the series CZU AND YOU: Resources for Recovery, Preparedness, and Ecological Understanding from the Santa Cruz Museum of Natural History and Santa Cruz Public Libraries | August 2021

Collections Close-Up: Preserving Cultural History After Fire with California State Parks

Many had to evacuate the Santa Cruz Mountains during the CZU Lightning Complex fires of August, 2020, including museums, visitor centers, and cultural heritage sites managed by California State Parks. Jenny Daly, museum curator for the Santa Cruz District of California State Parks, was part of a team that worked quickly to save artifacts from threatened State Parks, including Big Basin, Año Nuevo, and Wilder Ranch.

During this online event, learn about the immediate steps taken by State Parks to save our cultural history and the ongoing process of caring for objects impacted by the fires. Kathleen Aston, Collections Manager at the Santa Cruz Museum of Natural History, will also share how the Museum approaches natural disasters and collections, from Loma Prieta to ongoing efforts with the CZU Lightning Complex.

Photo of Mark Hylkema by Aric Crabb/Bay Area News Group.

About the Speaker

Jenny Daly, Museum Curator I for the California State Parks in the Santa Cruz District, grew up in Santa Cruz and is fortunate to live and work in her hometown. After transferring to UC Berkeley from Cabrillo College, Jenny received a double BA in Near Eastern Studies and Theater, Performance, and Dance Studies. The most valuable part of her time at Berkeley was the internship she had working with the Registrar at the Phoebe Hearst Museum of Anthropology where she became hooked on the idea of a career working in museums. Jenny then received a Master’s in Museum Studies from John F. Kennedy University and has worked in collections management at various institutions since then, including at the California Academy of Sciences, the Cantor Arts Center, and the Getty Center. Jenny was very excited to start working for the State Parks as a curator because it meant she could combine her love of Parks with her expertise in museum collections management.

This program is part of the Museum’s Member exclusive Collections Close-Up series and our August series in partnership with Santa Cruz Public Libraries, CZU AND YOU: Resources for Recovery, Preparedness, and Ecological Understanding.

Rockin’ Pop-Up: Great Geologic Goodbyes

Graham Edwards and Gavin Piccione with fossil

For over three years, the Geology Gents have been regular fixtures at the Museum — both online and in-person. For this month’s pop-up though, we say goodbye to Graham as he heads out to New Hampshire for his post-doctoral work at Dartmouth College. The good news is that he’ll remain a Geology Gent from afar and Rockin’ Pop-Ups will continue!

In honor of this milestone, Graham and Gavin will be exploring some “great geologic goodbyes” for this month’s pop-up — from extinction events to the dismantling of Pangea.

About the Series: Join the Geology Gents, Gavin and Graham, for monthly conversations about rocks live on Facebook. Each month we’ll explore a different geologic topic, from Santa Cruz formations to tips for being a more effective rockhound. Graham Edwards and Gavin Piccione are PhD candidates in geochronology with the Department of Earth and Planetary Sciences at UC Santa Cruz.

Submit your questions ahead of time by emailing events@santacruzmuseum.org and feel free to include pictures of rocks you’d like identified! Note: you do not need to have a Facebook account to be able to watch the program live.

Watch Past Pop-Ups
Read our blog Rock Record