You’ve surely seen those dramatic museum displays: fearsome T-Rex skulls, triceratops horns, towering brachiosaur skeletons – tangible reminders of a world with giant animals that roamed our planet millions of years ago. Some states are rich in the fossils of ancient dinosaurs. Montana, Wyoming, Utah all have rich fossil records. But not California. Very few dinosaur fossils have ever been found in the Golden State.

But why? We’ve got Hollywood, Silicon Valley, lots of oil, and the Giant Redwoods, but where are our prehistoric dinosaur residents hiding?

To understand this prehistoric puzzle, we have to venture back into the geologic past, and also consider some unique aspects of California’s geographical and geologic evolution.

A Journey Through Geologic Time

Dinosaurs were most prolific during the Mesozoic Era, from about 252 million to 66 million years ago (it ended with a massive meteorite impact that caused a mass extinction, wiping out the dinosaurs and up to 80% of life on Earth). The Mesozoic is divided into three periods: the Triassic, Jurassic, and Cretaceous. While dinosaur fossils are found around the globe, their distribution is far from even. Fossilization itself is a relatively rare event that depends on a number of specific conditions. Generally, fossilization requires rapid burial to protect the remains from scavengers and environmental factors, as well as a lack of oxygen to slow down decay. Over time, minerals gradually replace organic material, preserving the structure and creating a fossil, but only a small fraction of organisms ever undergo this process.

Thus, when a dinosaur died, its body needed to be quickly covered by sediment, like sand, mud, or volcanic ash. This prevented the remains from being scavenged or decomposed and allowed for the slow process of mineralization, where bones and teeth gradually turn to stone.

Even if these conditions were met, the resulting fossils had to survive millions of years of geologic processes, such as erosion, plate tectonics, and volcanic activity. To find dinosaur fossils today, the layers of rock in which they are embedded must be exposed at the Earth’s surface.

California’s Geologic Past

Here’s where California’s unique geologic history comes into play. Most of the land we see today in California wasn’t even above sea level during the Mesozoic Era. Instead, it was under the Pacific Ocean. Some regions that were above water, like parts of Southern California and the Central Valley, were often the sites of volcanic activity or were being reshaped by the movement of tectonic plates.

While these environments were not ideal for the preservation of dinosaur fossils, they did produce the rich fossil marine record found in the state, including ammonites, marine reptiles, and microfossils. And the tectonic activity that was so detrimental to dinosaur fossil preservation is responsible for the formation of the gold that sparked the state’s famous Gold Rush. In other words, California is relatively new land that rose out of the ocean at the end of the dinosaur age.

That said, there have been several discoveries of particular animals in California. The majority of the dinosaur fossils found in California are the bones of hadrosaurs, duck-billed dinosaurs that lived during the Late Cretaceous period. These herbivorous dinosaurs thrived in what was once a coastal plain environment, and their remains have been uncovered primarily in areas that were once submerged by ancient seas, such as parts of the San Diego Formation.

The ocean side of California was home to the Mosasaurs – large, carnivorous marine reptiles that lived during the late Cretaceous in oceans all over the world. They had fins on their long bodies, and sharp teeth in their long jaws. They ate fish, ammonites, and possibly even other mosasaurs. Lucky for us, mosasaurs are now extinct — they died out with the dinosaurs at the end of the Cretaceous. They grew to enormous sizes and ruled the seas at the time. They existed near the closing of the Cretaceous period, sharing the earth with the likes of Triceratops and Tyrannosaurus. A unique combination of knobs and muscle attachment scars, a distinctive feature on their skeletal framework, aids in their identification.

Back to hadrosaurs more specifically, there is the duck-billed plant-eater Augustynolophus, a member of the hadrosaur family, which recently was named the official state dinosaur of California. Only two specimens of A. morrisi have ever been found, both of them in California. The first fossil of the ancient beast was uncovered in Fresno County in 1939. The second was discovered nearby in 1941 in San Benito County, according to the Natural History Museum of Los Angeles County website. Named after paleontologist William J. Morris and NHMLA patron Gretchen Augustyn, Augustynolophus morrisi is one of few dinosaurs that have been discovered in the state.

 

The action of plate tectonics, the slow but powerful movements of sections of the Earth’s crust, has also significantly affected California’s fossil record. Over millions of years, California has been built from pieces of the Earth’s crust that traveled here aboard tectonic plates.

Much of the rock we see at the surface today, especially along the coast and in the western mountains, arrived during the Cenozoic Era, after the age of dinosaurs. These younger rocks, while not bearing dinosaur fossils, have yielded rich caches of mammal fossils, including creatures like saber-toothed cats, mammoths, and dire wolves, which roamed California long after the dinosaurs.

In recent years, paleontologists have begun to find more dinosaur fossils in California, albeit still far fewer than in states like Utah, Montana, or Wyoming. These discoveries, often of marine animals or those who lived near the coast, are expanding our understanding the ancient Californian landscape.

In 2022, a remarkable fossil discovery was made during a construction project at San Pedro High School in Los Angeles. The excavation revealed a massive trove of marine fossils from the Miocene Epoch, dating back around 5 to 23 million years. Among the finds were the remains of ancient whales, sharks, fish, and mollusks, offering a rare glimpse into Southern California’s prehistoric past when the region was submerged under a warm, shallow sea. This discovery provided paleontologists with valuable insights into the marine ecosystems that once thrived in the area.

In addition to marine fossils, some terrestrial remains were found, suggesting a coastal environment that hosted a range of species. The well-preserved fossils captured the attention of both scientists and the local community, turning the high school campus into an unexpected scientific hotspot. For the students and residents of San Pedro, the find underscored the fascinating ancient history hidden beneath their feet.

All said, while we may not have an abundance of dinosaur fossils in California, the state’s unique geologic past and diverse environments have produced an incredible variety of other ancient life. From the towering sequoias to the microscopic plankton, every fossil tells a part of California’s rich, complicated, and constantly evolving story.