When Megalodon Swam Through the Coachella Valley

It’s Shark Week and I think sharks deserve a place on Cactus and Climate, specifically since we talked about how the ocean dictates the weather in the desert. So, today, we are going back in history. 

Roughly 12 to 15 million years ago, two of the earth’s tectonic plates near Baja’s coast stopped grinding one under the other, the way plates still do off the Pacific Northwest today. Instead, they started sliding past each other and pulling apart. That shift tore Baja California away from mainland Mexico and cracked open the rift that became the Gulf of California. Seawater followed the widening rift north into what’s now the Salton Trough, the rift valley running from the Coachella Valley down to the Gulf of California. Two forces keep pulling it apart: the San Andreas Fault system, sliding Southern California northwest toward Alaska, and the East Pacific Rise, an undersea ridge where new ocean floor is constantly forming and pushing the plates apart, the same mechanism that opened the Gulf in the first place. The desert we know today was seafloor.

The Colorado River rewrote that story. Around 5.5 million years ago, two things were happening to the Colorado River at once. Upstream, it was cutting into the Kaibab Plateau, carving out what would become the Grand Canyon. Downstream, it was dumping the resulting sediment into the Salton Trough. Its delta advanced and retreated repeatedly over the next couple million years, alternately choking off and reopening the marine connection, until the sediment finally won. By around three million years ago, the delta had sealed the Salton Trough off from the Gulf for good, and the arm of the sea that once reached toward the Coachella Valley became a freshwater lake, then a dry basin, cycling between the two ever since.

What the Ocean Left Behind

The ocean didn’t pass through quietly. It left rock, and the rock left fossils, and some are still visible today, tucked into a few unmarked corners of the valley and the badlands beyond it.

In parts of the Coachella Valley, oyster beds from the Imperial Formation are exposed at the surface, and mixed in among the shells are shark’s teeth and otoliths, the small ossified ear bones that fish leave behind. Farther out in the desert badlands to the southeast, the same ancient seafloor holds a denser record: sharks, rays, corals, whales, even walrus. In one badlands canyon, a tooth from Otodus megalodon, the largest predatory shark that has ever lived, turned up in the rock, documented in a 2019 peer-reviewed study on the species’ extinction. Elsewhere, a fossil bed of oysters and scallops marks the shoreline where the sea finally shallowed out and gave way to land.

I’m leaving out exact locations here. Fossil sites like these are federally protected, and after years working in conservation, I’ve watched what happens to fragile ground once people know exactly where to stand. 

One of those fossils, the megalodon tooth, belongs to an animal worth a closer look, since the popular image of it gets a surprising amount wrong: how big it was, how fast it swam, and whether it’s really the great white’s ancestor.  

Enter the Giant Megatooth, One of the Largest Sharks to Ever Exist

For decades, the giant megatooth (Otodus megalodon), commonly called megalodon, was classified as a direct relative of the great white shark, under the name Carcharodon megalodon, (megalodon meaning ‘big tooth’). Closer analysis of tooth shape and enamel structure overturned that. Megalodon actually belongs to its own family, Otodontidae, one that split off from the great white’s family tree back in the Early Cretaceous, tens of millions of years before either shark existed in the form we’d recognize. They don’t share a recent ancestor. They share a very old one, and the two lineages went on to evolve separately for tens of millions of years.

The Giant Megatooth and the Great White Face-Off

A typical adult great white today runs about 11 to 16 feet long, or roughly 3 to 5 meters, with females typically the larger sex. The biggest individuals ever reliably measured reach about 20 feet, or 6 meters, and a few disputed reports, based on bite marks left on whale carcasses, suggest free-swimming great whites may occasionally reach 25 feet, close to 8 meters. The giant megatooth dwarfs all of that. The most cited peer-reviewed estimate puts an adult megalodon at 52 to 59 feet, or 16 to 18 meters, making it one of the largest sharks ever to exist. Even at the conservative end of that range, the megalodon was roughly three times longer than the largest great white ever confirmed, and closer to four times the length of a typical adult today.

Researchers at DePaul University, comparing the giant megatooth’s build to living sharks, found it more closely resembled the slender, streamlined body of a modern lemon shark (Negaprion brevirostris) than the bulkier build of a great white. 

Scientists disagree on how fast the giant megatooth actually swam. One study, led by researchers at the Zoological Society of London published in Biology Letters, modeled the swim speeds sharks need just to sustain their own breathing, and concluded megalodon could cruise at over 16 feet per second, roughly 5 meters per second, faster than any shark alive today. A separate 2025 reassessment in Palaeontologia Electronica, working from body reconstructions and scale morphology, arrived at a far slower figure: megalodon cruising at only 2 to 3 feet per second, less than 1 meter per second.

For comparison, a 2019 study that tagged adult white sharks hunting off Australia’s Neptune Islands found they typically cruised between roughly 3 and 4 feet per second, with brief sustained bursts up to about 6.5 feet per second while traveling long distances. Set against that real-world adult baseline, the ZSL estimate would make megalodon roughly four to five times faster than a hunting great white. The 2025 Palaeontologia Electronica study puts megalodon at close to the same pace as that hunting great white, maybe even a bit slower. Two peer-reviewed teams, two very different pictures of the same extinct animal. 

Older Than the Desert Itself

Sharks, and the lineage they belong to, are almost incomprehensibly old. The earliest shark fossils date back roughly 400 million years, long before the first dinosaurs, long before most land plants had even taken root. The giant megatooth lived for more than 15 million years. Fossil evidence puts it on Earth from roughly 20 million years ago until its disappearance around 3.6 million years ago, stretching across the Miocene and Pliocene. A 2019 study reexamined the fossil record and narrowed that 3.6 million year estimate down to 3.51 million years ago.

The ocean that once reached the Coachella Valley was still open water for part of the giant megatooth’s lifetime. By around 3 million years ago, the sea covering this basin had been sealed off by river sediment and reduced to an inland lake, and not long after, dried into the desert we know today. The shark whose tooth was found here was swimming through the Coachella Valley not long before the ocean disappeared for good.

No sharks roam the Coachella Valley today. But their teeth are still out there in the rock, tucked into a few unmarked corners of the valley and the badlands beyond it, proof that this ground has always been shaped by water arriving, leaving, and rearranging everything in between. Reason enough, on Shark Week, to remember that the desert wasn’t always dry.

---

---

Sources:

NASA Earth Observatory, “Salton Trough” — definition and tectonic setting of the Salton Trough. science.nasa.gov/earth/earth-observatory/salton-trough-81711

Dorsey, R.J., O’Connell, B., McDougall, K., and Homan, M.B. “Punctuated Sediment Discharge During Early Pliocene Birth of the Colorado River: Evidence from Regional Stratigraphy, Sedimentology, and Paleontology.” Sedimentary Geology, 2018 http://dx.doi.org/10.1016/j.sedgeo.2017.09.018 

Alles, “Geology of the Salton Trough” — original figures for the 5.5 Ma sediment start date and Grand Canyon carving correlation. Cite this directly rather than the phrasing, since your draft closely mirrors its wording. fire.biol.wwu.edu/alles/GeologySaltonTrough.pdf

EARTH Magazine, “Benchmarks: July 26, 1905” — the Colorado’s delta migrating back and forth between the Gulf and the Salton Trough over the following few million years, and the more recent Lake Cahuilla cycle. earthmagazine.org/article/benchmarks-july-26-1905-rising-salton-sea-swamps-southern-pacific-railroad

UC Riverside Palm Desert Center, California Naturalist Program, “Geology as a form of time travel” — Imperial Formation fossils at Willis Palms/Thousand Palms and near Whitewater Canyon, within the Coachella Valley itself. palmdesert.ucr.edu/calnatblog/2024/01/22/geology-form-time-travel

Boessenecker RW, Ehret DJ, Long DJ, Churchill M, Martin E, Boessenecker SJ. 2019. The Early Pliocene extinction of the mega-toothed shark Otodus megalodon: a view from the eastern North Pacific. PeerJ 7:e6088 https://doi.org/10.7717/peerj.6088 

Shimada, K., Motani, R., Wood, J. J., Sternes, P. C., Tomita, T., Bazzi, M., Collareta, A., Gayford, J. H., Türtscher, J., Jambura, P. L., Kriwet, J., Vullo, R., Long, D. J., Summers, A. P., Maisey, J. G., Underwood, C. J., Ward, D. J., Maisch, H. M., Becker, M. A., & Siversson, M. (2025). Reassessment of the possible size, form, weight, cruising speed, and growth parameters of the extinct megatooth shark, Otodus megalodon (Lamniformes: Otodontidae), and new evolutionary insights into its gigantism, life history strategies, ecology, and extinction. Palaeontologia Electronica, 28(1), a12. https://doi.org/10.26879/1502

Watanabe, Payne, Semmens, Fox, and Huveneers, “Swimming strategies and energetics of endothermic white sharks during foraging,” Journal of Experimental Biology (2019) — adult white shark cruising speeds (modal 0.80–1.35 m/s) and sustained travel speed (2 m/s). doi.org/10.1242/jeb.185603

Natural History Museum (UK), “Shark evolution: a 450 million year timeline” — earliest shark fossil evidence, roughly 400-450 million years old. nhm.ac.uk/discover/shark-evolution-a-450-million-year-timeline.html 

Save Our Seas Foundation, “Megalodon shark” — lifespan range (20 Ma to 3.6 Ma). saveourseas.com/worldofsharks/megalodon

Zoological Society of London, “How fast was the megalodon?” — summary of the Biology Letters cruising-speed study. zsl.org/news-and-events/news/how-fast-was-megalodon

Gabriel Paladino Ibáñez, “Otodus megalodon,” personal naturalist/photography website, June 9, 2024. gabrielpaladino.com/2024/06/09/otodus-megalodon