Way back in the Pleistocene epoch, a group of 20,000-pound, 14-foot-high Columbian mammoths — essentially gargantuan elephant cousins — raised their enormous trunks into the breeze on what is now coastal California and caught a whiff of delicious grass. It was coming from Santarosae, a mountain island abundant with vegetation. So the mammoths made use of their top-notch swimming skills, built-in snorkels and buoyant bulk, and crossed the channel.
Back when they did this, the sea level was some 300 feet lower than it is today, which meant the swim was only about 6 miles. They may well have gone back and forth, but eventually a bunch of ice sheets and glaciers melted and the sea level rose, shrinking and separating Santarosae into what is now the four northernmost Channel Islands — and stranding the mammoths. By the time that happened, a lot more mammoths had shown up on the islands and chowed down.
When the food supply became more limited, mammoths that needed less food to survive suddenly had an advantage. As in, smaller was better. And because the mammoths had no natural predators, large size was no longer needed for defense. After some 20,000 years under these conditions, mammoths shrunk down to 5 or 6 feet tall.
Half the size of their ancestors, they were pygmies, an entirely new species. Alas, they were doomed from the start.
About 10,000 years ago, pygmy mammoths and lots of other megafauna went extinct for reasons that people can’t agree on. Some say it was global warming at the end of the last Ice Age, others say pygmy mammoths were hunted out of existence by the Chumash people, and still others think it was a combo. Regardless, all we have left are their undersized bones. Here’s some better news, though: The island I was visiting that day — Santa Rosa — is the one where the most mammoth fossils have been unearthed.
To learn more, I talked with park ranger David Begun, who was just starting out as a volunteer at the park back in 1994, the same year that the world’s only complete pygmy mammoth skeleton was discovered on Santa Rosa Island.
“Nothing like that had ever been found,” Begun said of the perfectly preserved, pony-sized skeleton dating back about 12,800 years. “That was exciting.”
According to Begun, most of the mammoth fossils from the Channel Islands have been unearthed on Santa Rosa. The mammoths roamed all of the northern islands, Begun says, but Anacapa and Santa Cruz are mostly volcanic rather than sedimentary. To the west, the sandier composition of San Miguel and Santa Rosa allowed for mammoth skeletons to be buried and fossilized.