Santarosae, the Lost Ice Age Island Off California, Had Pygmy Mammoths and Some of America’s First People
During the Ice Age, four of the Channel Islands were one big island called Santarosae, home to pygmy mammoths and some of the earliest people in the Americas. Rising seas drowned most of it.
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Picture a big island off Santa Barbara, covered in forest, with mammoths the size of horses wandering around and some of the first people in the Americas hunting along its shores. It was real. It’s called Santarosae, and it’s gone now, mostly underwater. What’s left of it are four of today’s Channel Islands.
During the last Ice Age, about 20,000 to 25,000 years ago, so much water was locked up in glaciers that sea level was hundreds of feet lower than today. The northern Channel Islands were all one big island. Then, as the cold Pleistocene gave way to the warmer Holocene, the epoch we live in now, the ice melted, the oceans warmed and expanded, and the sea rose.
At its biggest, Santarosae joined San Miguel, Santa Rosa, Santa Cruz and Anacapa into one landmass several times the size of those four islands today. Scientists are still finding evidence of what lived there.
Map depicting the reconstructed geography of Santarosae.
Anacapa broke off first, around 10,300 to 10,900 years ago, when the sea covered the narrow neck of land connecting it. People watched it happen. Humans were already living on Santarosae by 12,710 to 13,010 years ago, maybe earlier, and they probably got there by boat, following the “kelp highway”, a chain of rich kelp forests running along the coast from Japan and Kamchatka, past Beringia and down to Baja California. For people traveling that route, Santarosae would have looked like a land of plenty.
Its most famous residents were pygmy mammoths, found nowhere else. They stood about 4.5 to 7 feet tall at the shoulder and weighed around 2,000 pounds, shrunken versions of mainland Columbian mammoths about the size of a big horse (see our story on the island biogeography of the Channel Islands). Big animals stuck on islands, with limited food and no big predators, tend to shrink over generations, a pattern called the island rule. The pygmy mammoths disappeared around 13,000 years ago, right as the climate was changing and people were arriving.
Pygmy Mammoth excavation on the Channel Islands (NPS)
The first “elephant” bones on Santa Rosa Island were reported in 1873. Digs there in 1927 and 1928 turned up enough to name a new species, Mammuthus exilis. In the 1940s and 1950s, Philip Orr of the Santa Barbara Museum of Natural History found many more.
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Most pygmy mammoth fossils have come from Santa Rosa and San Miguel, with fewer from Santa Cruz.
Santarosae was also home to some of the earliest people known in North America. In 1959, Phil Orr found human bones on Santa Rosa Island that turned out to be about 13,000 years old, among the oldest in the Americas. They were first thought to be a woman’s, but later analysis suggested a man, now known as Arlington Springs Man. The island’s early people fished, hunted seals and birds, and gathered shellfish and plants, and they had to be good on the water to get there at all. Thousands of years later, their successors, the Chumash, built the famous plank canoes, called tomols, that they used to travel between the islands and the mainland.
Archaeologists excavate a anthropological site at the Channel Islands (NPS)
The islanders weren’t cut off, either. Tools and materials found there came from far away, part of a trade network along the California coast. As the sea rose and their land shrank, they had to adapt.
The Ice Age island looked nothing like today’s Channel Islands. Cool, moist forests covered much of it, with hills, valleys and fresh water. As the climate warmed, the forests shrank and the land turned into the windswept, scrubby terrain you see today.
Anacapa Island today (Erik Olsen)
Some animals, like the mammoths, didn’t make it through those changes, or the human hunters. Others adapted to the smaller islands and kept evolving, which is how you end up with things like the island fox.
Today what’s left of Santarosae is protected as part of Channel Islands National Park, and archaeologists and biologists are still piecing its story together.
Tourists now enjoy the natural beauty of the Channel Islands (Erik Olsen)
When you take the boat out to Santa Rosa or Santa Cruz now, you’re sailing over the drowned valleys of Santarosae. It’s a good reminder that the coastline we think of as permanent is just where the sea happens to be right now.
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