Instead of four separate islands, they formed a single large landmass.

Researchers call this ancient superisland Santarosae.

It was roughly 125 kilometers long and at its maximum extent substantially larger than any of today’s individual Channel Islands.

It had peaks where today’s islands have peaks, canyons where today’s islands have canyons, and a coastline that extended across areas now submerged.

By 13,000 years ago — the approximate date of the Arlington Springs individual — sea level had risen from its glacial-maximum low but had not yet reached the modern position.

The channel separating Santarosae from the California mainland was narrower than today.