The novel is based on the true story of Juana Maria, the "Lone Woman of San Nicolas Island", a Nicoleño Indian left alone for 18 years on San Nicolas Island, one of the Channel Islands, off the California coast before being "rescued" in 1853.
One version of Juana Maria's story is she lived with others of her tribe on the island, and then a Russian ship brought Alaskan Aleuts to the island to hunt otter, after which the Aleuts killed all the men on the island and made the women their slaves. Ultimately either the women killed the men as revenge or the Russian ship came back and took the Aleuts away. The Santa Barbara Mission then sent a ship to pick up the women left on the island, and a ship picked them all up and took off. Juana Maria, however, could not find her brother and asked the ship to turn around, but since it wouldn't, she jumped ship to swim back for her brother, who was dead, having been eaten by dogs.
Another variation of the story has the boat leaving, but she is in the mountains trying to get her baby, and a storm brews and they leave without her.
Juana Maria ends up alone on the island for 18 years. She lived in a hut made of whale bones and seal skins, she had made two dresses out of bird feathers and skins with bone needles and seal sinew thread, she took birds from the rocks at night for food, she got water on the island from a spring. She was found and brought back to Santa Barbara in 1853. She died weeks after being brought to Santa Barbara and is buried at the Santa Barbara Mission