Island of the Blue Dolphins is based on the true story of The Lone Woman of San Nicolas Island, who lived alone for eighteen years. Unlike Karana, she returned to the island to stay with her child, not her brother. She's buried near the Santa Barbara Mission in California (source).
Scott O'Dell lived in Southern California, an area that inspired many of his books, including Island of the Blue Dolphin. He writes, "That is why, I suppose, the sound of the sea and the feel of the frontier are in my books. And why many of the people I have written about are Indians, Spaniards, and Chicanos" (source).
Scott O'Dell's was named Odell Gabriel Scott. He changed it to Scott O'Dell as an adult (source).
Scott O'Dell did not originally mean for Island of the Blue Dolphins to be a children's book. It wasn't until he showed the manuscript to a friend that he was told that kids would like it (source).
Scott O'Dell wrote a sequel to the novel called Zia, which was published in 1976. The book tells the story of Karana's young niece who is on a quest to find her aunt on the island (source).