Read: The Edge of the Earth by Christina Schwarz, 2013, 9781451683677.
Committee book. Not too bad.
Short version: Spoiled girl in 1890s Milwaukee marries a bum, moves to CA, husband takes job at lighthouse, woman starts scientific study and intrigue ensues.
Long version: Trudy is the child of a prosperous tugboat owner in Milwaukee. She has been attending a woman's college (with a curriculum that is more of a finishing school). Trudy has a scientific bent but is scheduled to marry the son of family friends. Her fiancee's cousin, Oskar, comes to live in Milwaukee. The cousin and Trudy fall for each other, marry, and head out to California. Trudy gets clues about Oskar's flighty, impulsive behavior and wishful thinking when he pawns some of her belongings in San Francisco.
Oskar gets hired as assistant lighthouse keeper at remote Point Lucia on the CA coast. The lighthouse is manned by Mr. Crawley who lives there with his wife and four kids and his brother-in-law, Mr. Johnston. The lighthouse is several days ride from civilization and is resupplied every 3-4 months. The ships have no place to dock and anchor offshore and send in longboats. Oskar, Mr. Crawley, and Mr. Johnston have daily shifts to man and maintain the lighthouse equipment.
The island is windswept and lonely by Trudy manages pretty well. Oskar has big plans to invent and build electrical equipment but his intelligence is not up to the task. Mrs. Crawley is grouchy but Trudy likes the kids and is drafted as school teacher. Trudy starts studying tidal pools and the creatures within. Trudy mails a former teacher offering samples. Trudy and Mrs. Crawley start selling tidal pool samples through the mail.
One day Trudy discovers that a woman is leaving in a cave among the shore. Trudy finds the woman was discovered by loggers living alone in the woods. Wild Woman was presumed last Indian of a tribe and taken by Mrs. Crawley. Mr. Johnston leers for Wild Woman, gets her pregnant, and Wild Woman skips out to hide in the caves.
There is some mystery about a dead infant. About Wild Woman who the kids think is a mermaid. By Oskar who is intent on studying Wild Woman and is posing as a scholar by stealing Wild Woman's stuff and scheming to kidnap her to UC-Berkley. A couple people drown and everyone lives happily ever after.