The Last Crystal Trilogy
The Trilogy started backward. We were visiting family in Sacramento when I learned that my Uncle-in-Law, Frank, had made a train trip every summer to visit grandparents. His father worked for the railroad. So he and his little brother were put on the train to travel from Missouri to California alone. All sorts of possibilities came to mind. Book 3, written first, begins on the Santa Fe Chief. Book 1, The Black Alabaster Box begins on the Santa Fe Trail.
The Black Alabaster Box
It had been quiet along the Santa Fe Trail for more than a year when the Stokes Company set out for California in the early 1840s, the Willis family among them. A reluctant traveler, twelve-year-old Grace Willis longs for her fortunate, safe and comfortable life at home. Just as she is learning to negotiate life on the trail, Grace is kidnapped by fellow travellers and taken into Oklahoma Territory. She must decide if she will cave in to despair or muster the courage to run away and search for her parents. Grace finds help in unlikely places. She discovers that there really is such a thing as magic and there are some things only a child can do.
You can read more about the development of the book on the author's blog: https://fourleavesandtales.blog