I like to think of these books as kind of a cross between the Little House series and Little Women. Or, perhaps more accurately, a cross between the shows Dr. Quinn and Touched by an Angel. Yes, this trilogy is the book form of the love child between those two shows!
It's mostly about a brother and sister who cross the country during the civil war/building of the transcontinental railroad with their Irish sister-in-law to take her to her brother in California. Then they get involved in the building of the railroad.
The brother they were meeting in California, Kiernan, and his wife (the sister), Victoria, were by far the most interesting characters to me and they played a smaller role in these books. They almost weren't in the 3rd one at all. The third one was also very teenage angsty for me - "Does he love me?" "Do I love him?" "Does she love me?" "Do I love her?" and it got old very fast. This is why I don't like book Katniss.
But I would absolutely recommend these books to anyone who has a current or nostalgic love of Dr. Quinn and/or Touched by an Angel. Or if you're into American historical fiction 🙂