This is a book in the tradition of Mark Twain, told by a boy of eleven with excerpts from his father's journal as well, which fills in some of the things that a child would not have noticed or known about. Jamie is a Huck Finn character, averse to school and book learning, loving adventure, and open to putting aside the bigotry that he has grown up with. I would not be surprised to learn that this book might have inspired some later historical fiction authors like Paulette Giles and Gary Paulsen.
Jamie's father, a medical doctor educated in Scotland, has an unfortunate relationship with gambling, often brought on by too much to drink. He is a dreamer, always looking for the main chance, and when he decides that the gold in California is just waiting for him to find it, he plans a cross-country trip and takes Jamie with him. Between the two of them they document their adventures on the trail in great detail, and the author acknowledges that he has based the book on some actual journals, and historical figures like Jim Bridger and Brigham Young make appearances. Since the first reading when I was a teenager I had forgotten just how realistic the writing is, with some pretty gory details.
It's not hard to see why this book won a Pulitzer Prize; it is a masterpiece of historical fiction, and I would love to see it recognized again.