Sacajawea by Anna Waldo is now available as an ebook. Its about the native American woman who accompanied Lewis and Clark's Corps of Discovery and is often credited with the success of their mission. It was a huge bestseller in the 80s ("Huge" as in a 1400 page paperback).
There are a few scholars who maintain that Sacajawea did not die in 1812 but left her family in St. Louis to return to the West and lived until 1884. The novels follows this line and speculates on her later life.
http://inkmesh.com/ebooks/sacajawea-.../?qs=sacajawea