A remarkable telling of a remarkable journey taken by remarkable people. I am sure there are countless works of fiction on both the Corps of Discovery and Sacajawea. I haven't read any of them so I'm certainly no authority, but I think this has to be one of the best - certainly one of the best aimed at young readers. The book's best feature is it's dual narrative - each chapter alternates between the perspectives of Sacajawea and Captain Clark. Sacajawea's chapters are the strongest and most engaging, but Clark's chapters still do their part to flesh out the details. All of Sacajawea's chapters begin with a short Native American legend and all of Clark's with an excerpt from a journal entry. Highly recommended!
*A note on recommended age: the back of the book and amazon both say 12 and up - likely due to advanced vocabulary as well as some slightly mature themes (just one example of many - Lewis's sad end is told in more graphic detail than one might expect). Still I always say one can go a bit younger when reading. I read this with my ten year old and she enjoyed it mightily!