I have been a student of Lewis & Clark and the Corps of Discovery since I was a kid growing up in St. Louis.
I'll list several other books on the expedition.
Bernard Devoto, "The Journals of Lewis and Clark."
Landon Y. Jones, "William Clark and the Shaping of the West"
Also by Jones " The Essential Lewis and Clark.
Larry E. Morris, "The Fate of the Corps." What became of the Lewis and Clark Explorers after the Expedition.
Carol Lynn MacGregor, "The Journals of Patrick Gass" Member of the Lewis and Clark Expedition.
Willard Sterne Randall, "Thomas Jefferson A Life" (I'm still trying my best to finish this.)
Also another great easy read by Stephen E. Ambrose is "Nothing like it in the world" The men who built the transcontinental railroad 1863-1869.
Anyone who lives in California, Nevada, Utah, Wyoming or Nebraska and can travel along this route and you can in most places by following I-80, should feel the history of westward expansion. It's just remarkable what they did with pick, shovel, rod and chain.
Bob