Alicia Z. Klepeis 
Lewis y Clark y la compra de la Luisiana (Lewis and Clark and Exploring the Louisiana Purchase) [PDF ebook] 

When President Thomas Jefferson bought the Louisiana Territory from cash-strapped France in 1803, he doubled the size of the United States without really knowing what he was getting. He dispatched Meriwether Lewis and William Clark and their Corps of Discovery to explore a territory that would include part or all of fifteen future states and to seek a water route to the West Coast. Westward expansion began immediately, all for the bargain price of 15 million dollars. This book richly explores this fascinating part of history.