By the end of the 18th Century, the vast majority of what is now the continental United States was still largely unexplored. The 1803 Louisiana Purchase was the catalyst for what is now recognised as one of the most important land explorations ever mounted.

A few weeks after the purchase, President Thomas Jefferson had the U.S. Congress appropriate $2500 "to send intelligent officers with ten or twelve men to explore even to the western ocean."

On May 14, 1804, under the shared command of Captain Meriwether Lewis and Second Lieutenant William Clark, the Corps of Discovery left their base at Saint Charles, Missouri, and didn't return until September 23, 1806.

The attachment contains:

• a series of general placemarks showing the journey west, with links to the revelant parts of the Discovering Lewis and Clark website
  
• the routes the Corps took during preparation, recruitment and west- and east-bound exploration
  
• a more detailed set of placemarks with descriptive metadata
  
• a polygon outline showing the boundaries of the Louisiana Purchase
  

The attachment is only viewable with the Google Earth (beta) client. For those of you who haven't yet received your invitations, be patient. And for those of you who have been invited, but haven't installed it ... this is a pretty good excuse.