In 1806 President Thomas Jefferson sent cartographer Thomas Freeman and botanist Peter Custis to explore the southen Louisiana Purchase westward to the Rocky Moutnains. Stopped by a Spanish army in what is today extreme southern Oklahoma, they did not complete their mission. President Jefferson minimized their failure by focusing instead on the success of their northern counterparts Lewis and Clark. Hence the fame of Lewis and Clark and the virtual anonymity of Freeman and Custis-until now, thanks to editor Dan L. Flores.

Dan Flores presents the primary documents created by Freeman and...