As the British colonies on the eastern seaboard became more populated in the mid-1700s, colonists began to look beyond the Appalachian Mountains and contemplate westward expansion. Looking westward, they could only imagine the incredible riches the continent would offer to them. Not much information was known about the territory west of the Appalachians. A 1795 map did offer a fairly accurate picture of the western region of North America, but it mistakenly depicted several inland lakes as being considerably larger than the Great Salt Lake. The map's cartographers probably drew these lakes from vague reports they had received from Indians. In 1806 John Cary produced a map that accurately depicted the Pacific coastline, but he did not include inland details—which resulted in a map that left blank almost the entire region west of the Mississippi River.

Curious to know more specifically what the western...