I believe the answer is 6 mile squares. Hope this was helpful.
Primary source documents :)
Answer:
Samuel F.B. Morse, in full Samuel Finley Breese Morse, (born April 27, 1791, Charlestown, Massachusetts, U.S.—died April 2, 1872, New York, New York), American painter and inventor who developed an electric telegraph (1832–35). In 1838 he and his friend Alfred Vail developed the Morse Code.
Answer:
The Rocky Mountains.
Explanation:
The Great Plains are around the middle of the US and end western at the Rocky Mountains
