The Mississippi River was the western border in 1787.
Pacific
Mississippi River
Pacific
Pacific Ocean
The Mississippi River
Yukon Territory
the state of Texas
The Pacific Ocean
The Pacific Ocean.
The Appalachian Mountains marked the Western border of the newly-founded USA.
Idaho has a border with six US States plus Canada. Oklahoma has a border with six US States. Utah has a border with six US States. Wyoming has a border with six US States.