The final borders of the lower 48 states were established in the?

The last purchase that defined the border with Mexico was made in 1853 west of the Rio Grande and south of the Gila River and is known as the Gadsden Purchase. That will not be the end of the story since rivers do change their course from time to time and the courts are required to decide the case. Geographic irregularities include:

• The Northwest Angle.
• The Delaware Wedge.
• Iowa's Carter Lake.
• The Toledo War.
• The Massachusetts Jog.
• Vermont's Alburgh.
• Point Roberts, Washington.
• The Country Club Dispute which went to the Supreme Court in 1927.