Possibly NV-CA, possibly TX-OK, both about 700 miles. I think that TX-OK might be longer but sources are vague and varying.
The longest border separating two countries is the 8,891 kilometers (5,525 miles) boundary between Canada and the United States. It is the world's longest international border between two countries.
The longest border separating two countries is between Canada and the United States, stretching for about 5,525 miles (8,891 kilometers).
the longest in one country is the Great Wall of China
USA and Canada - 8,893 km (including: 2,477 km with Alaska)
Hawaii and Alaska are two states that do not border any other state in the United States. Hawaii is located in the Pacific Ocean, while Alaska is separated from the contiguous states by Canada.
Virginia, of which West Virginia was part until the Civil War, has the longest border, to the south and southeast. The border with Ohio on the west is the second longest.
The longest border separating two countries is the 8,891 kilometers (5,525 miles) boundary between Canada and the United States. It is the world's longest international border between two countries.
California and Nevada
Idaho and Montana
Kansas and Oklahoma
Oregon and Washington
Montana and Wyoming
The longest border separating two countries is between Canada and the United States, stretching for about 5,525 miles (8,891 kilometers).
New Mexico and Texas
Nebraska and South Dakota
Virginia and West Virginia
The same state that has the second longest shoreline of all fifty states ... Michigan.