none
it is entirely artificial
California is North of California's southern border, and Oregon is North of California's northern border.
The mountains on the northern border of Italy are known as the Alps. They make a natural boundary between Switzerland and Italy.
The northern boundary of New Hampshire is defined by the Canada–United States border, specifically the state of Quebec. This boundary runs approximately 58 miles from the Connecticut River in the west to the Atlantic Ocean in the east. The border is characterized by a mix of forests and mountainous terrain, reflecting the natural landscape of the region.
It is the southern border for Texas; conversely, it is the northern border for Mexico.
Maryland's northern boundary is defined by the Mason-Dixon Line, which serves as the border between Maryland and Pennsylvania.
Manitoba has a border on Hudson Bay.
Most of the northern boundary is formed by the Alps. However, on the Iberian Peninsula, the Pyrenees form another northern border of Southern Europe.
The sea that forms the northern boundary of Africa is the Mediterranean Sea. The countries of Morocco, Algeria, Tunisia, Libya and Egypt border it.
A natural boundary is a boundary that is viewed from a physical factor like a mountain, river, or other land form/waterway. A political boundary is a boundary that is man made or decided by people. For example the state border is a political boundary.
The Missouri River forms a boundary between the states of Missouri and Kansas. It serves as a natural border in the region, particularly in the area around the Kansas City metropolitan area. Additionally, it also acts as a boundary between Missouri and Nebraska at its northern end.
mediterranean sea
Rio Grande