what feature makes up part of the u.s. border with canada?

what feature makes up much of the u.s. border with mexico?

http://www.worldatlas.com/webimage/countrys/namerica/ca.htm

Notice the land and water forms at the right.

http://www.worldatlas.com/webimage/countrys/namerica/mx.htm
The straight lines that make up the western half (left) of this border are surveyed lines that run through the open deserts, but that curvy line that makes up the eastern half (right) of this border is what river?
http://en.wikipedia.org/wiki/Rio_Grande_border_disputes