Using Google Earth, I took a couple of snap shots of the Border @ Tiajuana. I notice that there is some odd distortion in the pic where the US side starts and have pointed it out.

The yellow line represents the border.

I will leave it up to you to decide on which side is the US.

http://www.awcorg.us/images/misc/tijuana-2.gif

http://www.awcorg.us/images/misc/tijuana-1b.gif