A new law went into effect on July 20, 2011 that allows Arizona to build its own fence along the Mexico border. State lawmakers who supported the law have said they want a continuous fence along the entire border. The state's southern border is about 370 miles long. About a third of that, mostly in the western part of the state between Yuma and Nogales, has the type of fence lawmakers want. In those parts of the state, the fence is only a few feet tall and is made of barbed wire or wooden posts. Most illegal immigrants cross into the eastern part of Arizona over that more porous border.