The border between Mexico and the United States has been the subject of much debate in this year's US presidential election.

Americans go to the polls on November 8, and if Republican presidential candidate Donald Trump wins, he has promised to seal the around 2,000-mile (3,200-kilometer) border between US and Mexico with a wall.

In parts of California and Arizona, a wall already exists, and it splits towns and families, marking a boundary between the US and Mexico.

It runs across rocky deserts, flowing sand dunes and miles of agricultural land.

Busy land ports of entry and signs written in both Spanish and English attest to an interdependence that still exists in the bifurcated cities, faded mining towns and eccentric art outposts that punctuate the arid landscape.

Ground sensors, cameras and hundreds of customs and border patrol officers are used to monitored the border.

In Nogales, Arizona's largest international border community, the wall neatly divides the city. Little else distinguishes the hillside homes stacked on either side.

Some who live near the border in California and Arizona agree with Trump and his demand that Mexico pay the cost for construction of a wall on the border between the two countries. Others are deeply disturbed by it, like Mexico's government.

"It's been stigmatized pretty bad," said Jaime Alvarez, a retired Army auditor running for Arizona Senate. He works out of the Democratic party office in the city of Douglas.

Alvarez said residents are worried that too much talk about border control will distract people from having other important discussions about education, poverty and healthcare.