By Franc Contreras
The BBC's The World programme, Tijuana, Mexico
An intense debate is under way in the United States over what to do about illegal immigration. The Senate is soon to take up the issue, studying a controversial bill that would see the construction of 1,130km (700 miles) of fencing along parts of the border with Mexico.
People along the western edge of the border, south of San Diego, have been living with a barrier for the past 16 years. Franc Contreras travelled there to ask people on both sides what the divide means to them.
A series of rusty iron panels separate this part of the US from Mexico. On the US side of the border, many people call it "the fence".
More barriers like this one could go up on the border
Muriel Watson, who was largely responsible for getting the barrier built, says that before it went up in 1990, this part of the border was wide open.
"There was nothing here. There were some streetlights up there from that Mexican freeway, but as you can see, it's all open fields over there, and when the sun went down, all hell broke loose."
Hundreds, and sometimes thousands of illegal immigrants crossed through here into southern California - Mexicans and Central Americans fleeing poverty and unemployment in their countries.
Ms Watson decided to take action, and in 1989 she organised a movement called Light up the Border.
Dozens of supporters came in their cars to the desert.
They turned on their headlights, shedding light on the situation. The media and Congress quickly took notice. Within a year the barrier went up.
'Sign of respect'
"We knew it was not going to stop everything. But it was the first time in history that anyone knew where the actual international border truly was - they would know if they crossed over that they were breaking the law. So that was important," Ms Watson says.
Stadium lights are now in place, and there are 10 times more border patrol agents on duty than in 1990. Illegal crossings at this part of the border have dramatically decreased.
For Ms Watson, widow of a former border patrol chief, the fence is a sign of respect.
"That fence tells you that's your side, and this is ours. If you want to violate that, that's your choice, but it's our right to say there's a fence," she says.
"Good neighbours have good fences... Nobody gets bent out of shape because of a fence, it's strictly a line of demarcation and respect for the owners on each side."
Over the years, more fencing has been added along this part of the border. It now stretches about 40km (25 miles) from the rugged Tecate mountains to
the Pacific Ocean.
In Tijuana, children play on the sandy beaches.
This is the farthest point of northern Mexico - and for that matter, Latin America. Here, the divide is known as "el muro", or the wall.
In the past few weeks, the US has been rebuilding the metal fence, eroded by the salty sea air.
The new divide is made of railroad tracks plunged deep into the sand, sticking some six metres (20ft) up in the air.
And where the old barrier and the new one meet, there is a gap.
In broad daylight, small groups of Mexicans are going through it. A little girl grabs her mother by the hand and both step into the US. A retired man called Enrique Manzo also tries it.
He says it is the first time he has ever set foot on US soil. Mr Manzo, who is in Tijuana visiting relatives, says he cannot wait to tell his son back home about this remarkable moment.
Most of the people say they are happy to be in their own country. They had no reason for getting a visa, so for a brief moment they cross the border barrier illegally.
But for a few, it is not the first time.
Alicia Flores explains that she crossed the border illegally a few years back. Her smugglers led her through a hole in the fence on this very same beach.
She worked for six years in California, then returned to Mexico. She thinks the barrier is divisive.
Antonio Ortega leans on the barrier. He calls it a monument to American racism.
"The strongest ones show their power with things like this wall, but it doesn't prevent people from crossing," he says.
"Most now take the dangerous routes through the desert or over the mountains."
Mr Ortega himself made that difficult journey. After 11 failed attempts he finally made it into the US.
But not everyone on the Mexican side has such strong views.
Further to the east is the border city of Mexicali.
Retired accountant Francisco Perez says the people on this part of the border have also lived many years with a barrier dividing them, but for him it is no big deal.
"It doesn't affect me because I've had good work here. Besides, I never think of going to live in the US," he says.
Like many Mexicans who live in border communities, Mr Perez has a special visa that allows him to enter the US legally whenever he wants.
He does not think building more barriers will solve the issue of illegal immigration from Mexico. But he does expect the political rhetoric both sides of the border to continue.
That is a safe guess. The US holds Congressional elections in November. Mexicans will vote for a new president in July.
And immigration is a campaign issue in both countries.