Friendship Park. The name has a lovely ring to it, conjuring up images of families playing together joyfully. The reality is far grimmer; an 18-foot galvanised metal fence – fortified with sensors, lighting, radars and cameras – that keeps family members apart.

The park in San Diego is the only spot in the US-Mexico border fence where people can speak to friends, family members and lovers on the other side – under heavy security at severely restricted weekend hours. The mesh fence has tiny holes in it, allowing people to get a glimpse of each other, and perhaps put a little finger through to touch them.

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Gabriella Ramirez, 23, speaks to her boyfriend, a construction worker who emigrated to CaliforniaJohn Moore/Getty Images
Mexico Freedom Park
Mexicans stand on a beach in Tijuana while looking through the border fence into the United StatesJohn Moore/Getty Images
Mexico Freedom Park
Gabriella Ramirez, 23, speaks to her boyfriend, a construction worker who emigrated to CaliforniaJohn Moore/Getty Images
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A US Border Patrol agent takes a selfie at the fenceJohn Moore/Getty Images
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Family members touch through the US-Mexico border fenceJohn Moore/Getty Images
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A woman shows loved ones a photo through the US-Mexico border fenceJohn Moore/Getty Images
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Karen Herrera, 23, holds her three-month-old baby Ivan while speaking with family members through the US-Mexico border fence. She said she has been living in California for a year, having applied for political asylum after her husband was murdered in TijuanaJohn Moore/Getty Images
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A woman looks through the border fence from Tijuana into the USJohn Moore/Getty Images

It was all supposed to be very different. Friendship Park was opened by First Lady Pat Nixon in August 1971 as part of her efforts to promote US-Mexican relations. As she shook hands with Mexicans that day, she was reported as saying: "I hope there won't be a fence here too long. I hate to see a fence anywhere."

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First lady Pat Nixon shakes hands with Mexicans through strands of barbed wire as she visits Friendship Park in August 1971US National Archives and Records Administration

The park allowed access for people on both sides of the frontier, with picnic tables and swings. It was a place for cross-border weddings, church services, Christmas parties and even yoga classes. In 1994 the United States raised a mesh fence to stop drug traffickers and illegal immigrants, but families could sit on either side of the fence to kiss through it, talk and touch one another, even as US border agents nearby patrolled to keep out job-hungry illegal immigrants, terrorists and smugglers. The fence became a popular spot for separated lovers, who would pass notes on Valentine's Day.

In 2009, the US closed the park and built a second larger barrier, sealing off access for Mexicans on the US side unless they take part in highly regulated visits. The authorities allow access to the original border fence for just four hours on Saturdays and Sundays, in groups of up to 25 people who have been vetted by US agents.

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A mural which reads "We Are America" is seen on the Mexican side of the border fence, as a US Border Patrol camera tower stands tall on the American sideJohn Moore/Getty Images
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Deported family members of "Dreamers" and their supporters pray at the border fence in Tijuana. "Dreamers" are US-born American citizen children of undocumented immigrants, many of whom were deported back to their home countriesJohn Moore/Getty Images
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Juana Saravia Medina, 60, speaks to her daughter and grandchildren through the fenceJohn Moore/Getty Images

On Saturday 30 April – Children's Day in Mexico – authorities opened a gate in the fence for only the third time since it was built. Six pre-screened families were allowed to spend three minutes together, closely watched by US Border Patrol agents. The families were then ushered back to their side and the gate was closed again.

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US Border Patrol agents open a door in the fence for only the third timeJohn Moore/Getty Images
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Family members embrace under US Border Patrol supervision during the Opening the Door of Hope eventJohn Moore/Getty Images
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Samantha Simental, 3, walks to meet family members from Mexico as the border gate is openedJohn Moore/Getty Images
Mexico Freedom Park
A US Border Patrol agent stands guard as families prepare to meet loved ones when the gate is briefly openedJohn Moore/Getty Images
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A woman hugs a child as families are allowed to meet for three minutesJohn Moore/Getty Images
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Relatives embrace at the US-Mexico border fence during the "Opening the Door of Hope" eventJohn Moore/Getty Images
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Samantha Simental, 3, cries after meeting family members from MexicoJohn Moore/Getty Images
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A Mexican boy hits a Captain America pinata as part of Mexican Children's Day celebrationsJohn Moore/Getty Images

It is estimated that about 12 million illegal immigrants, mostly Hispanic, live and work in the United States, including millions of Mexicans. If Republican presidential candidate – and now presumptive nominee – Donald Trump gets his way, the fence will be replaced by a wall and families won't even get a brief glimpse of each other.