A boy is talking to someone through a thick, grilled fence. At first, you can't tell who's on the other side, but if you look closely, you can make out an older man in a blue checked shirt.

The boy is David Vargas. The man on the other side of the fence is his grandfather.

"Are you coming next week?" David asks.

"Maybe Friday I'll be there," Ignacio Vargas says through the fence. "All I have to do is just jump the fence, right?"

Short of jumping, the only way Vargas can touch his grandson is by sticking his pinky through the fence. David touches it with his own pinky, and they wiggle fingers.

Once a week, David Vargas visits his grandfather who's on the Mexican side of the border. They touch pinkies to 'hug.' (Kim Brunhuber/CBC News)

That's how they hug. They'll do this again next week.

"Agridulce," Vargas calls it. Bittersweet.

That's become the theme here at Friendship Park, a section of the border at Border Field State Park, south of San Diego. It was inaugurated in the 1970s to promote friendship between the U.S. and Mexico. The irony now rises 5½ metres high in the form of a massive border fence.

A man in a large hat is translating a Bible passage that his colleague across the fence is reading in Spanish. Every Sunday, they meet here and offer simultaneous communion on both sides of the border in a service called The Border Church.

Rev. John Fanestil translates a passage from the Bible that's being read by his colleague on the Mexican side of the border. (Kim Brunhuber/CBC)

"The border is as much a bridge as a barrier for those who live near it," Rev. John Fanestil says.

On the U.S. side, a handful of devotees listen to the Scripture. It's hard to see how many Mexicans are listening on the other side.

Fanestil shows pictures taken in 2008 when he first started Border Church.

"The fence was much more open," he says. "And you could see that families could have meals here, exchange gifts, and we were able to serve communion by passing the elements through the fence. But then when they put up the heavy grill, between 2009 and 2011, they told us it was illegal to pass anything through the fence."

When he started the weekly border service in 2008, Fanestil could pass the sacrament across the border to share it with those in Mexico. But six years later, they have to do separate communion services. (Kim Brunhuber/CBC)

He prepares the sacrament on a blanket on the ground, while his Mexican colleague does the same on the other side of the fence. They'll share it, separately. The devotees on either side offer blessings by laying their hands on the fence.

"I'm hoping that my presence and the presence of the church would help to preserve access, so that families and friends would still be able to meet at this location," Fanestil says.

There's a massive door in the middle of the fence; an emergency door informally known as the Door of Hope. It was last opened on April 30 for Children's Day, when members of selected families that have been separated for years were allowed to pass through and briefly reunite.

Two children play between two sets of border fences near San Diego (Kim Brunhuber/CBC)

Those who weren't lucky enough to be selected, like Valeriano Valdovinos Sr., can only see their children through the fence. The conditions of his work permit don't allow him to leave the U.S. and his son can't get a visa.

"I'd like to give him a hug," Valdovinos says in Spanish. "I could touch his finger, I could feel his heat through the gate."

He pauses, then smiles wanly.

"It's better than nothing."

Valeriano Valdovinos came to visit his son, whom he hadn't seen in nine years. He says feeling his son's warmth through the fence is 'better than nothing.' (Kim Brunhuber/CBC)

It may be heartbreaking, but it's still one of the few places in the country where Mexicans and Americans can see and speak to each other in person along the border wall.

The first thing you notice about the wall is it's not really a wall. In most places — like farther east, across from the Mexican city of Tecate — it's actually a fence. The second thing is, in some places, it's not all that high. A six-foot tall reporter can stretch his arms out and touch the top. It seems simple to get over, but with cameras, infrared equipment, and other high-tech devices, it wouldn't take long for border patrol to find an intruder.

Less than a third of the U.S. border with Mexico has fencing. So far, the U.S. has spent more than $7 billion on border fences. (Kim Brunhuber/CBC)

Twenty years ago, border patrol arrested more than 550,000 people along the border between California and Mexico in one year. Last year, it was down to 40,000.

Even though less than one-third of the country's 3,200-kilometre border with Mexico is fenced, the U.S. has spent more than $7 billion on fences, not including maintenance. And the average cost to build new fencing, according to the Government Accountability Office, is $2 million per kilometre.

Twenty years ago, border patrol agents in California arrested more than 550,000 people. Last year, the total was about 40,000. (Kim Brunhuber/CBC)

California holds its Democratic and Republican presidential primaries today. The presumptive Republican nominee, real estate mogul and reality TV star Donald Trump, has vowed to build a stronger and taller border wall with Mexico.

"It's gonna be a real wall," he said last August. "Not a toy wall like we have now."

Some who live near the border say there are already too many walls.

"You used to be able to go right out onto the beach," says longtime San Diego-area resident Tom Antoniewicz, pointing to a section of beach at the Tijuana border.

"People on both sides of the border could walk through the fence. You could meet, you could talk with them, you could shake hands … That's what made America great. Not these walls," he says of the newly built fence that extends into the surf.

Tom Antoniewicz says he's ashamed to see the wall because his money helped build it. (Kim Brunhuber/CBC)

"This is what makes us pathetic," he says. "I'm literally ashamed when I see this because it's my money that built that wall."

Celeste Caton, 25, agrees.

She came to Friendship Park to visit the friends she made when she spent two years in Tijuana.

"Makes me sad to be part of this side where they consider it as much of their home as I do mine," Caton says.

She says one of her friends was deported and forced to leave her two children behind.

A common sight along the border: Mexican towns grow right up to the fence, whereas the U.S. side is often wilderness. (Kim Brunhuber/CBC)

"My heart does break for them and hopes for the day they'll be able to stand where my two feet are," Caton says.

Farther down the fence, Alejandro Vera is seeing his mother for the first time in 15 years.

He drove from Los Angeles with his family. His 71-year-old mother flew all the way from Mexico City just to meet at the fence and touch.

Cactus grow on the other side of the border fence in Tecate. (Kim Brunhuber/CBC)

He reflects on the moment as he walks back to his car, carrying his son on his shoulders.

"That was an emotional moment," Vera says. "At the same time it's sad. Very sad."

He has friends who moved to the U.S. and never saw their parents again. He says he had to feel his mother's warmth, perhaps for the last time.

A military crest from a unit that worked on this part of the border fence. (Kim Brunhuber/CBC)

"I just touched my pinky finger, that's it." Vera says. "It was really important to me."

Agridulce.

And with that, visiting time at Friendship Park is over.

On the Mexican side, they run into the sea to fish and swim. On the U.S. side, a border patrol car is parked on the beach. Watching.