Along the California-Mexico border (CNN) The borderlands of California and Mexico change dramatically as one drives toward the Pacific Ocean. The Imperial Sand Dunes give way to majestic mountain peaks and, eventually, the lush hills of San Diego.

The scenery reminded me of what Big Bend National Park ranger Michael Ryan told us hundreds of miles before we reached this part of the southern border.

"It's not just one border," Ryan said. "It changes, depending on where you are."

Ryan has lived along the southern border for nearly 30 years. But after a nearly 2,000-mile journey from south Texas to where the southern border reaches the Pacific Ocean, it seemed like Ryan's words just don't refer to the physical changes.

The southern border is a dynamic environment, culturally and environmentally. It's constantly evolving.

Uncertainty in the borderlands

Pedro Rios leads the San Diego chapter of the American Friends Service Committee, a social justice organization focused on helping immigrants in southern California. Rios says the beginning of the Donald Trump presidency has ushered in the next new era of uncertainty for the borderlands.

"There's a lot of tension," Rios said. "A lot of fears, because in the past, when the border becomes a target, it's an excuse to increase enforcement, (and) the people who live on the border suffer."

It's here in this southwest corner of California where the San Diego metropolitan area hits the Mexican border where the dramatic changes of the border are crystal clear.

On the other side of the border is Tijuana, a sprawling and vibrant city of 1.3 million people. Residents say in recent years the wait times to cross the ports of entry into the United States can take as long as 5 hours on some days.

This section of the U.S.-Mexico border is one of the most heavily fortified sections where the border wall has been doubled up in some places. But here, Homeland Security agents are battling smugglers -- not just above ground but below ground as well.

The San Diego sector is home to a band of Border Patrol agents known as the "Tunnel Rats." This team specializes in uncovering and investigating underground tunnels used to smuggle massive loads of drugs into the United States.

The Galvez tunnel was discovered by U.S authorities in 2009.

Lance LeNoir, a US Border Patrol operations officer leading the sector's "Tunnel Rats" team, is taking our CNN crew deep inside one of these tunnels.

"The imagination of people trying to come north is something I don't try to second guess. (It is) incredible some of the methods they use," LeNoir said.

To reach the bottom of what's known as the Galvez tunnel, we take a series of four steel ladders straight down a 70-foot shaft.

When we reach the bottom, the air is muggy and one of the first things you see is a makeshift distance marker humorously telling you that Mexico is 8 feet to the south and San Diego is 40 miles to the north.

The Galvez tunnel was discovered in 2009. It was dug from a warehouse that we can see just beyond the border fence and extended about 760 feet to the north toward another warehouse on the US side of the border.

A makeshift distance marker in a tunnel wryly gives some vital distance numbers.

LeNoir said the tunnel was never fully completed, but it speaks to the ingenuity and brute strength used to dig these tunnels under the border walls. The tunnel was cut through jagged rock and measured about 6 feet tall and 4 feet wide.

"They (drug smugglers) are looking for bulk transport," LeNoir said.

This tunnel was equipped with a rail system and electricity. The agent says the tunnels are usually used to move massive loads of marijuana and cocaine.

"We recognize digging crews," he said. "They all have their unique shape, size and little nuances that you pick up."

Juan Munoz, Homeland Security investigations special agent, says in the last 10 years nearly 30 tunnels have been discovered in the San Diego area alone.

Munoz says these tunnels are usually found connecting between commercial warehouses, but that to discover these tunnels requires intense investigative work and intelligence information.

"They will continue to go on between the Mexican and US border," Munoz said. "If there's a way that these drug trafficking organizations can stay undetected, and it's by tunneling, they will."

LeNoir says the tunnels have grown more sophisticated as border security above ground as become more elaborate and extensive.

"This is usually high dollar-high risk reward enterprise," Lenoir said. "It's a lot of stuff that they have to move in a small amount of time."

But as the arsenal of border security tools has grown and appears that it will grow even larger during the Trump administration, border residents worry about the toll this will take on their communities.

Photos: Views from the border The US-Mexico border spans 1,933 miles. It runs from the Pacific Ocean to the Gulf of Mexico, across California, Arizona, New Mexico and Texas. President Trump's pledge to build a wall along the border was a key part of his campaign. He said this month that early construction of the wall would be funded with US tax dollars in order to get started quickly, and promised that Mexico "will reimburse us." Click through this gallery to see scenes from the border and perspectives from those who live and work near it. Hide Caption 1 of 20 Photos: Views from the border Pamela Taylor, 88, has lived in Brownsville, Texas, since 1947. Taylor says she has had people from "all over the world" arrive on her property, and she says she has even found them in her living room. Every night, she fills a cooler in front of her house with bottles of water for migrants who made the journey, Border Patrol officers, or anybody else who finds themselves near the front steps of her house. Hide Caption 2 of 20 Photos: Views from the border Taylor put this sign up down the road from her house during the 2016 presidential election. She says that the fence the US government put up near her property in 2007 doesn't work. "I would like for Mr. Trump, I would even feed him, if he will come down here and talk to the people," Taylor told CNN. "He is doing exactly what the government did to us in the beginning. He's not asking how it's going to affect the people that live here." Hide Caption 3 of 20 Photos: Views from the border The Rio Grande forms a border between Texas and Mexico. Much of the river straddles remote desert and farmland, such as this stretch in Progreso Lakes, Texas. Hide Caption 4 of 20 Photos: Views from the border On October, 26, 2006, President George W. Bush signed the Secure Fence Act, and said, "This bill I'm about to sign is an important step in our nation's efforts to secure our border and reform our immigration system." More than 1,250 miles of the border are in Texas, but the state only has about 100 miles of man-made borders. This fence line in Progreso Lakes, Texas, comes to an end, and leaves miles of border land open. Hide Caption 5 of 20 Photos: Views from the border Greg Henington, owner of Far Flung Outdoor Center in Terlingua, Texas, says he doesn't believe a wall is necessary. "The wall is not going to make a difference one way or another. It's just going to cost a ton of money and look dumb." Hide Caption 6 of 20 Photos: Views from the border In 1935, the federal government passed legislation that would enable the state of Texas to acquire the land that would become Big Bend National Park. The park, known for its remote beauty, shares the border with Mexico for 118 miles and is separated by the Rio Grande. Hide Caption 7 of 20 Photos: Views from the border Lilia Falcon owns Jose Falcon's restaurant in Boquillas del Carmen, Mexico, across the Rio Grande from Big Bend National Park in Texas. The border crossing closed after September 11, 2001, and reopened in April 2013. "This town just went dead," Falcon told CNN. "We are very happy that the border is reopened again. We feel very safe here, even tourists that come over here, the word is spreading out more that its very safe to come here." Hide Caption 8 of 20 Photos: Views from the border Many Texas residents in the Big Bend National Park region believe that the various miles of remote canyons and rivers already act as an "effective barrier" with Mexico. Hide Caption 9 of 20 Photos: Views from the border Robert Cameron, owner of Texas Border Tours in Progreso Lakes, Texas, is in favor of President Trump's proposed wall, but he knows it will be complicated to build through parts with rough terrain. "I want to see a wall," Cameron told CNN. "Not a fence. I want to see a wall. I want to see something that you can't see through, that you can't climb through." Hide Caption 10 of 20 Photos: Views from the border The scenic mountains, canyons and desert that make up the Big Bend region on the west Texas-Mexico border span an elevation of less than 1,800 feet near the Rio Grande to almost 8,000 feet in the Chisos Mountains. Hide Caption 11 of 20 Photos: Views from the border Michael Ryan has worked as a ranger at Big Bend National Park since 1999, and 10 years as a river guide in the region previously. "It's not just one border, it changes depending on where you are," he told CNN. Hide Caption 12 of 20 Photos: Views from the border The Boquillas Crossing, a one-of-a kind port of entry where you can take a small ferry boat across the Rio Grande and into the tiny Mexican village, reopened on April 10, 2013, following federal closure for more than a decade after the September 11, 2001, attacks. Hide Caption 13 of 20 Photos: Views from the border Marcos Paredes has lived near Terlingua, Texas -- a former "ghost town" -- for much of his life. He spent years as a law enforcement officer responsible for patrolling the Rio Grande. "To come up with a one-sized fits all solution for illegal immigration is crazy," Paredes told CNN. "Because the border is so different along its entire links." Hide Caption 14 of 20 Photos: Views from the border Alicia Bon Martin, born in Nogales, Mexico, and her husband, Chris Martin, work and live on both sides of the Arizona-Mexico border. They own organic farms in Mexico, a produce distributorship, and the restaurant La Roca, a Nogales, Sonora, institution started by Alicia's uncle and celebrating its 45th year anniversary this year. "We are lucky because we have the good things of both sides," Alicia told CNN. "I see this border as a much calmer than anybody portrays it to be." Hide Caption 15 of 20 Photos: Views from the border Tim Foley founded The Arizona Border Recon in 2011, a nongovernment organization which provides intelligence to the US Customs and Border Protection. Foley has set up about a dozen cameras in the Sasabe, Arizona, desert and shares a database of smuggling activity that he says he captures with the Border Patrol. "It's a huge game of hide and seek," Foley told CNN. "A wall might help a little bit. But we have a wall here, or a fence, or whatever you want to call it. And it's not a deterrent -- it just slows them down for 10 seconds. So unless you have people watching the wall, it's not going to do anything. You need boots on the ground." Hide Caption 16 of 20 Photos: Views from the border There are about 700 miles of fence along the 1,933-mile international US-Mexico boundary. This stretch in Sasabe, Arizona, has a fence that was built in 2007. "I think a barrier, a physical barrier, is definitely necessary," Shawn Moran, vice president of The National Border Patrol Council, told CNN. "Putting up a fence, putting up a wall, has stopped the vehicle loads from coming across the border. It has been almost 100% effective in doing that." Hide Caption 17 of 20 Photos: Views from the border The westernmost part of the U.S.-Mexico border overlooks the Pacific Ocean, inside California's Border Field State Park outside San Diego, and adjacent to a public beach in Tijuana, Mexico. This area is known as Friendship Park/El Parque de la Amistad, a historic meeting place where generations from both nations have gathered to visit with family and friends "across the line." Hide Caption 18 of 20 Photos: Views from the border The Galvez tunnel was discovered by US authorities in 2009, approximately 20 yards north of the national boundary in Otay Mesa, California. The tunnel is about 6 feet high, 4 feet wide, and goes about 70 feet below Earth's surface. According to Homeland Security Investigations special agent Juan Munoz, their San Diego-based task force has discovered more than 29 of these sophisticated tunnels in the past decade. Hide Caption 19 of 20 Photos: Views from the border A US Customs and Border Protection officer patrols the fence in Otay Mesa, California. Patched holes in the fence are a common sight along this section of the border next to Tijuana, Mexico. Hide Caption 20 of 20

Changing communities

Alicia and Chris Martin live on the US side of the border and have businesses on both sides. They own La Roca restaurant in Nogales, Mexico -- south of Tucson and near the Arizona border. In addition to their restaurant, they own organic farmland in Mexico and a produce distribution business.

They have seen how the charm and simplicity of border life has slowly eroded away.

Alicia and Chris Martin own La Roca restaurant in Nogales, Mexico.

Alicia Martin recalls the days, as a young girl, when a group of friends would freely run across the border to buy ice cream from a vendor on the Mexican side of the border.

"We would just walk across, wave at the guy and go back. That's it," Alicia Martin said. "So this thing of a line. A border. A fence. A wall. I mean it doesn't compute for us."

Those days are long gone, and the Martins know it's not coming back either.

The US State Department warns that the Mexican state of Sonora, which includes Nogales, is a "key region in the international drug and human trafficking trades," and encourages American citizens to limit travel to main roads during daylight hours.

But the Martins stress that the neighborhoods around their restaurant are safe, and say that because the borderlands are often painted as a wild and dangerous place it hurts development and growth.

After September 11, when border security became a higher priority, the Martins say intensified immigration controls and the fear of border violence dramatically effected tourism to Nogales.

"It was like somebody came in and flipped a switch. There was nobody in town," Martin said.

La Roca struggled to keep its doors open. Alicia Martin's uncle opened the restaurant 45 years ago and the thought of going out of business was painful. The couple held on and now they're starting to see business and the energy of this border town come back to life.

With diplomatic tensions between the Trump administration and the Mexican government starting to escalate, the Martins worry about what will happen next.

Chris Martin argues that throwing up trade barriers, dismantling NAFTA and building walls will only bring back more depressing days.

"They are such harsh approaches. You are treating a symptom," Chris Martin said. "It's education, it's economic security, it's economic strength that is going to keep people from migrating in droves from one country to another."