'Grandma Joy' and her grandson share snapshots of America as they try to visit all 61 national parks

For the last four years, Brad Ryan and his grandmother Joy Ryan have been on the road trip of a lifetime, attempting to visit all 61 national parks and inadvertently giving all of us a true tour of the U.S. in all of its natural beauty.

So far, the pair have traveled 40,000 miles through 41 of the lower 48 states and taken in the scenery at 49 national parks.

On Friday, they were wrapping up a trip to Gateway Arch National Park in St. Louis -- their 49th and final park in the lower 48 states.

Before Gateway, there was the Grand Canyon, Yellowstone, Joshua Tree, Glacier National Park and even Redwood National Park.

"It is breathtaking," Joy Ryan, 89, told ABC News recently from the Santa Elena Canyon in Texas' Big Bend National Park. "All of these people are really enjoying it."

"We'll have to come back here and explore it some time," Brad Ryan said.

The duo started in 2015 and were at Great Smoky Mountains National Park in Tennessee when Joy Ryan, then 85, spent the first night in a tent.

Brad Ryan, 38, said she'd spent the majority of her life in the tiny town of Duncan Falls, Ohio.

"She had never camped a night in her life," he told ABC News previously. "When we arrived at 1 a.m. in the rain...she held the umbrella over my head while I put the tent together."

At the time, Brad was a fourth-year veterinary student at the Ohio State University College of Veterinary Medicine, but he said he needed a break.

"I remembered a prior conversation with my Grandma Joy when we [were] discussing my 2009 Appalachian Trail hike from Georgia to Maine, and she expressed regret that she had never seen the mountains and explored the great outdoors throughout her life. So, I invited her to join me on my weekend escape to the Smokies," he told ABC News in a previous interview.

Big Bend National Park was the 47th U.S. national park for the duo. On this last road trip, Hyatt Hotels provided lodging for the two.

"We can't believe that we're closing in on that 61 national park goal and we're having a wonderful time here in Texas," Brad Ryan told ABC News. "This is definitely one of the prettiest parks that we've seen so far. Big Bend National Park has Badlands. It has canyons. It has the mighty Rio Grande River, and so much wildlife and beautiful fauna and flora that we really feel like we might have to come back for a second go."

"We've met some wonderful people," Joy Ryan added. "Everywhere you look you see something beautiful. ... This is a great place."

On Friday, Joy Ryan said she was ready to take a much-needed break before the next adventure.

"I am ready," she said, "to go home, kick back my heels and sit down and rest a minute."