You never know whom you might meet on an Eastside trail—a lesson I learned several weeks ago above Duck Lake in the John Muir Wilderness, when I bumped into Seuk Doo Kim, a Korean hiking guidebook author.

Kim was hiking with a large party that had assembled in the shade just over Duck Pass. But Kim, an avid hiker, and his wife, Sun Ae Kim, had continued on alone to the far end of the lake and back.

The two are 77 years old.

“We are the oldest on the trail,” Kim told me with pride.

The pair has been hiking in their native Korea and in the United States since they were married. Kim called this the secret to a long, healthy marriage: “Hike together,” he said.

Kim recently completed a hiking guidebook, Korea Baekdu-daegan Trail Book, which will come out in October.

Unbeknownst to me—and perhaps many others—the Baekdu-daegan is a continuous mountain range running from Mount Baekdu (9,003 feet above sea level) on the northern border of the Korean Peninsula down to Mount Jiri (6,283 feet) near the southern end. The distance between the two is 1,008 miles. About half of that distance is in South Korea.

Kim notes in an English forward to his Korean-language guidebook that the other half of the trail cannot be reached due to a fence dividing the North and South, but, he writes, “We must pursue the ideal of hiking the entire Baekdu-daegan as both a physical journey and a spiritual one.”

In fact, the mountain range, though never broken, was not considered in its totality until recently. During what South Koreans call the “Japanese Imperial Period” (1910-1945), Japanese geologists grouped mountain ranges according to their geological nature instead of terrain and ridgeline. This grouping was intended to aid the development of mining and road construction, Kim writes.

Learning this history affirmed Kim’s resolve to educate his fellow Koreans about the complete mountain range and trail.

From 2008-2011, Kim and his wife made annual trips to Korea to complete the roughly 600 miles of the South Korean portion of the Baekdu-daegan trail (that’s almost three times as long as the John Muir Trail, and about a fifth as long as the Pacific Crest Trail).

At the age of 74, the couple became the oldest to complete the trail.

Seuk Doo Kim had another motive behind completing the trail and writing the guidebook, he said: a desire to reconnect his children to their home country.

Kim moved from Korea to Los Angeles 33 years ago, when he was appointed deputy general manager of the L.A. branch of the Bank of Seoul, but he realized after many years that his children were losing touch with their home country.

“I determined that I have to do something in order to prevent my son’s patriotism from becoming thin,” he writes. “I had to make action for family.”

Kim’s sons, daughters, grandsons, and granddaughters all joined him on a hike to the top of Mt. Jiri during his time composing material for the guidebook.

But the Kims haven’t confined their explorations to Korea, as I learned when I met them above Duck Lake. Kim said he frequently goes on hikes with his two grandsons in the San Gabriel Mountains near his home in Culver City, and has even taken his grandchildren hiking on portions of the Appalachian Trail.

Perhaps most impressively, Kim said he has climbed the Iron Mountain, an 8.5-mile trail gaining 6,000 feet to the top of the 8,007-foot peak in the San Gabriel Mountains, 100 times in an eight-month period last year.

According to the Sierra Club Hundred Peaks Section, Iron Mountain is considered to be the hardest climb in the San Gabriels because of its treacherous terrain, lack of maintained trails, and steep slope.

Kim also hiked Mt. Whitney in 2008, at the age of 70.

But Kim had never before visited Mammoth Lakes.

“This was my first time hiking up,” he told me. “Most hikers stop on the trail a third or half the way … If only they had experienced up to Duck Lake. The water is clean and the view is same on the top of Duck Lake as the Baekdu-daegan Trail. I feel at home. The view is like paradise!”