In the planning phase, the word “pilgrimage” never came to mind.

But well before our 3,033-mile meander from Denver to San Francisco ended, I realized this trip was much more than a long vacation.

My husband and I had talked about visiting the West for several years, so when the opportunity presented itself — through an invitation from our son-in-law’s parents to their home near Rocky Mountain National Park and a family wedding near Yosemite — filling in the wide open spaces between the bookends seemed a felicitous course of action.

From our first hike at Rocky Mountain, in north-central Colorado, through tours of three ancient settlements in the Four Corners region, then on to more national parks in east-central Utah and eastern Nevada before reaching California and Yosemite, the wonders over the two weeks along the way held me in a momentous grasp. Even as sentimental as I can be, never in my 55 years had I found myself so daily overwhelmed with awe and gratitude for my own country’s gifts to the world. The seven national parks we experienced were but a sample of all the system preserves, celebrates and showcases. But, in joining the millions of Americans and international visitors who come to the parks each year, my husband and I explored places that transcend today’s troubling political and racial divisions, recurring violence and environmental threats to remind us all about the importance of beauty, of where we’ve come from as people and as a planet.

Sacred places, is what they are. That’s where pilgrims go — even accidental ones.

Celebrating a centennial

This year, as the National Park Service celebrates its centennial, the 59 national parks, 81 national monuments and dozens of other park service sites of historic, military and recreational value are continuing a long-term trend of ever higher numbers of visitors. In 2015, more than 307 million visitors traveled to National Park Service sites — a number not far off from the total U.S. population of about 322 million. That number, said Jeffrey Olson, spokesman for the parks service, reflects individual visits — the same person could pass through the north rim gate at the Grand Canyon, for example, five times during a weeklong vacation, and would be counted as five visitors. Still, the steady upward trend over the last decade, which slipped only in the year of the government shutdown in 2013, shows no sign of abating.

“Everybody likes us, regardless of political party,” one ranger told us.

So far in 2016, Olson said, the numbers are on track to spike by 3.5 percent over 2015 — no small number when the total is already more than 300 million. What’s drawing so many people to Acadia and Mount Rainier, Denali and the Everglades, and all the great places in between?

“It’s about discovering your home, your history, and family, family, family,” said Olson. The 100th anniversary this year also has sparked new attention to the parks, including from President Barack Obama, who hiked Yosemite with his wife and daughters in June and spoke beforehand about how a boyhood visit to Yellowstone changed him. Lingering reverberations from the Ken Burns-Dayton Duncan documentary, “The National Parks: America’s Best Idea,” which first aired seven years ago, are also responsible, Olson said. My husband and I watched all six episodes before our trip, the best TV-watching time we’ve spent in many years.

Starting at Rocky Mountain — the third busiest park in the system — we were fortunate to have local hosts to take us to a less-traveled corner, the high tundra where delicate alpine blossoms color the earth amid patches of glacial ice, ancient crags and cliffs black as night save for tufts of green moss. Marmots poked up out of the rocks to fatten themselves on flower heads in preparation for their winter’s nap in burrows. Hoping to see the elusive bighorn sheep the park is known for, I had to settle instead for spotting several piles of their dung. But several elk and a big bull moose dining on an aspen sapling did cross our path on other trails. Several times, just staring at the mountain vistas along the hikes or even out of the car window would force me to choke back tears I didn’t want to unleash with abandon. Am I really here? Better save those emotions for private moments later.

From Rocky Mountain, we drove our rental car to southwest Colorado. A photo of the cliff dwellings at Mesa Verde in my elementary school social studies book had stuck with me all these years. Now I would get to see them for myself. At the Air B&B residence where we stayed for four nights, our welcoming hosts shared with us their own story of moving from Wisconsin to teach at Native American reservation schools, then settling permanently on a small farm where they grow hay and spinach for local restaurants and keep chickens while teaching at local public high schools. We learned from them about the irrigation farming of the area and the nearby reservoir created in the 1970s that flooded some ancient ruins. Pottery and other artifacts literally were yanked from the site in some pell-mell emergency archaeology that filled a local museum.

At Mesa Verde the next day, we first signed up for the guided tour of the Balcony House cliff dwelling later that morning, then drove the steep, switch-back road to the top of Chapin Mesa. There, we marveled at Spruce Tree House and learned about the people who once dwelt in this canyon from the dioramas, pottery, tools, scraps of cotton cloth, sandals, tools and leggings woven from the feathers of turkeys — their only domesticated animal — in the museum. At the waiting area for the start of the Balcony House tour, one of the many engaging and enthusiastic park rangers we met put what we were about to see in context. The remains of the communities built within the shelter of the sandstone alcoves were alive with families some 1,000 years ago, before the signing of the Magna Carta, before Columbus, Shakespeare, Newton and many other of the major milestones of Western civilization. Another ranger, Drew Regan, led the tour, reminding us that we would need to be able to scale 32-foot step ladders, climb through a tunnel, and, most important, treat the dwelling as a sacred place that is someone’s home. That, he said, is what the modern Pueblo who are descendants of the former occupants have emphasized when he takes them through the site to incorporate their knowledge and interpretations into his narrative.

Inside Balcony House, as the group gathered around the circular kiva where the ancient people once held ceremonies, a Danish visitor brought his own cultural context to what he was seeing. In his country, he mused, it was the era of the Vikings at the time the Mesa Verde cliff dwellers farmed, built amazing villages and traded jewelry, pottery, woven goods and other items with neighbors and more distant communities.

At the end of the day, after taking in several of the self-guided sites, we left Mesa Verde and began making plans to go the next day to a remote corner of New Mexico, to the Chaco Culture National Historical Park where the settlement remains predate those at Mesa Verde. It’s a place I’d been wanting to visit since my 20s, when I read Willa Cather’s “Song of the Lark” and Chaco figured as the scene of a turning point for the main character. After a long drive that ended with 13 slow miles on a rutted dirt road, we made it to what became my favorite of all the fabulous places we saw. From the petroglyphs aligned with the solstice on the butte at one end of this city that once thrived with trade in Mexican chocolate, parrots, copper bells and shells, to the rock walls carved for better acoustics across the canyon, to the doorways and chambers of the homes and plazas, Chaco is fascinating. Ranger G.B. Cornucopia, who led a tour of the Chetro Ketl great house, told us what’s known about Chaco — and what isn’t. There’s still a lot of mystery about why people settled here, how they lived — evidence of farming in this dry area is scant, at best — and why they left. But clearly, he noted, this was once a prospering society, one that had the time and resources to build great structures, create caches of beautifully decorated pottery and feed their people from goods brought in from elsewhere. Like his colleague at Mesa Verde, Ranger Cornucopia said he also brings contemporary Native American groups through Chaco, and shares their stories with visitors.

Well before the tour began, though, I was already feeling astonished. On a short hike to one of the ruins shortly after we arrived, I looked at the dirt floor in one of the rooms and spotted a potsherd, with the characteristic black-and-white geometric design of the ancient dwellers. In that moment, I was experiencing my own version of the scene from “Song of the Lark.” Taking photos but leaving the shard, still a bit breathless, my husband and I headed up a trail through a canyon crevice used as a passage since ancient times to a magnificent overlook.

Later, after the tour, my husband showed the ranger a photo of the potsherd.

“They come up all the time when it rains,” he replied.

When we arrived back at the Air B&B, I told our hostess, Angie, about the potsherd. Appreciating my excitement, she gave me two from her own collection of potsherds that had come up in her garden over the years. These gifts from the ancient peoples are just a part of life here, she said. Her neighbor has ruins in his backyard. Some of the old sandstone bricks were even used for roadbeds. Call me corny, or even mawkish, but I treasure these two vessel fragments as priceless objects once held in hands that are reaching out across the centuries.

Next on our trip came Hovenweep, officially a National Monument site instead of a park, but every bit as worthwhile as the others we saw. Located in southern Utah, it preserves an intriguing collection of 800-year-old towers and homes. All are different in style from those at Mesa Verde or Chaco — including one built inside an eroded boulder — and all are built of sienna-colored bricks cut from canyon stone that contrast beautifully against the deep blue southwestern sky. Like Mesa Verde and Chaco, Hovenweep left me with new curiosity and admiration for the native peoples of this country, past and present.

The road to Yosemite

But much more was ahead. When it came time to start the drive to Yosemite, we settled on a route with stops at Arches in Utah and Great Basin in Nevada, vastly different landscapes equally different in their drawing power. At Arches, erosion and weathering have sculpted a Martian landscape of spires, arches, pinnacles and enormous pedestals of red rock in the desert that attracted about 1.4 million visitors in 2015 — roughly 10 times as many as Great Basin. The sights at Arches are truly amazing and worth seeing — even with the many other tourists and effective temperatures that reached 140 degrees at one of the arches, owing to the heat from the blazing sun radiating off the bare rocks.

At Great Basin, in the lush, green mountains of eastern Nevada — a world apart from the seemingly endless deserts of the rest of the state — we skipped the tour of the most popular feature, the Lehman Caves, for a hike to the bristlecone pine grove near the top of Wheeler Peak. These 3,000-year-old, sinuous evergreens are the oldest living things on earth, managing to hang on to life since the time of the ancient Phoenicians despite the harsh high-altitude environment.

Crossing Nevada, we covered miles of flat desert mostly empty of other cars and human life, driving a straight road into the horizon that felt jarring to our Northeastern sense of distance. After staying the night in the old silver mining town of Tonopah, we set out for our last leg of the journey to Yosemite. But just outside of Tonopah, a surprising sight rose from the desert landscape. Crescent Dunes, a huge solar plant that uses mirrors and molten salt to collect and store energy, sent out blinding light from its central receiving tower. It gave me new hope for the future of renewable energy, a welcome thought as we headed to the place where the conservation movement began with John Muir and the Sierra Club at Yosemite.

At Yosemite, we hiked with other family members to majestic redwoods and misty Bridalveil Falls, feasted on views of El Capitan and Half Dome, and savored the sight of a Chinese family joining hands around an enormous pine. A bobcat slipped into sight along the Upper Yosemite Falls Trail, just as our exploring was nearing the end — at least for now. The day before, we had been in the Tuolumne Meadows part of Yosemite, enjoying a free concert and hearing Ranger Margaret Eissler speak movingly about how she grew up in a small log cabin just a few dozen yards away, with no running water or electricity. Her father had been a ranger at Yosemite, and now, as the chill breezes of fall were already starting to blow in this alpine meadow, we had all gathered in the place where national parks began to celebrate a century of inspiring awe. What a privilege to be part of this.

National parks in New England

As part of its 100th anniversary celebration, the National Parks Service is offering free admission to all its parks from Aug. 25 to 28.

National Parks sites in the six New England states, New York and New Jersey include:

Multi state: Appalachian Trail; New England Trail; Washington-Rochambeau National Historic Trail; Blackstone River Valley

Connecticut: Weir Farm National Historic Site

Rhode Island: Roger Williams National Memorial; Touro Synagogue National Historic Site

Massachusetts: Adams National Historic Park; Boston National Historic Park; Cape Cod National Seashore; Lowell National Historic Park; Minute Man National Historic Park; New Bedford Whaling National Historic Park; Salem Maritime National Historic Park

Vermont: Marsh-Billings-Rockefeller National Historic Park

New Hampshire: Saint-Gaudens National Historic Site

Maine: Acadia National Park; Roosevelt Campobello International Park; Saint Croix Island International Historic Site

New York and New Jersey: Vanderbilt Mansion National Historic Site, Eleanor Roosevelt National Historic Site, Home of Franklin D. Roosevelt, Ellis Island and the Statue of Liberty; Niagara Falls National Heritage Area; Women's Rights National Historic Park, Lower East Side Tenement Museum; Sagamore Hill; Saratoga National Historic Park

For information about the parks and special events for the centennial, visit www.nps.gov.