WEST GLACIER — These mountains have always been old, weighed heavy with age and rooted in deep time, the kind of place where you can heft a handful of early, early earth and wonder at the world before.

Rippled rock at 10,000 feet is sediment laid down 1.6 billion years ago, the oldest rock there is — Proterozoic history heaved up some 170 million years back when the Rocky Mountains pushed skyward.

A sheet of stone three miles thick and 160 miles long crashed eastward then, advancing 50 miles and folding old rock over new, creating the block from which vast chisels of ice would carve what we now know as Glacier National Park.

“That’s what people have always come to see in the park,” Leigh Welling said. “They came to look into the past, to see something pristine. To me, the park’s first century was defined by a certain stability.”

“You could count on it,” Welling said. “The mountains and the depth of nature seemed very long-lived. They’d always been here, and always would be here.”

But now, Welling said, here at the brink of Glacier Park’s 100th birthday, “we’ve come to a very interesting turning point. If the first century was defined by the past and by stability, then the second century is the exact opposite.

“Now, we’re looking at the future, and at remarkable instability. Now, all of a sudden, we’re faced with how fragile a system like this can be.”

Welling is founding director of Glacier’s scientific clearinghouse, the Crown of the Continent Research Learning Center, and so knows a bit about this age-old mountain ecosystem. But she’s moved on now, has taken the lead as the National Park Service’s climate change coordinator, and so also knows a bit about how this ecosystem is shifting.

“We’ve always gone to nature because it is so huge and we are so little,” Welling said. “We’ve gone to feel humble, and to put ourselves in perspective. But today, when we go, we’re also reminded that we actually affect everything. There’s not a place on the planet that we haven’t touched. Not even a wilderness like Glacier.”

Glacier Park begins its second century at a time of tremendous change climate change, visitor change, budget change and the next 100 years, Welling said, will look very different from the first 100.

The park already is positioning itself to deal with these new realities, and is emerging as an impressive leader in many ways both in terms of internal action and external education but “no amount of preparation will ready us for what’s to come,” she said.

It’s more than just melting glaciers — those will be gone in 30 years or so. It’s also increasingly powerful wildfires and avalanches, warmer waters, drier streambeds, overheated critters. And it’s more visitors demanding more services at a critical time of smaller budgets. It’s endangered rangers and a growing moat of development that rings the protected park island.

“Hold on to your hat,” Welling advised, “because by mid-century things are really going to start changing here, in ways we’ll all see and feel directly.”

Glacier National Park is not just old, it’s big. So big that it’s hard to imagine we could put so much as a dent in it. A full million acres and then some, 760 lakes, 560 streams flowing a combined 2,865 miles. Two million visitors on more than 700 miles of trail, sharing space with 25 different species of fish, 75 mammals, 250 species of birds, and nearly 2,000 different kinds of plants.

People have called it home for more than 10,000 years, with the first Europeans arriving only about two centuries ago. Members of the Lewis and Clark expedition came close in 1806, and were fast followed by fur trappers.

The railroad — which billed the area as “America’s Switzerland” and eventually would build much of the park’s early infrastructure — crossed the mountains here in 1891, bringing homesteaders and, later, tourists.

The travelers rode the Great Northern to West Glacier — then named Belton — and hopped a stagecoach to the foot of Lake McDonald. From there, a boat ferried them eight miles to the Snyder Hotel.

On May 11, 1910, President William Taft signed the paperwork to make this park a park, and in the following year some 4,000 people came through the gates. They rode horseback through the wilderness, traveling from one backcountry chalet to the next, as engineers down below went to work on park roads.

The famed Going-to-the-Sun Road crossed the Continental Divide in 1932, making this its 75th birthday. It is a time of anniversary, in fact, with the Glacier-Waterton International Peace Park also marking 75 years last summer. In 2010, the park turns 100, and in 2016 the National Park Service cracks the century mark.

“But there are some constants throughout all that time,” said Will Hammerquist, who runs the local office of the National Parks Conservation Association. “The main constant is that Americans love their national parks, and they especially love Glacier National Park.”

Another constant is the constant struggle for funding, which spans Glacier’s centennial. “These are national treasures,” Hammerquist said of parks, “and funding them should be a national priority.”

He’s hopeful, though, that all these anniversaries might provide the push the parks need. The Centennial Act, if approved, would allocate $100 million in public money to match dollar-for-dollar with private donations between now and the Park Service’s big birthday in 2016 — $1.6 billion over the next eight years.

And the Centennial Initiative would, if approved, restore national park operating budgets that Hammerquist said “have been flat or on the decline for many, many years.”

Today, the annual shortfall is estimated at more than $2 billion, with park maintenance backlogs many times more than that.

“Parks like Glacier are the anchor stores of our economy,” Hammerquist said, “and it makes sense to invest in them. The centennial is a good time to be thinking about how to do that.”

The way Hammerquist sees it, “we’re going to have to make some tough choices in Glacier’s second century.”

It’s a question, really, of how well we can accept the notion of impermanence in a place so old and permanent.

“What we have here is a learning moment, and we’re trying to capitalize on that,” said the park’s centennial coordinator, Kass Hardy. “We have glaciers that are receding, and infrastructure that is deteriorating, and more visitors all the time. This is tangible stuff. People can touch it, they can see it with their own eyes.”

And that, she said, is what makes this moment this birthday so very important. It’s the hands-on impetus to begin doing things differently, both within Glacier’s bureaucracy and as part of the educational outreach to its visitors.

“What we really want is to use the centennial to create programs that last well into the future,” Hardy said. “We don’t want a crazy sugar buzz up to 2010 that’s just going to crash in 2011. We need to keep our eyes on the long-term future here.”

Just as visitors in that first century had their eyes locked squarely on the long-ago past.

Click here to visit the Missoulian's Web site for more coverage of Glacier's upcoming 100th anniversary.