Fairbanks simply stops and Alaska takes off into the wilderness, stretching unbroken all the way to the Arctic Ocean. From our antique DC-3, the solid, green forest changed gradually to scattered, glittering shapes: Sun reflected off the treacherous labyrinth of the Yukon Flats.
Then the great river itself curled into view. Although it is legendary for the tumultuous aftermath of the gold strike at Fortymile in 1886, the real significance of the Yukon River lies in prehistory. It was the path to the Americas from the Bering Strait, an ice-free refuge as glaciers closed in on each side.
The beauty of the flight silenced the chatter of our group - seven members of a Mountain Travel trek and two leaders. The plane took us over the razorlike mountains of the Brooks Range, over the rectangular patterning of the Arctic tundra - the result of hundreds of years of freeze-and-thaw cycles - then dipped toward a tiny cluster of houses at the treeless edge of the continent.
Smiling faces met the plane, faces nestled in wolverine fur. Our group stepped off into a sunny June afternoon and a windy 36 degrees - 21/2 hours by plane from the 90-degree heat of Fairbanks.
Kaktovik is a village of people who are known in English as Eskimos but who call themselves Inupiat, ''the real people.'' The houses are ''ranches'' now rather than the underground sod dwellings of 20 years ago. But the close connections of the Inupiat and the animals with which they share this forbidding land are still visible everywhere. Strips of seal meat hang on drying racks in front of houses. In one yard, 10-foot lengths of baleen lie against some rusting drums with the brown filaments billowing in the wind. The hide of a polar bear is stretched on a roof to dry.
Great space stretches in every direction, with nothing on the flat horizon but chunks of ice crushed into a ridge at the shore - and on the ridge the carcass of a whale.
Is it possible that this is still the United States? For the 19th-century explorers, the Arctic was the culmination of a long and perilous voyage; such a remote, strange country needs to be earned. But a noticeable feature of Kaktovik is the line of telephone poles. And over the small wooden turquoise box of a post office - ZIP Code 99747 - flies the American flag.
Seventy miles south of Kaktovik, in a valley just below Mt. Michelson and the continental divide, trip leader Chuck Horner tried to teach us how to walk without rushing; to wait, upon reaching a rise; and then scan for animals, the Inupiat way. And by the end of the trip, we were doing it. Richard Nelson describes it in ''Shadow of the Hunter'': ''They had learned the gift of enduring patience. . . . One could not expect that the weather, ice, and animals would do a man's bidding.''
Sometimes we walked on miniature flowers, a lush variety of genus, shape, and color, matted together into a spongy insulating blanket over the permafrost - solid here to depths of 2,000 feet. At other times we followed bear and caribou trails.
The land is much more rugged than it looks. It consists of tussocks held together by complex root systems above the soggy tip of the permafrost. Walking any distance means crossing streams of tremendous velocity, the runoff of water unlocked by summer and unable to seep into ground that is as solid as bedrock.
But walking here has its rewards: the tracks of a wolf still sharp in wet sand lying astride our way; the scent of willow catkins filling the air; Dall sheep, their heavy curled horns balanced over dainty legs, moving across impossible scree.
In the perpetual day, it is hot by 6 a.m., and we swim in the ice water of a glacial tarn. But by noon there can be thunder in the clouds piling up on the mountains and a temperature drop of 40 degrees.
Late in the afternoon of our first full day in the Brooks, we saw what we had come for: a caribou, alone, coming directly through camp. It walked slowly at first, and then shifted. With head as erect as a show horse, it pranced by, chin up, antlers spread flying behind as if blown back by the wind.
There is no airstrip here; the tiny plane that took us out landed on the stones of the dry creek bed. After five days in the Arctic, an airplane is a sophistication, a reality that makes no sense.
We spent a second week in Denali National Park. Denali is an Athabaskan Indian name that means ''the great one.'' Mt. McKinley rises higher from the land around it than any mountain in the world - 19,000 feet above the Chulitna River.
McKinley is a new mountain. The whole Alaska Range is being thrust up as the North American tectonic plate grates over the Pacific. There are almost nine vertical miles between the Aleutian Trench where the Pacific plate is disappearing and the summit of McKinley. Geology is immediate here, and the Pleistocene is not far away. The very oldest rocks in Alaska stand next to the newest in Denali, and round pebbles washed into old seabeds form solid strata high on mountainsides.
You can see great distances here. The whole of the vast Muldrow Glacier is visible - 40 miles long, spread out like a textbook. Past periods of advance are evident by ridges in the moraine. In 1956 the glacier surged forward six miles and was pressed into a turn by the opposite wall of the valley. It is awing to look at this apparently inert mass of ice and to contemplate its having moved that winter at a rate of 10 inches a minute.
As we entered the park, we stopped to watch a herd of caribou browsing in a meadow. Suddenly we saw a wolf near the herd. It assessed the situation. Then, crouching, moved in by degrees, hidden from them by a rise. It sprang into a run. Heads up, racks flying, the caribous stampeded. But they did not run far - the hunt continued. A few animals strayed slightly from the rest. This time, the wolf ran flat out after them. Eventually it gave up, loped across the meadow, and dropped down, sniffing the wind.
The Inupiat have a saying: ''It is the wolf that keeps the caribou strong. The wolf and the caribou are one.'' This time there were no weak animals to cull.
We stayed at Camp Denali, just north of Wonder Lake, with what is renowned as the most spectacular view of McKinley. Small buses carried us from the train across the expanse of park - with guides who not only hold advanced degrees in geology and ornithology but who also have an acquaintance with the area.
Guided hikes of graduated difficulty leave every morning. I remember crossing a steep triangle of unstable scree, colored improbably with an occasional red and yellow flower, a black pond, and a single red-throated loon trailing a wake of silver.
On our last day, a small group of us took a ''flight-seeing'' tour of Mt. McKinley and were let off 10 miles from camp for a ridge hike. Over us was open blue, with gray clouds crowded on the horizon. Our feet sank a foot into the moss. In the enveloping silence, we heard the liquid sound of an American golden plover - just yards away from us.
At the end of the ridge, we looked down over Moose Creek, a sinuous river, winding in a long tendril back over our path.
That morning we had had a different view of Moose Creek. We had passed a gold-mining operation which, at ground level, had looked like a small thing despite the backhoe, the sluicing machine, and two Caterpillar rigs. From here, we could see a whole section of Moose Creek turned into red raw dirt - both banks scoured for yards, the river uprooted.
I had spoken with the mining-operation owner. ''There's a lot of gold in Alaska. They didn't even scratch the surface - only went down 4 feet. We go down 30 or 40.'' He will mine the whole length of Moose Creek, then move on to the other miles of claims he holds. ''I plan to be mining 50 years.''
The guide saw my face and said with quiet irony: ''There's a lot of Alaska left.''
But is there? The Caterpillars' tracks cut through the tundra remain visible for 100 years. Already there are only 40 wolves in Denali. And the pipeline cuts across the Arctic.
The Inupiat's way of life is altered forever. A native leader said: ''We can't eat money; we can't build a fire with it; it's the land that provides what we need. Without it we are nothing.''
In Anchorage the next day, I met with one of Alaska's leading state senators, a sensitive, intelligent, and highly principled man. I asked him about the future of the wilderness - up against mining, oil, timber, ''resources.'' In the course of explaining ''controlled development,'' he, too, said: ''There's a lot of Alaska left.''
An outsider, in love with the beauty of Alaska, might well feel that we can't afford to part with any of it.
The Mountain Travel trip described is the Alaska Wildlife Safari. The 17-day trip costs from $2,185 to $2,365, depending on the number of members. Further information about the trip can be obtained from Mountain Travel, 1398 Solano Avenue, Albany, Calif. 94706. Telephone (415) 527-8100.
Air North was our carrier to Katovik; this airline has a monopoly on a whole section of Arctic Alaska. Be prepared for delays caused by weather or inadequate equipment.
For information about the park, write Denali National Park and Preserve, PO Box 9, Denali National Park, Alaska 99755. For information about the area described south of Kaktovik, write Refuge Manager, Arctic National Wildlife Refuge, 101 12th Avenue, Box 20, Fairbanks, Alaska 99701.