The bus driver has slowed down so that we can gape.
His cry alerting the passengers is one we hear often on the Alaska Highway, and not just for bear sighting.
Dall sheep, standing out in brilliant white against rocky mountain slopes.
Moose, elk, grizzlies in the distance.
A lone wolf slouching across our path.
Caribou sighting becomes old hat.
The highway is exploding with life and color and the salmon are running.
Once, as our Greyhound bus skirts a river, we see a bald eagle swoop down on the water, talons outstretched.
For a brief second it rises with a huge salmon in its vice-like grip.
The salmon's struggle and its sheer weight drags the eagle into the river.
Hunter and prey actually become submerged.
As suddenly as it had vanished, the eagle resurfaces, thoroughly doused but grimly hanging on to its catch.
Barely able to flap its wings, it fights its way out of the water, never releasing its hold on the salmon.
The driver tells us he had seen similar encounters - but then anything is possible along this road of wilderness mystique.
The Alaska Highway's length alone is daunting - 2,378 kilometers.
It is a picture postcard of spectacular scenery.
As the road moves north and west, the landscape changes from sprawling grainfields to a more rugged mountainous land, filled with white-capped rivers, turquoise lakes and ice-blue glaciers.
Classic northern forests are full of wildlife and wildflowers.
The land is also a mosaic of people who run lodges, fly bush planes, man gas rigs and drive trucks.
Travelers meet old-timers like Dean (Old Griz) Elston, who teaches "cheechakos" (greenhorns) how to pan for gold at Kluane Wilderness Village in the Yukon.
Old Griz himself is a "sourdough", the affectionate name giving to old-timers.
There is only one way for a cheechako to become a sourdough: watch the river freeze in the fall and stay to see the ice brake into grinding pieces in the spring.
Old Griz, one of the bulldozer operators who helped build the Alaska Highway in 1942, has some tall tales to tell.
The road was finished in an astonishing eight months, probably the greatest engineering feat since the building of the Panama Canal.
The project was a wartime venture.
The highway linked Alaska to the rest of the United States and could have served as a way to move troops if Japan had attacked the territory.
It also served as an overland route to supply the chain of gravel airstrips across northern Canada and Alaska that provided emergency landing facilities for the 8,000 warplanes ferried to the Soviet Union.
At the peak of its construction, about 11,000 US soldiers and 7,500 civilians with 11,000 pieces of equipment built the road at a frenetic pace of 13 kilometers a day, sometimes in temperatures of minus 40 degrees Celsius.
It was a hard life.
The men had to build 133 bridges and 8,000 culverts.
Machinery snapped, ice jams rammed pilings, flash floods ripped out bridges after heavy rainfall or rapid glacial melts, bottomless muskeg swallowed trucks and bulldozers.
Slowly, a rough, rutted track took shape, forging a highway over marshes and bogs, through forests, over five mountains and through river canyons.
The road-builders were plagued by huge mosquitoes and blackflies.
A popular story is that they built two airfields at Whitehorse: one for aircraft, the other for mosquitoes.
One old-timer swears that on one occasion someone mistook a mosquito for a float plane and tried to refuel it.
The Alaska Highway is still a wilderness road today, but many of the curves have been straightened and the two-lane highway is paved.
There is occasional evidence of human habitation - hamlets tucked away among the trees, a cluster of log cabins, a roadside cafe or motel - but for the most part it's a pretty lonely road.
Every year about 200,000 travel its length.
We chose the easy way - we "rode the dog", and let the Greyhound Bus drivers do the work.
The journey started at Dawson Creek in northern British Columbia, Canada, where the famous Mile Zero sign post is a magnet for tourists.
The bus pointed its nose down the long, narrow ribbon of highway and over the first 900 kilometers threaded its way through serene, undulating prairies.
After Fort Nelson came the Rockies.
The Highway passes through two provincial parks and through rustic communities like Summit Lake and Toad River.
Then it winds through the valley of the Liard River and along an old Indian and fur-trading trail.
When the Greyhound approached Watson Lake, we were in the Yukon, where the sun shines for at least 20 hours a day for much of the summer.
The bus stopped within yards of the Sign Post Forest.
Here, in 1942, a homesick soldier, working on the highway erected a sign pointing to his home town in Danville, Illinois.
Over the years, others followed his lead and today there are 20,000 signs, of every shape and size, most of them "stolen" from their towns and cities.
After leaving Watson Lake, the Greyhound climbed beside the scenic Rancherie River, passing through the wide valleys of the Yukon mountain ranges to Whitehorse, Capital of the Yukon.
Whitehorse's buildings are a happy mix of pioneer spirit and urban sophistication.
Log cabins share streets with modern office buildings.
It's also littered with the history of the great Klondike gold rush.
Whitehorse was one of the staging points for the 30,000 fortune-hunters who poured into the Dawson City area at the end of the 19th century.
The sternwheeler SS Klondike now rests on the bank of the Yukon River.
It and its sister ships were once the main lifeline linking Whitehorse and Dawson City.
The Yukon takes its name from an Indian word, "Yuchoo", which means "the greatest river".
It's an appropriate name for a river that flows through what is still a vast and unspoiled frontier, a latticework of wilderness rivers, lofty mountains and glaciers.
Much of the Yukon is still unserved by road.
The only way in is to paddle, walk or fly in a float plane.
There are just 30,000 people scattered over its 483,000 square kilometers, but it is home also to more than 200,000 caribou, 50,000 moose, 25,000 thinhorn and stone sheep, 10,000 black bears, 500 wolves and 254 species of birds.
Beyond Whitehorse, the highway skirts the 22,000 square-kilometer Kluane National Park.
Kluane is an Indian name for "a place of fishing", and its lakes and rivers teem with salmon and trout.
At its heart lies a sea of ice - the largest non-polar icefields in the world - from which the massive glaciers flow through the valleys.
From here the Alaska Highway makes a relatively flat run to Fairbanks.
Our bus made a stop at North Pole, a small town about 20 kilometers before Fairbanks.
This is where the US Post Office delivers all the mail it gets for Santa Claus.
It's here that Santa's elves scramble to meet every Christmas wish - a place that makes dreams come true.
Dreams like ours - to drive the Alaska Highway.