Bigleaf maples at Cache National Forest

A drive through its canyon or mountain wilderness reveals the true colors of the Pacific Northwest.

By Brian Doyle

Because trees don't move much—just swaying from the waist in their windy aerobics classes—we forget that they are remarkably sensitive creatures, able to gauge the slightest gradations in light, heat, and available water.

They eat sunlight, drink rain by the ton, know a lot more about soil chemistry than we do, and house animals ranging in size from bacteria to black bears. We owe them gratitude for any number of reasons—wood, shade, windbreaks, holding hills together, cleaning the planet's air—but the most visible delight they provide may be the international art show they put on every fall, when tree leaves in the Northern Hemisphere suddenly have the brilliant color seizures that have riveted human beings for thousands of years.

But why do leaves burst into color, exactly? It's a sort of magic trick, a sleight-of-leaf maneuver in which the tree, sensing impending autumn, yanks the green from the leaf, thereby exposing the leaf's true color. The "real" colors of deciduous trees—trees like oaks and maples that flop broad leaves out in spring and drop them hurriedly in winter—are the ones you see in autumn. Spring and summer are one long green disguise, a cacophony of chlorophyll. Technically, the matter of leaf color is a tad more complex: reduced production of chlorophyll affects a leaf's light-absorption facility, revealing its basic carotenoids, the pigments that absorb light maximally between certain wavelenths, which means we see them as red, orange, yellow—but you knew that.

A leaf changing color is essentially a business decision by the tree, which reads the market (a slight decrease in daily light, temperature, and water in the soil, as summer ends) and lets a segment of the company go, to conserve resources. The tree shuts down chlorophyll production, which yields a brightly colored revelation of true inner-leaf nature—and then, along about Nov-ember, mass leaficide, as the tree cuts loose the light-factories that were going full blast all spring and summer. Down to the ground they go in their uncountable trillions, to become ceilings for the tiniest creatures of the woods, a building block for soil, and a hill of troubles for lovers of lawns.

Coniferous trees, like the Douglas fir that dominates the western slope of the Cascades, choose another path in cultivating light. They decide to play the percentages, as it were, throughout the year—to keep clothed in their slim needles, which are indeed leaves, and recruit what light they can find over the fall and winter. Firs and their cousins do produce new leaves in the spring, but these are extensions of the current crop, and act primarily as replacements for the needles that are lost to weather and disease. The coniferous trees are bears, cautious creatures with a long-term view; the deciduous trees are bulls, trying to make the most of the moment.

New England, with its wide spectrum of deciduous trees, looms in most minds as the epitome of autumnal brilliance. But the Pacific Northwest, in its mountain and canyon wildernesses, boasts stunning displays of aspen, cottonwood, maple, oak, alder, and birch.

In autumn, my favorite Oregon artery is the McKenzie River Highway. This serpentine path, mostly a two-lane road that loops and bends with one of Oregon's most beautiful (and unpolluted) rivers, runs from Eugene to the crest of the Cascade Mountains. A car heading east can cut through the mountains at 5,000-foot McKenzie Pass and drift down into the town of Sisters, through an eerie lunar landscape of ancient lava beds. From Eugene, where all the sundry pleasures of a college town are on exhibit—superb coffee, music shops, bookstores, a plethora of pizzerias—the McKenzie Highway winds west initially through a pastoral landscape of small farms and hazelnut orchards before aligning itself tightly with the river and entering a region of mammoth fir trees and towering hills—the foothills of the Cascade Range.

For all the quiet pleasures available along the McKenzie Highway—trout-fishing, gaping at the resident ospreys, trying to spot the enormous chinook salmon that return every fall to spawn, or gobbling blackberry pie—the simplest pleasure is savoring the river's endless beauties, especially in the fall. The McKenzie River Valley, being west of the Cascades and so catching some 80 inches of rain a year, is mostly coniferous—yew, cedar, hemlock, and fir. But there are deciduous species as well, and the sharp-eyed observer along the McKenzie will find maple, oak, cottonwood, alder, salal, madrone—and the brightest of Oregon's autumnal colors, the searing orange of vine maple. Ah, to be by an orange maple with a blackberry pie on a blue day . . .