It's a classic story, almost a trite one. The son of a dour Scottish immigrant father and complaisant mother rebels against domestic puritanism, indulges in errant behavior. What distinguishes John Muir's course from thousands of others' in mid-19th-century America is the substance of his binges -- not wine or women but wilderness. Muir rejected his father's fundamentalist scoldings because they epitomized the Calvinist notion that "one sure way to recognize a sinner was that he delighted in looking at natural objects, for such objects were fated for eventual destruction, and so delight in them was an offense against the Lord."

Muir certainly delighted in nature, but his ardor went further. He longed to understand the workings of natural systems. His sojourns in the Sierra Nevada led him to the bold conclusion, which he maintained successfully in the face of scoffing by professional geologists, that Yosemite Valley is the product not of violent upheavals and subsidences (the orthodox view at the time) but of glaciation.

In Frederick Turner's view, the crucial decision of Muir's life was whether to take the advice of his mentor Emerson and enter the public arena or remain a traveling hermit. He was well suited to solitude: He once rode out a storm at the top of a 100-foot Douglas fir, which he had climbed so that he could experience the motion of trees. He felt that, unlike the rest of his practical family, he was useless. He seemed preordained for the self-contained practice of mountaineering. "Muir began to slide up that mountain," a friend wrote of his climbing style. "I had been with mountain climbers before, but never one like him."

Yet however much he resisted his father's lectures, Scottish industriousness had gotten hold of Muir. His early writings put him in demand as an author and speaker, and he realized he would have to come down from the mountains. He would make it his life's work to treat a deplorable American condition: to be, in Turner's words, "in daily contact with magnificent landscape and not be touched by it or even mildly interested in its most spectacular features."

Among his crowning achievements were the successful campaign to preserve Yosemite as a national park and the founding of the Sierra Club. He lost another great fight: the controversy over whether the city of San Francisco should be allowed to dam the Tuolumne River in Yosemite's Hetch Hetchy Valley for its drinking water supply. But in a sense he triumphed even there: His genius for publicity kept the violation of Yosemite from being a precedent, and the national parks have been kept virtually inviolate ever since.

Besides being an activist, Muir was an author and philosopher. Though his style occasionally bogs down in quaintness, he is still quite readable, especially in "The Yosemite" and "Travels in Alaska."

One of his philosophical preoccupations was with reconciling himself to death after having shed his Christian beliefs. He found the required solace in nature, where death and life can be found in "beautiful blendings and communions" and "all is divine harmony." Moving farther afield from his father's credo, he wrote in his journal that his days "spent alone in the depths of the wilderness have shown me that immortal life beyond the grave is not essential to perfect happiness, for these diverse days were so complete there was no sense of time in them, they had no definite beginning or ending, and formed a kind of terrestrial immortality."

The great strength of this new biography of Muir is that it allows the reader to follow his progression from a young vagabond to the crony of presidents. (Turner describes Muir and Teddy Roosevelt camping out in Yosemite, utterly alone together in "creative truancy.") To help convey Muir's development -- and particularly his invention of a new American career, that of conservationist -- Turner frequently ascribes to him "perceptions for which there is no precise proof" in the record. For instance, though Muir often noted the memory-stirring powers of the sea air at his Scottish boyhood home, Turner is persuaded that the nearby hills exerted a stronger influence on him.

In the wrong hands, such must-have-felts can produce unfounded figments, but Turner's projections seem solid. Much of his authority to make them derives from the profound rapport between himself and Muir that is evident on almost every page.

Turner, who has previously written on the West, wilderness and jazz, is also a phrase maker. I particularly like his description of Muir's death (in 1914, at age 76): "When he was alone for a moment, he went. At the end there was no great wrestling against the fading of the light, but rather a simple saunter on into the next season." Indeed, "Rediscovering America" is a biography as shapely as its subject's life and death.