Cormac McCarthy's novel "All the Pretty Horses" has always seemed to me the weakest, most artificially constructed of his West Texas trilogy, but the power of his language is so great that we read it for the way he helps us open ourselves up to a physical world grander than any human -- particularly his protagonists -- could ever own. His people take days on horseback, weeks even, to cross mountain ranges and deserts that appear to have been built in some heavenly workshop of infinite space. You grab an atlas and try to follow their routes on a map as the land expands beyond their ability to comprehend it.

In making the novel into a film, director Billy Bob Thornton and screenwriter Ted Tally ("The Silence of the Lambs") have chosen to focus on the story and not the setting. It's understandable; would we sit still for three weeks of inarticulate young cowboys exploring the dry country of north Mexico? But that's where the true power of McCarthy's novel lies, and not in the trite, adolescent love affair and its consequences that the film, and the novel, give us.

The year is 1949. Young John Grady Cole (Matt Damon) and his pal Lacey Rawlins (Henry Thomas) take off for Mexico from somewhere near San Angelo, after Cole's mother has sold off the family ranch and left him nowhere to stay. They pick up a runaway named Jimmy Blevins (Lucas Black), a wild child on horseback, and the three of them cross the Rio Grande, the demarcation line between boyhood and adulthood, where now they must choose their own fates and futures. Cole and Rawlins find work as ranch hands on a classic Mexican spread, owned by a wealthy man who flies his own plane each week to Mexico City. His daughter Alejandra (Penélope Cruz, and both Damon and Cruz are getting a bit long in the tooth to play teenagers in love, or even young twenty-somethings) catches John Grady Cole's eye and vice versa, and even though -- fill in the blanks -- she is not allowed to do this, her reputation is all, he is just a simple ranch hand and not even Mexican at that, etc., -- they do in fact find a way to spend their nights together in the stable.

But of course the family finds out, and aunt Alfonsa (Miriam Colon in a delicious part with the single best line in the film: "In the end, Mr. Cole, we are all cured of our sentiments. Those whom life does not cure, death will.") tries, unsuccessfully, to make John Grady see the light. Both young men are arrested and imprisoned (the police captain is played by Julio Oscar Mechoso, an actor with the most compelling presence in the film), and the rest of the movie follows Cole as he returns to be with Alejandra again, and its consequences for both of them.

Thornton has chosen his shots well, staged the action with power, and hasn't overwhelmed it all with flashy camerawork or editing. He has a marvelous feel for composition, for conveying the nature of the land through which the film moves, and he gives his actors breathing room. The sequences in the prison are particularly effective, shot and lit by Barry Markowitz and edited by Sally Menke. Nevertheless, the triteness of the story keeps pulling us back; we can't give ourselves to it because it's just too shallow.

McCarthy's other novels, bloody and brutal as they are, rely for their power, even more than this one, on what has to be called the beauty of his language, his ability to evoke a scene, an image, a haunting memory that cannot be erased even years later. Though I would love to see them filmed, we're probably better off that no one will try.