However high the sun, the time of day is always twilight in Sally Mann land, a twilight that has the edgy wistfulness of a boring day at a vacation house, a twilight with a sense of stain, a shopworn twilight marked by poignancy, the itch of appetite and a feeling like being tired of being stoned.

Self-consciousness, the venial sin of our age, is the state of mind. Her pastures look like forgotten battlefields, her woods are full of ghosts, and roots rise from swamp water like tentacles of Chaos. Things have a suspended quality, the sense of "foregone conclusion" that William Hazlitt found in the 17th-century paintings of Poussin: "There is a significance, a consciousness . . . everything seems to have a distinct understanding with the artist; 'the very stones prate of their whereabout.' "

Mann's buildings look as if they were photographed only hours before they burned down. Pillars rise from plantation ruins with Lost Cause self-satisfaction. In Mann's scandalous 1992 photographs of her own naked, wounded, sexy, beautiful, tired and dirty children, there's corruption, but it's nothing more than a sort of moral twilight. One feels a slight shudder at the scent of evil, the Beast himself about to wake from a nap in the late afternoon woods.

It's a Southern thing, too. In an interview Mann once said: "Well, that's the thing about the South and Southerners. We are, as Shelby Foote said, 'sick from an old malady, incurable romanticism and misplaced chivalry. Too much Walter Scott and Dumas read too seriously. We are in love with the past, in love with death.' "

Decay, evil, timelessness, and the hoofprints of the Archfiend -- how alluring, and how daring for the beautiful mother of three beautiful children, wife of a Lexington, Va., lawyer, the daughter of a respected doctor, and resident for 53 years of 423 beautiful acres of family farm, a Hollins graduate, a woman of the South. Her photographs are gothic, morbid, erotic and fatalistic. No wonder she has fame and glamour despite her lack of attention from (and to) the institutional art establishment.

Now, in "What Remains," a big show at the Corcoran Gallery, more than 150 images, Mann's subject is death. The twilight deepens as she moves toward the most foregone conclusion of them all.

How beautiful these pictures can be -- the dark, doomed noons of the Antietam battlefield; the glow of fabric over the rotting torso of a screaming skull; the noble and ghost-vague faces of Mann's children, like something you glimpse while driving past the midnight site of a fatal accident; the classic figure study that happens to be modeled by a fat female corpse left to decay in the leaves at the University of Tennessee's forensic research center, and the spot on her land where an escaped prisoner shot himself to death while she watched from the house as the police closed in on him.

The show begins with a 30-by-40-inch picture of her beloved greyhound, Eva.

A leash rises straight from her neck, as taut as if she had been hanged, but her feet are on the ground. An aura of white erupts from her back, in the manner of evidence presented by a psychic. Lens flare? Chemical failure?

The next picture shows Eva's skin hanging from another vertical cord. After Eva died, Mann hired a taxidermist to remove it. Mann then buried Eva in a metal cage, so she could dig her up a year later and photograph the dirty, hairy joints, teeth, and worm-worked thigh bones that float over uncertain surfaces.

Dust to dust: Eva does not await her mistress in doggy heaven. Her only afterlife is biodegradability (formerly known as rot, just as wetlands were formerly known as swamps). In wall text, Mann quotes a 17th-century bishop, Jacques-Benigne Bossuet: "Nature . . . cannot for long allow us that scrap of matter she has lent . . . she claims it back for other works." Eva is pushing up daisies, as they say, no more and no less. This theme dominates the show.

Mann makes her time-out-of-mind pictures with a wet-collodion process introduced in 1851. She coats a glass plate with silver nitrate and inserts it in an 8-by-10 view camera. She has five minutes to take the picture before the coating dries. Many accidents can happen. Nineteenth-century photographers tried to avoid them. Mann welcomes them. She relishes the accidental flare over Eva's back, or the vaporous residue (fog and flames of Hades?) surrounding the strewn corpses in Tennessee, or the accidental white spots scattered like stars over the grass of the Antietam battlefield, or the chemical veils that leave her children's faces receding into oblivion.

The accidents say three things:

One, this picture is a work of art, not a document. Two, the pictures are moldering along with the bones and corpses. Three, and most sentimentally, spirits teem over the dead like sugar ants over spilled wine.

As usual, Mann sidles between the dramatic and the manipulative. She tempts us to superstition with her chemical stars much as she tempted us to thoughts of pedophilia in 1992's "Immediate Family," with the calculated eros of her prepubescent son and daughters.

The dog bones seem bodiless next to the heft of corpses rotting in woods and fields. Bloated flesh splits, fluid drains from buttocks, skin wizens, and after a while you have a hard time telling the corpses from the sticks and leaves. The antique glass plates make them look old, and the shock effects make them look new. Curiosity dances with disgust. Mann is good at ambiguities like this, at putting you between the rock and the hard place. She's a 21st-century modernist in her self-consciousness and lassitude, she's a lugubrious Victorian in the morbidity of her romanticism. You can never find a single viewpoint. She's not morbid, she's romantic; not romantic but gothic; not gothic but fatalistic; not fatalistic but realistic; not realistic but morbid . . .

The wall text next to the corpses is from Galway Kinnell, who argues against embalming and airtight caskets in favor of "the crawling of new life out of the old, which is what we have for eternity on earth." He would approve of the buzzard sizing up a body, or the flies walking on a woman of vast belly and breasts.

In an image of cloth-covered corpses scattered in a field, an apparent tear in the emulsion leaves the shape of the scythe carried by the Grim Reaper. Accident? Mawkishness? Irony? Death supplies enough irony for life without tarting it up with a cartoon scythe.

Mann has a way of rubbing your nose in ghastliness, be it sexual or mortal. She's a poet, and like a lot of poets she's proud of her fascination with death. She reminds me of Philip Larkin, England's great poet of the later 20th century, being too clever by half in saying of death:

It's only oblivion, true:

We had it before, but then

it was going to end. . . .

Next time you can't pretend

There'll be anything else.

She uses our own squeamishness as her motive and material. She's a daredevil, shaming her audience by confronting what they've shunned. So are lots of photographers, particularly photojournalists who take on the vocation of reporting slaughter, squalor and apocalypse. But Mann reports on nothing, she creates everything. She's not a professional bystander, she's the main event. She doesn't record, she creates. Then she exhibits. She may share a taste for squalor with journalists of all sorts, but she's not a voyeur, she's an exhibitionist.

She casts a cool eye on life and death, an eye she may have inherited from her father, a doctor, an atheist and an eccentric. She writes: "Not for him the euphemisms of death -- it was a dead body, not 'remains,' nobody 'passed,' there was no 'eternal rest.' People died and that was it." Her aesthetics may be his, too. She writes that he "jokingly claimed that there were three avenues for artistic expression: Sex, Death and Whimsy." Can we attribute the emulsion scythe to whimsy?

Let's hope so. The show is so powerful you want to love it, particularly when you see the bedrock compositions of the Antietam battlefield photographs, which are introduced with lines from Whitman about the fallen soldiers of Sept. 17, 1862:

And you streams, absorb them well, taking their dear blood . . .

And all you essences of soil and growth.

Dark, dark, dark -- Antietam was fought on a fine late-summer day, but Mann has chosen to portray the battlefield in a twilight of her own creation. Shadows float beneath noon trees, but you can hardly see them for all the gloom of dark skies over darker fields. Chemical fairy lights glimmer over the battleground, the emulsion turns to vapor, flames seem to dance over the cornfield that was cut to the ground once by bullets. A horizon line, a blurred fringe of grasses, some trees of antique demeanor, and that's all Mann needs for an authoritative composition with a self-defining wholeness, pictures that are right because they're right.

There's something true and inevitable rattling around in this show's bones, fields, rot and memory, a sense of release from time, and of the thorny indifference of the physical world. You sense that you share a truth with her. She provokes the sort of epiphany that in turn provokes a sense of beauty. Still, you're uneasy. In the words of an art dealer I know, "You keep feeling the need to explain her work."

The show takes its title from the final section, "What Remains." Once more she enlists her beautiful children -- they play full-lipped ghosts in extreme close-up, often with eyes closed. Sometimes there's hardly anything there to remain. The curve of a lip or the glare of an eye can make you ache with pleasure, but the twilight never lifts, and the kids seem to be receding into time or memory. They seem to question their own reality, in the manner of Death itself questioning the reality of us all.