Local legend has it that this thirsty pocket of arid northeast Mexico, 125 miles from the U.S. border, once was home to the most vile Indian witches.
Following the arrival of the Spaniards, the witches' spirits were locked in a petaca , or trunk, and buried during an exorcism, giving the town of 2,000 people its name.
Crosses were put up at La Petaca's four corners to ward off evil. They remain. So does the area's reputation as a caldron where witches can cook up their magic.
"I can't believe I'm here," says a young woman named Sonia after waiting six hours with dozens of others for a "consultation" with Maria Cepeda, a famous witch.
Sonia says she needed help because her husband left her with a year-old son and a baby on the way. "Sometimes you get so desperate you'll try anything," she says.
The term witch is generic in Mexico, covering a wide range of people who serve as doctor-counselor-confessor, treating illnesses and personal problems with a mix of religion, herbal medicine and folk psychiatry.
Witches are sought to help solve problems ranging from colds and migraine headaches to getting a raise or finding a husband. Many witches claim darker powers that can harm enemies.
Almost every neighborhood market has its share of herbarios , stands that sell tools of the witchcraft trade, from crowns of garlic, plastic skulls and black candles to magic powders used to restore lost love, rein in philandering spouses or wreak havoc on a romantic rival.
The central and southern states of Veracruz, Oaxaca, Morelos and Michoacan also are famous for witches.
Although they may claim to be skeptical, many Mexicans, from presidents to peons, have had some contact with witches and their practices.
"Folk healers can be found in just about any Mexican community," says William Murray, who teaches medical anthropology at the University of Monterrey. "It has a great deal of psychosocial value."
Witches are referred to as such by everyone but themselves. They usually prefer terms such as curanderos (healers), hechiceros (sorcerers), mentalistas (mind readers), medios (mediums) and videntes (clairvoyants).
Patients tend to come from the lower and middle classes, but witches have their richer followers as well.
" Curanderismo has enjoyed an upswing in recent years because of Mexico's troubled economic situation," Murray says.
Even President Carlos Salinas de Gortari submitted to a ritual limpia , or cleansing, during a recent visit to Morelos. This practice involves passing black chickens, herbs, rocks or eggs over a person's body to draw out illness and evil and bring good luck.
Many Mexicans consider illness not so much a physical problem as an emotional or spiritual one, Murray says. A sluggish or nervous person may blame his condition on mal de ojo (evil eye) or susto (scare).
These maladies are treated with herbs that have medicinal properties known since pre-Columbian time and rituals such as limpias that at least help a patient believe he will get better.
Murray says the university teaches its medical students to respect these practices so they can treat the community more efficiently.
"Patients use these terms to explain the way they are feeling," he says. "It is part of the cultural vocabulary of illness, and students must be taught how to recognize it."
Witchcraft in Mexico dates to the Aztecs. With the arrival of the Spaniards, witches began mixing it with European traditions, such as Catholicism, to the dismay of the Roman Catholic Church.
"Most curanderos are charlatans," says Father Raul Rodriguez of Monterrey's Church of the Divine Providence, who has studied different sects and folk Catholicism.
"A desperate person will try anything. It's pure superstition, but a lot of people follow it."
Still, witchcraft in its various forms is a part of daily life in Mexico.
On a busy downtown Monterrey street, vendors hawk herbs by the pound, along with rows of colored oils guaranteed to bring luck and love, soaps to grow hair and pills to cure infertility.
At the nearby Colonia Market, a young girl sits behind the counter of a shop filled with books on magic, framed pictures of saints, candles, perfumes and charms.
A customer complaining of insomnia is given two bags of herbs to mix as a tea before bedtime. Another whose boss is bothering her is told to light a candle and repeat a prayer for nine nights to "get rid of him."
"Will it really work?" the client asks.
"Only if you have faith," replies the salesgirl.
Avelina Reyes de Guerrero agrees. The 71-year-old woman has been providing trabajos , or works, for 30 years from a room behind her small convenience store in Linares, near La Petaca.
"First you need faith in God, whatever God that may be. Religion doesn't matter," she says. "You also need confidence in the person attending you."
She sees about 15 people a day from all over Mexico and some from the United States.
Witches rarely advertise, preferring word of mouth. Prices tend to vary. Reyes, for example, takes whatever a patient can give.
"This is not a business," she says. "If someone is asking for economic help, I can't very well charge them, can I?"
Most witches, including Reyes, willingly send patients to medical doctors if they believe the problem is beyond their capabilities.
She considers herself a good Catholic and dismisses the church's concerns.
"Some of the biggest cures are exorcisms, and only priests do those," she says.
Reyes says her family stopped talking to her when she began training with a clairvoyant. "Now, I'm the first person they come to," she says. Now she even has a niece as an apprentice.
Cepeda, in her 70s, gives consultations every Friday beginning at 5 a.m. from her ranch in La Petaca.
Although the legend lives on, she is only one of two witches left there.
Sitting behind an old desk, she receives clients in a room filled with statues of the Virgin of Guadalupe and Jesus Christ, pictures of Pope John Paul II and lighted candles.
When Sonia finally got in to see her, Cepeda asked for her husband's birth date, did some rapid calculation, and announced that there was nothing she could do.
A true witch, practitioners say, would never pretend to help unless he or she actually could.
But that was little comfort to Sonia.
"I'm worse off now than I was before," she said disconsolately.