As police chief of this idyllic Shenandoah Valley town, Marshall A. Robinson typically spends his days checking to make sure residents have locked their doors, stopping in on seniors who live alone, waving and honking at friends every half-block. But in the past week, he has added a new stop to his rounds: a construction site where he believes members of one of Virginia's most violent gangs are working.

"We're used to our little vandalism, larcenies, smoking a little pot," said Robinson, who grew up in this town of 4,000 that sits beside the Massanutten Mountains, at the northern tip of the Shenandoah Valley. "But now we're into this whole MS-13 thing," he said, using the abbreviation for Mara Salvatrucha, a violent gang whose members he suspects are mixing among day laborers in Strasburg.

After years of watching news reports about violent gangs in the Washington suburbs -- or "over the mountain," as people here call places like Manassas and Alexandria -- residents of the rural belt that parallels Shenandoah National Park are finding that gang members in the nation's capital are doing what many others are doing: migrating farther out in search of a better quality of life.

Their arrival has been marked in subtle ways: "MS-13" spray-painted on the side of a red barn, a game warden harassed by gang members while checking fishing licenses, gang tattoos showing up at county fairs. The ugliest calling card, the one that transformed law enforcement dialogue on the topic, was found in the most beautiful of spots. At a particularly lush curve of the Shenandoah River, in a vast valley called Meem's Bottom, the body of Brenda Paz, 18 years old and four months pregnant, was found knifed and floating last summer. Law enforcement sources said Paz had been providing information in a half-dozen investigations across the country, including a homicide case in Alexandria allegedly involving members of MS-13.

On May 20, federal and local law enforcement officials held a joint news conference 80 miles away in Fairfax County to warn about the spread of gang violence through exurbia and into the rural Shenandoah Valley. They pledged $500,000 in additional funds for a problem that recently escalated with a machete attack on a Fairfax youth and the shooting death of a Herndon teenager, one of at least seven slayings in Northern Virginia linked to MS-13 since 2000.

Law enforcement officials in the Shenandoah Valley say they believe sprawl from the inner suburbs is the main reason for an appearance in the last year or two of violent and largely Latino street gangs. But there are other likely reasons, including a well-established community of Latino immigrants in which to blend, including thousands of Mexicans and Salvadorans drawn here for jobs in the poultry, plastics and construction industries.

Some investigators fear that gangs want a piece of the region's large drug market, a trade that centers on methamphetamine -- or "meth" -- from Mexico. Others believe gang members are just young Latinos who see gangs as something socially binding in a segregated place.

At this point, law enforcement officials acknowledge that they do not know precisely what they are dealing with. Only since Paz's slaying has attention turned to the topic, and information-gathering is so new that basic questions are unanswered: How big is this gang population? Are the members mostly teenagers or adults? And most, importantly, what motivates them?

"We can't do something until they do something, so for now we are going to take pictures; we are going to identify them," Robinson said. "For now, we're just waiting."

Todd Gilbert, assistant commonwealth's attorney for Shenandoah County, believes that gang members live in the Shenandoah region but that they do not have any real infrastructure -- yet. "Our worst-case scenario would be to get competing gangs. I can almost get a palpable sense it may be coming."

A few months after the Paz slaying, gang graffiti popped up in a dozen places in Woodstock, the second-largest community in Shenandoah County, with 3,500 people. Law enforcement officials began sharing more information with one another, holding training sessions with their counterparts in the Washington suburbs and becoming more aggressive about gathering intelligence.

Although there is disagreement about how well entrenched gang members are in the Shenandoah Valley and what their goals are, law enforcement officials agree that the counties along Interstate 81 -- Frederick, Shenandoah and Rockingham -- have experienced an increase in gang activity. Authorities have inadvertently crossed paths with gang members, either by staking out public events, such as fairs, or by running across them in criminal cases such as domestic disputes or shoplifting.

Only one person in the northern Shenandoah Valley has been charged specifically with being involved in MS-13 or Surenos (SUR-13), Gilbert said: Juan Jose Valencia Ramirez, 19, who police said spray-painted a gang tag on a dumpster in Woodstock this year. He was charged with damaging property and with doing so as part of a criminal gang. He agreed to a plea agreement that convicted him of property damage but gave him a year-long sentence with six months suspended -- much longer than the typical penalty without the gang association, he said.

Capt. Garlan Gochenour, commander of a regional task force focused on drugs and gangs, said his group has handled dozens of cases in the past year involving gang members -- even if the people were not charged with being in a gang.

To whatever degree drugs are a factor, the Shenandoah Valley is the place to be, Gochenour said. Shenandoah County is one of the country's meth hubs, and aspiring drug dealers find it a more pleasant business climate, with less violence involved in staking out turf than in the city. According to Gochenour, methamphetamine was selling for about $32,000 a pound in Shenandoah County in the late 1990s but is now about $4,000 a pound as the supply has grown.

The region had its biggest crackdown on MS-13 and SUR-13 early this month, when authorities raided 10 apartments, trailers and houses in Woodstock in the middle of the night and arrested 47 people, including 17 on immigration violations and 30 on drug-related charges. Although no one has been charged with gang-related crimes, officials said they believe many are gang members. They also said they learned more about the gang infrastructure during the investigation, which was extended for months when officials realized the gang connections.

Gangs are not new to the region. There have long been biker gangs, and last year, Shenandoah County was at the center of a six-state investigation of the Warlocks biker gang that led to 34 arrests, mostly on drug and weapons charges. In the mid-1990s, authorities in Winchester cracked down on a street gang that was mostly involved in petty crime. The difference with gangs such as MS-13 and SUR-13 is their record of brutality, officials say.

"Usually, gang violence is associated with drugs, money and violence. With these people, it seems to just be about violence," said Capt. Allen Sibert, who works on drug and gang cases in Warren County.

Selling these ideas won't be easy in cheery Shenandoah Valley, where road signs direct travelers to caverns, fishing holes and covered bridges and where crime is low.

Rick Lambert, whose family owns the red barn that was tagged six months ago, smiled in the most undisturbed manner when asked how he felt about being targeted by an MS-13 member.

"A week later, we got an apology letter," Lambert said of the 17-year-old, who offered to pay for the damage. "But we said we were tearing it down anyway."

Lambert surmised that the barn was targeted because Lambert's Moving and Storage is "on the outskirts of town. Nobody bothers us."

Lambert's casual attitude was mirrored even at Valley Vista apartments, where six apartments were raided a few weeks ago and where officials said MS-13 members live.

"The only problem we have is sometimes they drink in the parking lot and play loud music," said Maria Duque, 16, who translated from Spanish the opinion of her father, Virgilio, 48, about young men in the complex. The family moved to Woodstock from Mexico five years ago, she said, and has never seen any evidence of gangs, she said.

Then Maria Duque and her parents got into their van, which was parked in front of a clean red brick wall. Just a few months ago, before it was cleaned, the wall was scrawled with black writing: "MS-13."

Gang graffiti appears next to the Meem's Bottom bridge in Shenandoah County, Va., where police also have spotted people with gang tattoos.Shenandoah County Sheriff Tim Carter looks over photographs of gang graffiti in his Woodstock office. Authorities say the drug trade and a desire for a better lifestyle have drawn gang members to the area from Northern Virginia.At the Valley Vista apartments in Woodstock, MS-13 graffiti was crossed out and replaced with SUR-13 graffiti. The tags have since been removed.Brenda Paz, 18, was found slain on the Shenandoah River last year. Paz had been providing information in gang cases, including one in Alexandria.