The spring air in the small, sand-dusted town has a soft haze to it, and clumps of green-gray sagebrush rustle in the breeze. Bluffdale sits in a bowl-shaped valley in the shadow of Utah's Wasatch Range to the east and the Oquirrh Mountains to the west. It's the heart of Mormon country, where religious pioneers first arrived more than 160 years ago. They came to escape the rest of the world, to understand the mysterious words sent down from their god as revealed on buried golden plates, and to practice what has become known as "the principle," marriage to multiple wives.

Today Bluffdale is home to one of the nation's largest sects of polygamists, the Apostolic United Brethren, with upwards of 9,000 members. The brethren's complex includes a chapel, a school, a sports field, and an archive. Membership has doubled since 1978—and the number of plural marriages has tripled—so the sect has recently been looking for ways to purchase more land and expand throughout the town.

But new pioneers have quietly begun moving into the area, secretive outsiders who say little and keep to themselves. Like the pious polygamists, they are focused on deciphering cryptic messages that only they have the power to understand. Just off Beef Hollow Road, less than a mile from brethren headquarters, thousands of hard-hatted construction workers in sweat-soaked T-shirts are laying the groundwork for the newcomers' own temple and archive, a massive complex so large that it necessitated expanding the town's boundaries. Once built, it will be more than five times the size of the US Capitol.

Rather than Bibles, prophets, and worshippers, this temple will be filled with servers, computer intelligence experts, and armed guards. And instead of listening for words flowing down from heaven, these newcomers will be secretly capturing, storing, and analyzing vast quantities of words and images hurtling through the world's telecommunications networks. In the little town of Bluffdale, Big Love and Big Brother have become uneasy neighbors.

Under construction by contractors with top-secret clearances, the blandly named Utah Data Center is being built for the National Security Agency. A project of immense secrecy, it is the final piece in a complex puzzle assembled over the past decade. Its purpose: to intercept, decipher, analyze, and store vast swaths of the world's communications as they zap down from satellites and zip through the underground and undersea cables of international, foreign, and domestic networks. The heavily fortified $2 billion center should be up and running in September 2013. Flowing through its servers and routers and stored in near-bottomless databases will be all forms of communication, including the complete contents of private emails, cell phone calls, and Google searches, as well as all sorts of personal data trails—parking receipts, travel itineraries, bookstore purchases, and other digital "pocket litter." It is, in some measure, the realization of the "total information awareness" program created during the first term of the Bush administration—an effort that was killed by Congress in 2003 after it caused an outcry over its potential for invading Americans' privacy.

But "this is more than just a data center," says one senior intelligence official who until recently was involved with the program. The mammoth Bluffdale center will have another important and far more secret role that until now has gone unrevealed. It is also critical, he says, for breaking codes. And code-breaking is crucial, because much of the data that the center will handle—financial information, stock transactions, business deals, foreign military and diplomatic secrets, legal documents, confidential personal communications—will be heavily encrypted. According to another top official also involved with the program, the NSA made an enormous breakthrough several years ago in its ability to cryptanalyze, or break, unfathomably complex encryption systems employed by not only governments around the world but also many average computer users in the US. The upshot, according to this official: "Everybody's a target; everybody with communication is a target."

For the NSA, overflowing with tens of billions of dollars in post-9/11 budget awards, the cryptanalysis breakthrough came at a time of explosive growth, in size as well as in power. Established as an arm of the Department of Defense following Pearl Harbor, with the primary purpose of preventing another surprise assault, the NSA suffered a series of humiliations in the post-Cold War years. Caught offguard by an escalating series of terrorist attacks—the first World Trade Center bombing, the blowing up of US embassies in East Africa, the attack on the USS Cole in Yemen, and finally the devastation of 9/11—some began questioning the agency's very reason for being. In response, the NSA has quietly been reborn. And while there is little indication that its actual effectiveness has improved—after all, despite numerous pieces of evidence and intelligence-gathering opportunities, it missed the near-disastrous attempted attacks by the underwear bomber on a flight to Detroit in 2009 and by the car bomber in Times Square in 2010—there is no doubt that it has transformed itself into the largest, most covert, and potentially most intrusive intelligence agency ever created.

In the process—and for the first time since Watergate and the other scandals of the Nixon administration—the NSA has turned its surveillance apparatus on the US and its citizens. It has established listening posts throughout the nation to collect and sift through billions of email messages and phone calls, whether they originate within the country or overseas. It has created a supercomputer of almost unimaginable speed to look for patterns and unscramble codes. Finally, the agency has begun building a place to store all the trillions of words and thoughts and whispers captured in its electronic net. And, of course, it's all being done in secret. To those on the inside, the old adage that NSA stands for Never Say Anything applies more than ever.

A swath of freezing fog blanketed Salt Lake City on the morning of January 6, 2011, mixing with a weeklong coating of heavy gray smog. Red air alerts, warning people to stay indoors unless absolutely necessary, had become almost daily occurrences, and the temperature was in the bone-chilling twenties. "What I smell and taste is like coal smoke," complained one local blogger that day. At the city's international airport, many inbound flights were delayed or diverted while outbound regional jets were grounded. But among those making it through the icy mist was a figure whose gray suit and tie made him almost disappear into the background. He was tall and thin, with the physique of an aging basketball player and dark caterpillar eyebrows beneath a shock of matching hair. Accompanied by a retinue of bodyguards, the man was NSA deputy director Chris Inglis, the agency's highest-ranking civilian and the person who ran its worldwide day-to-day operations.

A short time later, Inglis arrived in Bluffdale at the site of the future data center, a flat, unpaved runway on a little-used part of Camp Williams, a National Guard training site. There, in a white tent set up for the occasion, Inglis joined Harvey Davis, the agency's associate director for installations and logistics, and Utah senator Orrin Hatch, along with a few generals and politicians in a surreal ceremony. Standing in an odd wooden sandbox and holding gold-painted shovels, they made awkward jabs at the sand and thus officially broke ground on what the local media had simply dubbed "the spy center." Hoping for some details on what was about to be built, reporters turned to one of the invited guests, Lane Beattie of the Salt Lake Chamber of Commerce. Did he have any idea of the purpose behind the new facility in his backyard? "Absolutely not," he said with a self-conscious half laugh. "Nor do I want them spying on me."

For his part, Inglis simply engaged in a bit of double-talk, emphasizing the least threatening aspect of the center: "It's a state-of-the-art facility designed to support the intelligence community in its mission to, in turn, enable and protect the nation's cybersecurity." While cybersecurity will certainly be among the areas focused on in Bluffdale, what is collected, how it's collected, and what is done with the material are far more important issues. Battling hackers makes for a nice cover—it's easy to explain, and who could be against it? Then the reporters turned to Hatch, who proudly described the center as "a great tribute to Utah," then added, "I can't tell you a lot about what they're going to be doing, because it's highly classified."

And then there was this anomaly: Although this was supposedly the official ground-breaking for the nation's largest and most expensive cybersecurity project, no one from the Department of Homeland Security, the agency responsible for protecting civilian networks from cyberattack, spoke from the lectern. In fact, the official who'd originally introduced the data center, at a press conference in Salt Lake City in October 2009, had nothing to do with cybersecurity. It was Glenn A. Gaffney, deputy director of national intelligence for collection, a man who had spent almost his entire career at the CIA. As head of collection for the intelligence community, he managed the country's human and electronic spies.

Within days, the tent and sandbox and gold shovels would be gone and Inglis and the generals would be replaced by some 10,000 construction workers. "We've been asked not to talk about the project," Rob Moore, president of Big-D Construction, one of the three major contractors working on the project, told a local reporter. The plans for the center show an extensive security system: an elaborate $10 million antiterrorism protection program, including a fence designed to stop a 15,000-pound vehicle traveling 50 miles per hour, closed-circuit cameras, a biometric identification system, a vehicle inspection facility, and a visitor-control center.

Inside, the facility will consist of four 25,000-square-foot halls filled with servers, complete with raised floor space for cables and storage. In addition, there will be more than 900,000 square feet for technical support and administration. The entire site will be self-sustaining, with fuel tanks large enough to power the backup generators for three days in an emergency, water storage with the capability of pumping 1.7 million gallons of liquid per day, as well as a sewage system and massive air-conditioning system to keep all those servers cool. Electricity will come from the center's own substation built by Rocky Mountain Power to satisfy the 65-megawatt power demand. Such a mammoth amount of energy comes with a mammoth price tag—about $40 million a year, according to one estimate.

Given the facility's scale and the fact that a terabyte of data can now be stored on a flash drive the size of a man's pinky, the potential amount of information that could be housed in Bluffdale is truly staggering. But so is the exponential growth in the amount of intelligence data being produced every day by the eavesdropping sensors of the NSA and other intelligence agencies. As a result of this "expanding array of theater airborne and other sensor networks," as a 2007 Department of Defense report puts it, the Pentagon is attempting to expand its worldwide communications network, known as the Global Information Grid, to handle yottabytes (10²⁴ bytes) of data. (A yottabyte is a septillion bytes—so large that no one has yet coined a term for the next higher magnitude.)

It needs that capacity because, according to a recent report by Cisco, global Internet traffic will quadruple from 2010 to 2015, reaching 966 exabytes per year. (A million exabytes equal a yottabyte.) In terms of scale, Eric Schmidt, Google's former CEO, once estimated that the total of all human knowledge created from the dawn of man to 2003 totaled 5 exabytes. And the data flow shows no sign of slowing. In 2011 more than 2 billion of the world's 6.9 billion people were connected to the Internet. By 2015, market research firm IDC estimates, there will be 2.7 billion users. Thus, the NSA's need for a 1-million-square-foot data storehouse. Should the agency ever fill the Utah center with a yottabyte of information, it would be equal to about 500 quintillion (500,000,000,000,000,000,000) pages of text.

The data stored in Bluffdale will naturally go far beyond the world's billions of public web pages. The NSA is more interested in the so-called invisible web, also known as the deep web or deepnet—data beyond the reach of the public. This includes password-protected data, US and foreign government communications, and noncommercial file-sharing between trusted peers. "The deep web contains government reports, databases, and other sources of information of high value to DOD and the intelligence community," according to a 2010 Defense Science Board report. "Alternative tools are needed to find and index data in the deep web … Stealing the classified secrets of a potential adversary is where the [intelligence] community is most comfortable." With its new Utah Data Center, the NSA will at last have the technical capability to store, and rummage through, all those stolen secrets. The question, of course, is how the agency defines who is, and who is not, "a potential adversary."

Before yottabytes of data from the deep web and elsewhere can begin piling up inside the servers of the NSA's new center, they must be collected. To better accomplish that, the agency has undergone the largest building boom in its history, including installing secret electronic monitoring rooms in major US telecom facilities. Controlled by the NSA, these highly secured spaces are where the agency taps into the US communications networks, a practice that came to light during the Bush years but was never acknowledged by the agency. The broad outlines of the so-called warrantless-wiretapping program have long been exposed—how the NSA secretly and illegally bypassed the Foreign Intelligence Surveillance Court, which was supposed to oversee and authorize highly targeted domestic eavesdropping; how the program allowed wholesale monitoring of millions of American phone calls and email. In the wake of the program's exposure, Congress passed the FISA Amendments Act of 2008, which largely made the practices legal. Telecoms that had agreed to participate in the illegal activity were granted immunity from prosecution and lawsuits. What wasn't revealed until now, however, was the enormity of this ongoing domestic spying program.

For the first time, a former NSA official has gone on the record to describe the program, codenamed Stellar Wind, in detail. William Binney was a senior NSA crypto-mathematician largely responsible for automating the agency's worldwide eavesdropping network. A tall man with strands of black hair across the front of his scalp and dark, determined eyes behind thick-rimmed glasses, the 68-year-old spent nearly four decades breaking codes and finding new ways to channel billions of private phone calls and email messages from around the world into the NSA's bulging databases. As chief and one of the two cofounders of the agency's Signals Intelligence Automation Research Center, Binney and his team designed much of the infrastructure that's still likely used to intercept international and foreign communications.