The National Security Agency is closing the secretive listening post it has quietly operated north of Yakima since the early 1970s.

Located securely within the Army's Yakima Training Center, the facility has operated with little fanfare and much speculation for decades. It has been linked to Echelon, a global surveillance network operated by the NSA.

An attempt to reach an NSA spokesperson Wednesday was unsuccessful, but U.S. Rep. Doc Hastings' office confirmed some details of the closure of what's called the Yakima Research Station.

Hastings, whose 4th Congressional District includes the NSA facility, was informed of the pending closure last summer by the NSA, according to his news secretary, Neal Kirby.

The closure is part of NSA's effort to streamline and reorganize, with some of the Yakima functions being moved to Colorado, he said.

An exact date of closure was not available Wednesday afternoon, while the number of employees at the facility is considered classified, he said.

The electronic eavesdropping operation includes several buildings and a collection of large white satellite dishes set amid the rolling arid steppe land of the military reservation. Motorists on Interstate 82 about eight miles west of Yakima can catch a glimpse of the operation in the distance.

Access is highly restricted. The training center, a 327,000-acre Army base used primarily for artillery training and target practice, does not mention the facility on its website. And the Army routinely refers any inquiries about the facility to the NSA, which is based in Fort Meade, Md.

The Yakima facility has been mentioned in several books on national security, but otherwise hasn't attracted widespread attention.

James Bamford, whose groundbreaking 1982 book about the NSA, "The Puzzle Palace," and others have said the Yakima Research Station has played a major role for decades in Echelon, the global surveillance network operated by the NSA and its counterparts in the British Commonwealth - Britain, Canada, Australia and New Zealand. The system has been reported to be capable of intercepting satellite communications traffic, such as emails and calls, from cellphones.

In a 2006 interview with the Yakima Herald-Republic, Bamford noted the Yakima facility, like the agency, is cloaked in secrecy.

"It doesn't make noise, doesn't send smoke," he said. "It's almost invisible. The whole agency is virtually invisible."

In a 2002 interview with the Newhouse News Service, Bamford said the Yakima facility obtains about 2 million intercepts per hour.

The NSA was created by President Harry S. Truman in 1952. Its core missions are described as protecting U.S. national security systems and producing foreign signals intelligence information.

In the early years, the agency focused on wiretapping telephones and telegraph lines. But experts say that by the late 1960s, the NSA had an array of listening posts capable of intercepting satellite signals.

Some experts estimate that the NSA has 38,000 to 52,000 employees worldwide.