SALT LAKE CITY — The LDS Church is opening its storied vault — albeit in a virtual kind of way.

Kicking off the national Family History Conference at the Salt Palace Convention Center was Wednesday morning's virtual video tour of the Granite Mountain Records Vault, the seldom-seen site of records preservation and storage for The Church of Jesus Christ of Latter-day Saints.

Granite Mountain is home to some 35 billion images of genealogical information, contained mostly on 2.4 million rolls of microfilm, said Jay L. Verkler, managing director of the church's Family History Department and presenter of Wednesday's "tour."

Some 50-plus employees work at the secluded vault site, where records are stored, copied and digitized.

Granite Mountain doubles as a deep-storage facility protecting materials key to church operations, leadership and history.

If the casual observer sees LDS temples as being semi-secret, then the average Mormon may have similar leanings about the facility located not far up Little Cottonwood Canyon.

But church officials say Granite Mountain's protective status is not to be secretive as much as secure.

It's not a unique set-up. Large commercial or government perpetual storage sites are found in states like Kansas, Pennsylvania, Alabama, and Virginia. A private enterprise using similar tunnels is a Little Cottonwood Canyon neighbor.

"Archiving is a trick," Verkler said. "They [archivists] don't want patrons touching their records."

Archivists are also concerned with the slightest contamination, including "blue jean dust," the cotton fibers created by brushing pant legs when large groups walk by, said Brent Thompson, director of the Church History Department's preservation services.

"In our business, we don't want foreign materials — we don't want the dust off their shoes, we don't want the fibers off their clothing," Thompson said.

"It's a preservation facility," he added. "If we are marching visitors through frequently, it would be hard to maintain temperatures and keep it under control."

In the late 1930s, the LDS Church's Genealogy Society of Utah began microfilming genealogical records. After amassing more than 100,000 rolls through the next decade and a half, a permanent storage site was needed.

Church officials considered preservation and storage operations as part of an $8 million, 15-story archival building on the corner of Main and North Temple streets, where the new Church History Library now sits.

"It was a great blessing that didn't happen," said Thompson, explaining mid-'50s storage technology was limited and construction lacked seismic codes.

Other potential sites included City Creek and Red Butte canyons, until an engineer/architect living in a cottage in Little Cottonwood Canyon remembered its sheer, vertical granite cliffs. He suggested tunnels into the rock might provide maximum protection and temperature stability.

Testing in the late '50s prompted the church to go full bore; blasting and excavating began in May 1960.

Crews drilled the arched tunnels 10 feet at a time, using ammonium sulfate and diesel fuel to blast every other night. On alternate days, the crews hauled out excess rock.

After tunneling nearly 700 feet without encountering cracks or fissures, the excavation met two challenges — water, and a different type of rock. Crews couldn't go farther.

"Finding that water was very valuable — it was a very big blessing," said Thompson, noting water is used for processing and washing off microfilm as well as in restrooms and heating and cooling systems.

The first microfilm rolls were transferred in April 1963, even though construction wasn't completed until the following December, when the facility was open for public tours.

Visitors described the three long, narrow corridors and four cross tunnels, while media reports noted the $2 million price tag. Some 675 feet of granite rock guarded the tunnels from above, and reinforced entrance doors weighing 9 to 14 tons each were said to be able to withstand a nuclear blast.

Steel and concrete lined the tunnels, with banks of metal storage cabinets reaching 10 feet high. The arched interiors were painted in pastel colors, the Deseret News reported, "to alleviate the monotony and eliminate the cavernous atmosphere."

The site was fully operational in 1965, named in May 1966 and dedicated on June 22, 1966.

Forty-plus years later, the vault boasts the world's largest collection of family history information.

Microfilm masters — negatives used for duplication and digitization — occupy 60 percent of Granite Mountain's space. Duplicate rolls are sent to the Family History Library, family history centers and patrons to the tune of 4 million images a week. Digital images are indexed and used in online research.

Digitization started in 2002 as a tedious process. Scanners of that era had trouble reading underexposed and overexposed images as light densities varied even on the same microfilm roll, meaning operators had to closely watch for problems, stop, back up, readjust and repeat.

Conversion to digital images was projected then to take more than a century, Verkler said.

The church has worked with international scanner manufacturers to develop improved scan rates and procedures. "We think we're going to be producing 10 times the images we were five years ago," Verkler said.

Thompson cites two advantages provided by the granite mountainside vault — a protected environment from intruders, fire, earthquake and disaster as well as a stable storage environment. Improvements in 2001 led to constants of 55-degree temperature and 35 percent humidity.

Besides genealogical preservation and storage, Granite Mountain Records Vault serves as the deep archives for a myriad of church materials — including scriptures in every language published, large leather-bound temple ordinance books that were hand-kept through the 1960s, materials and minutes from presiding priesthood quorums, financial records, backup tapes and audio-visual masters from "Legacy" to "Johnny Lingo."

"Once the original records are there, they generally don't leave," said Thompson.

Nor likely seen or touched either.