BOSTON

A vast trove of New England sports artifacts is being preserved by a museum nestled inside Boston’s TD Garden.

The Sports Museum of New England is moving a large share of the uniforms, trophies, photos, films and other sports artifacts it has amassed over nearly four decades into secure storage, thanks to a partnership with Iron Mountain, a Boston-based records management company.

Most of the items being moved aren’t currently on display at the TD Garden, home to the NHL’s Bruins and the NBA’s Celtics. They’re part of the museum’s growing off-site collection, which includes a veritable library of primary source materials like rare films, videos, photos, scrapbooks and diaries.

Curator Richard Johnson estimates the haul represents roughly three-fourths of the museum’s total holdings, which an appraiser recently valued at $7 million.

“It’s like the underside of an iceberg,” he said on a recent tour of the museum’s exhibits at the TD Garden. “The part you don’t see is the part that makes everything else possible.”

For a city steeped in history, the Sports Museum is a somewhat untraditional repository of cultural treasures.

The exhibits, which are open daily except holidays and when there are events at the TD Garden, run about a half-mile along the expansive lobbies and narrow hallways just outside the high-priced spectator suites on the fifth and sixth floors of the arena.

While not necessarily chronological or comprehensive, they offer up a pastiche of the region’s rich sports history, with a decidedly Boston area focus.

An exhibit on the Bruins, for example, showcases one of Hall of Fame goalie Gerry Cheevers’ famous white masks from the 1970s, decorated with his signature black stitch marks. A Celtics display has a pair of size-23 sneakers worn by 7-foot-1 center Shaquille O’Neal, who played with the team during the 2010- 2011 season before retiring.

Exhibit highlights

Other exhibits highlight regional sports legends like Boston College and New England Patriots quarterback Doug Flutie; Massachusetts native and heavyweight boxing champ Rocky Marciano; and the 1980 “Miracle on Ice” U.S. Olympics men’s hockey team, which featured members of Boston University’s college squad.

Boston’s other two major league teams — the MLB’s Red Sox and the NFL’s Patriots — as well as classic New England sports events like the Boston Marathon and the Harvard-Yale football rivalry, are also showcased.

“Boston is to sports what Paris is to art,” Johnson said. “There’s a lot of territory to cover.”

The museum has found a comfortable niche at the arena, where it moved in 2000 after struggling to draw consistent patrons at its site in a mall across the Charles River in Cambridge during the 1990s.

Maintaining its off-site collection, though, has been more challenging. The collection is housed at the museum’s original home, a state-owned building museum officials say isn’t climate controlled and has been showing its age in recent years.

Rusty Sullivan, the museum’s executive director, said the organization began working with Iron Mountain after last year’s winter dumped a record 9 feet of snow on Boston and raised fears among museum staff that the collection could be at risk if the building ever sustained serious damage.

“This has been a godsend for us,” he said. “They really understood what we were up against.”

The transfer process has been going on for months. Iron Mountain officials say they’ve already taken roughly a tractor-trailer’s worth of materials from the museum. The company, which works in 36 countries on five continents, has agreed to store the collection free, in perpetuity.

The effort is part of Iron Mountain’s Living Legacy Initiative, which is also preserving letters, sneakers, flags, stuffed animals and other mementos left at the Boston Marathon finish line following the bombings that killed three people and injured hundreds more at the 2013 race.

“When it comes to paper and microfilm, these things are always in danger, even in the best non-climate controlled conditions,” said Christian Potts, a spokesman for Iron Mountain. “It may not be as dramatic as a flood or fire, but if these things don’t go to the right place, they do have a shelf life.”