Flight 93 National Memorial Fast Facts

SHANKSVILLE, PA - SEPTEMBER 11: A visitor walks along the Wall of Names during the ceremony marking the 10th anniversary of the crash of United Flight 93 at the Flight 93 National Memorial on September 11, 2011 in Shanksville, Pennsylvania. An estimated crowd of 5,000 watched as the memorial wall was unveiled with the names of the 40 passengers who died when the plane crashed during the terrorist attacks on September 11, 2001. (Photo by Jeff Swensen/Getty Images)

(CNN)Here's a look at the Flight 93 National Memorial. It is a memorial to the 40 passengers and crew who died on United Flight 93 on September 11, 2001 near Shanksville, Pennsylvania.

When complete, the memorial will encompass 2,200 acres. It is managed by the National Park Service. One of the remaining features of the memorial is the "Tower of Voices," a 93-foot-tall tower with 40 wind chimes, which is planned for completion in 2017.
The memorial has received an average of about 300,000 visitors a year since the first features of the memorial were dedicated in 2011.
    Upon completion, features of the memorial will include the Sacred Ground memorial plaza, the "Tower of Voices," 40 memorial groves and a field of honor.
    The design was modified in 2005 after some people complained that it contained "Islamic symbolism." The National Park Service addressed concerns.
    September 11, 2001
    - United Airlines Flight 93, traveling from Newark, New Jersey, to San Francisco, crashes in a field near Shanksville, Pennsylvania. Hijackers were directing the plane towards an unknown location, but were disrupted by passengers. All 40 passengers and crew and four hijackers are killed.
    September 24, 2002 - The Flight 93 National Memorial Act is passed, creating the country's 386th national park.
    September 7, 2005 - A design by Paul Murdoch Architects of Los Angeles, "The Crescent of Embrace," is chosen for the memorial. A committee of 15 people, including family members of victims, chooses it out of more than 1,000 entries.
    August 31, 2009 - Interior Secretary Ken Salazar announces the National Park Service has reached agreements with seven of eight landowners to purchase the land necessary for the memorial, at an estimated $9.5 million. The eighth parcel, owned by Svonavec, Inc., will be taken by eminent domain after an agreement cannot be reached. This parcel includes most of the crash site.
    November 7, 2009 - The groundbreaking ceremony at the memorial site takes place.
    August 4, 2011 - The National Park Foundation announces it will match up to $2 million in donations.
    September 10, 2011 - The first features of the Flight 93 National Memorial are dedicated and opened to the public. Vice President Joe Biden attends the ceremony.
    May 30, 2012 - The National Park Service completes the planting of the 40 Memorial Groves.
    April 2013 - More than 500 volunteers plant 15,500 seedlings across 23 acres. Trees planted for reforestation in the area will serve as a windbreak for the trees in the Memorial Groves.
    October 3, 2014 - A fire breaks out at the memorial, destroying the headquarters complex. Although most of the 60,000 tribute items are stored off-site, important items, including the flag that flew over the US Capitol on September 11, 2001, are destroyed. No initial cause of the fire has been determined, but arson and foul play have been ruled out.
    February 6, 2016 - The National Park Service releases a report with the findings of its investigation into the blaze. Improperly discarded smoking material (possibly a cigarette), landscaping mulch too close to the building and flammable decking material may have fueled the fire but investigators were unable to determine exactly how the blaze started. More than 300 photographs and 25 personal mementos were lost in the fire.