It's the only rural site, a world away from the urban bustle of ground zero and the Pentagon. It's the only one Congress has designated as a national park.
And it's the only one that isn't fully funded.
Ten years after United Airlines Flight 93 slammed into a reclaimed strip mine in southwest Pennsylvania, the Flight 93 National Memorial Campaign is about $10 million short of its $62 million goal.
"It's a small price to pay to memorialize 40 people who prevented a greater terrorist attack," said King Laughlin, the memorial's chief fund-raiser.
Construction started two years ago on the 2,200-acre site, and in spite of the fund-raising obstacles it will reach a basic level of completion by the time it's dedicated today.
"We've done a tremendous amount of work in a short period of time," Laughlin said.
"Actually to be able to touch it and feel it is just amazing," said Calvin Wilson, whose brother-in-law, LeRoy Homer Jr., was Flight 93's co-pilot.
Vice President Joe Biden will attend today's dedication, and House Speaker John Boehner, R-Ohio, will lead a bipartisan delegation to the site. President Barack Obama will speak at the memorial service Sunday.
"The 10-year anniversary is going to go a long way in reigniting the interest in finishing this thing," said Rep. Bill Shuster, R-Pa.
The memorial lacks a visitor center and other signature features, including 40 tree groves, representing the passengers and crew who fought the terrorists and gave their lives.
"We're not done yet," said Gordon Felt, president of Families of Flight 93, who lost his brother Edward on 9-11. "We still have funds to raise."
It comes as no surprise that the World Trade Center memorial was funded in large part by the financial services companies that operate in Lower Manhattan. The attack took place in the heart of New York's financial district, and the sector lost many of its workers that day. Bank of America gave $20 million, and New York's billionaire mayor, Michael Bloomberg, helped raise money. At the Pentagon, the donor list includes numerous defense contractors, many of which are based nearby in northern Virginia.
But Flight 93's memorial is in a rural site, 80 miles southeast of Pittsburgh, so it has no natural source of corporate funding. The only thing that united the 33 passengers and seven crew members was the flight manifest.
Laughlin said his group reached out to every Fortune 500 company. Almost all turned him down, saying they lacked the money or the memorial didn't fit their guidelines for giving.
"We thought it was a no-brainer until corporations said it doesn't fit into their game plan," Wilson said. "I'm surprised more people haven't been kicking the door down."
Some big companies have chipped in: Pfizer, FedEx, Outback Steakhouse, Discovery Communications, Verizon and the Pittsburgh Steelers. The National Football League and the NFL Players Association have made major contributions. The Richard King Mellon Foundation made a $1 million donation.
Part of the problem, Wilson said, is where Flight 93 fits into the story of Sept. 11.
"Flight 93 has always been a footnote in 9-11, and that's unfortunate," he said. "Sometimes people don't know about the one flight that didn't hit its target. For some reason it doesn't stick, but that doesn't mean we give up."