Documentary filmmaker Ken Burns was in Washington, D.C., on Tuesday to witness what he calls the beginning of the third act in American history.

Two days later, Burns shared the experience with several hundred Outdoor Industry Association members in Salt Lake City for the 2009 Outdoor Retailer Winter Market.

"After the birth of my three daughters, I cannot think of something that has meant more to me," he said of the inauguration of Barack Obama, the first African-American to be sworn in as president of the United States.

Race has played a major part in several of Burns' documentaries, including "The Civil War," "Baseball," "Jazz" and "Unforgivable Blackness: The Rise and Fall of Jack Johnson."

"You cannot scrape the surface of American history without dealing with it," he said.

Over the past 30 years, Burns has done much more than scrape the surface of U.S. history. In the words of the late historian Stephen Ambrose, "More Americans get their history from Ken Burns than any other source."

Through film, Burns has attempted to understand how the U.S. works. The goal with each film, Burns said, is to move one step closer to understanding the "deceptively simple" question: Who are we?

"You never answer it," he said. "It deepens with each successive project we work on."

Burns did, however, offer an answer to a related question: When are we?

"We are all in the wake of one of the most amazing moments in our history — the beginning of our third act," he said.

According to Burns, the first act began in 1776 when Thomas Jefferson, the subject of his 1997 biographical film, declared: "We hold these truths to be self-evident, that all men are created equal."

"But he only meant all white men of property, free of debt," Burns said.

The second act, he said, began "four score and seven years" later, "when Abraham Lincoln traveled to Gettysburg on Nov. 19, 1863, and told us we had a new birth of freedom, that we actually really did mean that all men are created equal."

"But we as a nation did nothing about that for 100 years," Burns said, "and then it took another two generations, and suddenly on Tuesday at four minutes after 12, we began our third act as a people."

Burns' latest project is "The National Parks: America's Best Idea," a 12-hour, six-part history of U.S. national parks. The film, which Burns says is the best he's ever done, begins airing on PBS in late September.

Burns calls Americans' relationship with nature "unlike any other country on earth," and that led to creation of national parks.