In the opening moments of Ken Burns' "The Dust Bowl," several survivors of the "worst man-made ecological disaster in American history" struggle to attach a properly powerful adjective to the whole brutal ordeal.

It was "surreal," says one. "Unbelievable," offers another. Finally, an elderly woman, after giving it some careful thought, describes it as "almost evil."

Considering that similar terms were recently uttered when Superstorm Sandy wreaked horrific havoc all over the northeastern U.S., "The Dust Bowl" packs some added resonance into its two-night run on PBS. Indeed, it's one more reminder that there are forces of nature beyond our control that can drive us to our knees.

"The Dust Bowl," the latest offering from America's artsy history professor, examines the environmental catastrophe that, throughout the 1930s, turned the Great Plains into a desert, and took the lives and hopes of many.

"I don't care who describes that to you, nobody can tell it any worse than what it was," says Don Wells, a native of Boise City, Okla., in one of the many on-screen conversations. "And no one exaggerates that; there is no way for it to be exaggerated."

With "The Dust Bowl," Burns and writer Dayton Duncan deliver a film that is part visual history lesson, part cautionary tale.

Of course, all the familiar Burns trademarks are there: the expert commentaries, the celebrity voice-overs, massive amounts of archival photos, background mood music, and the sonorous narration of Peter Coyote.

The real power of the documentary lies in its 26 interviews with survivors who were just children during the Dust Bowl era. With heartfelt emotion and a down-home eloquence, they provide harrowing accounts of "black blizzards" that destroyed everything in their path, and of death, destitution and overwhelming feelings of hopelessness. At their very worst, they say, the storms seemed to portend the end of the world.

Sunday's Part 1 details how, following the passage of the Homestead Act, many residents with get-rich-quick dreams essentially raped the land by using unsustainable farming techniques. Initially, it resulted in an incredible wheat-selling boom, but a nearly decade-long drought - coupled with the Great Depression - led to what one historian calls a "natural catastrophe of biblical proportions."

Millions of acres in parts of Oklahoma, Texas, Kansas, Colorado and New Mexico were destroyed. Livestock died of suffocation. Families throughout the region struggled to maintain their sanity while dealing with outbreaks of "dust pneumonia." Burns and his team take advantage of stunning vintage images to plunge us deep into the darkness.

Yet amid all the heartbreak, there were tales of heroic perseverance as government agencies and farmers worked together to develop new farming conservation methods. Part 2 of the film largely focuses on the families who fled to California, seeking better lives.

At four hours, the film is short by Burns' standards, but the brevity is much welcome. Unlike his previous project on Prohibition, there are no gangsters and machine guns to liven things up. And the subject matter doesn't exactly lend itself to the kind of colorful characters - or even comic relief - that you might find in his epics such as "Baseball" and "Jazz."

While certainly compelling and illuminating, "The Dust Bowl" also can be quite depressing. Four hours is all we need to get the bleak and gritty picture.