Serendipity, fortified by a great deal of foresight, brought UCLA a priceless gift that fell from the skies one day in 1965.

Had it not been for an alert UCLA geography graduate student who was working at the time for Aero Service Corporation, it would have vanished altogether. Luckily, the student noticed discarded boxes of old photographs and negatives sitting on a loading dock, waiting to be hauled off to the silver recyclers.

The Aero Service Corporation had recently acquired an aerial photography business, Fairchild Aerial Surveys, for its map-making technology; it had no use, however, for Fairchild's stock of 40,000-plus old aerial photographs and negatives.

But a funny thing happened on the way to meltdown.

The graduate student rushed to call Professor Ben Thomas, then-chair of UCLA's geography department, who wisely sized up a golden opportunity. He immediately rented a truck and dispatched a group of graduate students to the loading dock.

"The students showed up with the truck and just started tossing the boxes in," recounted John Franklin, curator of what is now the department's Air Photo Archives. "They didn't really know what they were getting."

They have since become a lot wiser.

The collection that the company gave to UCLA comprises an invaluable visual record of the growth of America, a black-and-white history documented by aerial photographers who crisscrossed the country from 1921 to 1965, flying at low altitude over countless towns, cities and geographic landmarks from California across 30 states to New York.

Now catalogued in two separate groups focusing on Southern California and the rest of the nation, the Fairchild Collection and an equally important acquisition, the Spence Air Photos, draw hundreds of visitors each year to the UCLA Geography Air Photo Archives. Customers pay $30 an hour to peruse the archive, considered by many to be the best repository for aerial oblique photographs in the nation. It marks its 37th anniversary this year.

"We like to say we're antique, oblique and unique," jested Franklin, standing amidst rows of packed file cabinets on the ground level of Bunche Hall.

Aerial photos taken at an oblique, rather than vertical, angle have the singular advantage of capturing a scene in superb detail. Rather than a flat view of the landscape, taken with a camera pointed straight down from a plane, oblique photos show the horizon and the undulating hills and valleys of the entire landscape.

A day after the St. Francis Dam collapsed March 12, 1928, sending billions of gallons of water through San Francisquito Canyon; Bob Spence took dramatic photos of the aftermath of this major disaster. Only a section of the structure remained intact. The deadly 10-story wall of water killed more than 450 people as it rushed toward the ocean.

"You don't see just rooftops," Franklin noted. "You can see right into people's yards, the signs on buildings, and people working. You see the cars parked out front of the houses, the foliage on the trees, the lay of the land. There's a built-in three-dimensionality to them."

Fairchild shot for both private and public clients, like the State of New York and many cities. "Fairchild photographed most of New England and the eastern seaboard in great detail," the curator said. "These photographs are more important to us now because there are very few aerial photographic records, especially oblique ones, of that area of the country."

For example, much of the history of New York City, as it developed over the first half of the 20th century, unfolds in 780 shots dating from 1921 to 1955. "Some are fabulously beautiful, taken at sunset or through thick fog. They are even more poignant after the events of Sept. 11," Franklin said.

The Spence collection, which dates back to 1920, offers the viewer something else: historical depth, with more than 110,000 photographs and negatives, most of them glimpses of Southern California over 51 years. This span was interrupted only when Robert Spence did aerial surveys of the Burma theater for the Army Air Corps during World War II.

For the most part, Spence kept the Southern California region in his viewfinder -- the San Andreas fault; a football game at the Rose Bowl in 1928; the crumbled remains of the St. Francis Dam a day after it collapsed in 1928, releasing more than 12 billion gallons of water and killing 450 people.

"He has given us a view of Southern California over time that is impossible to find anywhere else," Franklin said.

Leaning out of the cockpit as he held on to a giant, 46-pound camera that was nearly half his body weight, Spence was passionate about his work. "When he flew out to take a picture for a client, he would shoot on the way out and back, partly as a speculative effort and partly as a historian," Franklin said. "He was an inveterate aerial historian."

Back in the '20s, when flying was still a novelty, people paid a hefty $10 apiece for an aerial shot of their home or business. "Spence happened to catch that wave in the '20s and he rode it all the way till the Depression years," Franklin said.

When Spence retired at age 77, he offered his collection first to UC Berkeley. But because it concentrated heavily on Southern California, Berkeley wasn't interested. Again, UCLA's Department of Geography quickly stepped up to take it and credited Spence with a $50,000 donation.

"The negatives today are a priceless record when you consider that you can make thousands of photographs from them," Franklin said. Stored on earthquake-proof shelves in refrigerated vaults, the negatives have kept student employees busy for years with the job of archiving them.

Today, the archive draws a wide assortment of customers who pay $35-$80 for a single glossy.

Some come hunting for a link to the past, searching for photographs of empty or barely developed land where their sprawling housing tract now stands. "Folks come in from Malibu to try and find photos of their house when it was the only one on the beach," Franklin said, smiling.

Homeowners caught in disputes with city inspectors or neighbors over when their property was graded or where property lines or a fence once existed search the archive for historical proof in black-and-white.

One homeowner who was being accused by city inspectors of building a portico onto his beach house without a permit found early photos of the house that showed the portico existed before a permit was required. With an enlarged aerial photo in hand, he easily won his argument with the city.

But the archive's primary customers are environmental consultants looking for evidence of past pollution. They research the historical uses of sites that are up for sale. With magnifying lenses, they carefully scan early photographs for any sign of a chrome-plating plant, gas station or other possible source of pollution in the hope of avoiding heavy cleanup costs for their clients -- commercial developers or lending institutions.

A new book by Tom Campanella, assistant professor of city planning at the University of North Carolina, Chapel Hill, has been recently released featuring 150 photographs from the Fairchild Collection. "Cities from the Sky" is being published by Princeton University Architectural Press and is now available in bookstores.

The archive is open by appointment only at 1221 D Bunche Hall. Call (310) 206-8188. For more information, go to www.geog.ucla.edu/airphoto.html or e-mail airphoto@geog.ucla.edu.