Christopher Rauschenberg composed panoramas of multiple frames to evoke the expanse of the Pacific Science Center Courtyard in Seattle, where Minoru Yamasaki's white sculptured arches evoke his later design for the World Trade Center towers. Mr. Rauschenberg used the same technique to capture the Mill Creek Canyon Earthworks in Kent, Wash., an environmental artwork by Herbert Bayer composed of mounds and excavated concentric circles intended to collect storm water.
Mr. Fox hung out of a small helicopter hovering at 500 to 1,500 feet to capture the hub-and-spoke design of Parkmerced in San Francisco, often described as a city within a city with landscape architecture by Thomas D. Church with Robert Royston and a model of postwar urban planning.
Heather F. Wetzel used the 19th-century technique of ruby ambrotype to render dark clouds hovering above Lake Elizabeth, the trapezoidal gem designed by Mr. Simonds for the 1967 renewal of the Allegheny Commons in Pittsburgh.
"I'm not a fanatic on preservation," said Mr. Friedberg, 77, whose Peavey Plaza in Minneapolis is listed among the "Marvels." "I don't think everything I've done deserves to be preserved. I think it works at the time, and then we go from there."
Still, he argued that the values embedded in the original design should be honored as time unfolds. "So often there is no basis for criteria," he said. "Some banal administrator makes a decision on the basis of his own needs and feeble desires. There should be a national committee, an organization that is given responsibility for arbitrating and assessing these things."
Mr. Friedberg estimates that the United States had about 5,000 landscape architects in 1965. According to the Bureau of Labor Statistics, that number soared to 28,000 by 2006. (Mr. Birnbaum and Mr. Friedberg estimate it is closer to 35,000 or 40,000).
As the profession grows, so does Mr. Birnbaum's organization. Next year its Web site (www.tclf.org), already a veritable garden of factual accounts and written and oral histories, will be "updated to 2.0 so that everything will be linked and Wiki-like," he said.
"What's Out There?," a major project in development for 10 years, will allow users to type in a geographic location, designer or landscape style and bring up visual and written records. A downloadable form will encourage people to submit entries of heretofore forgotten landscapes that will then be vetted by a project manager and posted. And a segment called "You Tell Us" will seek submissions of detailed narratives by those who worked on those creations or who watched from the sidelines.
Part of the larger problem, Mr. Birnbaum said, is that no one really knows what is out there. As layers are added to the collective scholarship of the nationís landscape heritage, he and other enthusiasts will be able to fit together histories like Russian nesting dolls and discern how they stack up. They will also have to determine which are the most important.
"Many of the landscapes that are on our list this year will quite easily die a quiet death," Mr. Birnbaum said. "And so what we want to do is make them visible, put a bit of light on them so that they too have a discourse instead of letting them one day just be gone. They've deserved it."