That 1982 map—made well before the advent of computerized geographical information systems, known as GIS—is not detailed enough to show all landslide-prone areas. The mapmakers warned that "individual landslides could not be shown on a map of this scale." And in fact it does not show any hazard in the Oso area, which was well documented in state studies.
"It was never intended as a map to be used for specific areas of the country," said Peter Lyttle, program coordinator for landslide mitigation at USGS headquarters in Reston, Va. "It's a cartoon graphic to show which areas are prone to landslides: the Appalachians, the West Coast, the Mountain West."
While drawing conclusions from such a crude representation is problematic, NBC News and the computer mapping firm ESRI plugged in Census data to see how population has changed in the areas identified on the map since it was drawn. Adding together all the landslide-prone areas on the map, ESRI found that the total 2000 population living in such zones was 77.2 million. By 2010, the population in those same boundaries had increased by 7 percent to 82.7 million. And by 2013, the population rose another 1.6 percent to 84.0 million—or 26 percent of the current U.S. population. ESRI's projections show that these areas are expected to add another 3.2 percent by 2018, pushing the population to 86.7 million.
The areas also include about 13 million housing units built after the 1982 map was published, ESRI calculated.
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Congress gave the USGS a mandate a decade ago to set a national policy to mitigate landslide risks. The USGS estimated that the cost would be $25 million a year, and the National Academy of Sciences offered a higher estimate, $50 million. Instead, Congress allocated only $2.5 million, which has slowly increased to $3.5 million, Lyttle said.
"The plan and the reality are two different things," Highland said. "Congress tells us we need to have a national strategy, but they don't give us the money to do it."
The agency has focused on discrete, modest projects: developing a warning system in areas where major landslides have reduced stabilizing vegetation, setting levels in the Seattle area for warnings after major rainfall that could undermine slopes.
Several states have good landslide maps, Highland said, and she is coordinating a pilot program to get states to cooperate on standards and definitions. Washington, Oregon, and California are among the states with the most complete inventories of landslide hazards, and she named Kentucky, Ohio and West Virginia as other states with particularly good efforts.
Most worrisome, she said, was the North Carolina experience.
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In September 2004, western North Carolina was hit by rains from Hurricane Francis, then two weeks later by Hurricane Ivan. Saturated ground in the mountains then gave way, and the Peek's Creek landslide killed five people and destroyed 15 homes. It cost about $1.3 million to clean up, and $3.2 million to buy out damaged property.
The legislature approved a program to map landslide risks in 19 western counties. State geologist Rick Wooten put a team together, using lidar, the newest technology to help detect changes in the ground with lasers. In one county, the team found more than 2,000 landslides triggered by a storm in the 1940s.
"I know we were making a good scientific product," Wooten said. "We had peer review. We had the right skill set of people working on it."
One member of that team, a young geologist named Jennifer Bauer, went to work making a map in her home county in the mountains. "I grew up in Macon County," she said. "Even growing up here, I was not aware that landslides happen in North Carolina."
The work was slow, taking about one year per county, at a cost of about $500,000. In comparison, a landslide in Maggie Valley, N.C., in 2009 cost about $1.4 million to clean up.
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"The cost of the mapping to complete an entire county is less than or equivalent to the average home in the county," Bauer said. "If we can save one home from getting destroyed, it pays for the mapping for the entire county."
But the geologists often encountered anxiety as they worked. Real estate agents feared that they would be held responsible legally if they failed to disclose a hazard area to a buyer. Builders were concerned that land values would fall. "A lot of what we were hearing was a lot of misperceptions," Bauer said. "The map didn't say you couldn't build here. It says here's information you can use, where you really need to pay attention."
In the state capital, the program became a target. The legislator who had proposed the mapping, Rep. Ray Rapp, also had proposed legislation to regulate development in areas with a slope of at least 40 percent. Three times the legislature soundly rejected his steep-slope law, which was opposed vigorously by the home builders and Realtors associations.
One influential Republican, state Rep. Mitch Gillespie of Marion, had taped a bull's-eye target on his office window, positioned so dead center was right over the nearby offices of the state Department of Natural Resources. He told reporters that the mapping cuts were part of a general budget reduction, but he often added that the mapping was unnecessary and was being done to bolster efforts to reduce development.
After Republicans took control of the Legislature in 2011 for the first time since 1870, lawmakers killed the maps and furloughed the five geologists. A Republican state senator, Don East, told the Associated Press that the cuts "will get government off the backs of business and industry."
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Rapp was defeated in 2012 after redistricting changed his district to a more Republican population. He said Realtors, who had backed his previous campaigns, also withdrew their support.
Gillespie, who opposed the mapping, was re-elected, but left the legislature. Now he has an office in the building he once had a bull's-eye on, as assistant secretary for the environment at the Department of Natural Resources.
The North Carolina Association of Realtors did not respond to requests from NBC News for comment. The association's members had discussed publicly their fears that they might be held accountable for disclosing to property owners landslide risks shown on the map. (California has such a requirement, but most states do not.)
At the North Carolina Home Builders Association, the general counsel and executive vice president, Michael Carpenter, said he didn't believe the group has a policy now on the mapping, which he said is a dead issue in the legislature. "Generally speaking, I'm sure there are areas in which there ought to be protection," he said, but he questioned the science. "How useful is the mapping? How accurate is it? I don't know enough about the science to say."
Bauer, one of the geologists on the state team, went into business with another team member in Asheville, advising homeowners on their landslide risks. "People still want to know this information," she said. "The scientists knew what was going on, but the public didn't."
Mapping team leader Wooten kept his state job, but he said he got the message that the legislature doesn't want anyone on the payroll mapping landslides.
"We're not a regulatory agency," Wooten said. "We weren't promoting or fighting against regulations on mountainside development. Our job was just to make the maps, so people could make informed decisions about where to build.
"Politically and socially, it's a hard thing to do," Wooten said. "I hope we can get to a point where there will be science education, where people will understand nuance, public education, relative risk. But I'm not sure I'll live long enough."