County flood-control officials have a videotape, shot by a fixed camera during a rainstorm in Japan, of a sudden rush of debris down a mountain. First, you see an empty channel, 30 feet wide and paved, stretching down the side of the mountain. There's a little commotion in the distance, way up near the top. Suddenly, the front of a huge, boiling mass of boulders and mud sweeps past, with the concentrated force of a rampaging steam locomotive.
"That's what happened up in Shields Canyon," said Garvin Pederson, assistant division engineer for the Los Angeles County Department of Public Works, as the flow of violently churning debris continues on the screen, slopping over the sides of the channel and splashing the lens of the camera.
As have many officials and academics in recent weeks, Pederson has been talking about a short, almost lethal episode in 1978, in which a family in a mountain area of La Crescenta was trapped in their house as mud and rocks oozed implacably through doors and windows.
That episode and others were described at length by writer John McPhee in a recent two-part series in the New Yorker about "debris flows" in the San Gabriel Mountains. A writer known for his quirky passions (he has written books about oranges, Alaska and bark canoes, among other topics), McPhee attacked the subject with a characteristic blend of carefully constructed metaphor and dense factual detail.
He also raised some troubling questions about man's Lilliputian efforts to control debris flows, as geologists call the violent mudslides and landslides that occur in the mountains during rainstorms.
When it comes to major geological events, McPhee suggested, with the concurrence of a lot of geologists, the vast protective network of culverts, channels and debris basins built by the Los Angeles County Flood Control District is like a match stick in the path of a steamroller. Under extreme circumstances, county efforts to protect homes and communities jammed against the base of the mountains are "unexampled in heroic chutzpah," McPhee wrote.
Take Shields Canyon, where, on the night of Feb. 10, 1978, Bob and Jackie Genofile and their two children were living on a promontory overlooking Glendale. One of the worst storms in the history of Southern California dumped about 6 inches of rain on the area in 24 hours that day. During a particularly intense 25-minute period, an inch and a half of water fell in the canyon.
Suddenly, a 6-foot-high "slug" of debris descended on the Genofiles' home. McPhee described the family huddled in a bedroom, each parent clutching a child, fatalistically resigned to drowning in mud:
"The house became buried to the eaves. Boulders sat on the roof. Thirteen automobiles were packed around the building, including five in the pool. A din of rock kept banging against them. The stuck horn of a buried car was blaring. The family in the darkness in their fixed tableau watched one another by the light of a directional signal, endlessly blinking. The house had filled up in six minutes, and the mud stopped rising near the children's chins."
Ironically, McPhee wrote, the Genofiles' home was "bracketed with debris basins," bowl-like cavities in the ground designed to catch the spillover before it reaches residential areas. Above the house was a debris basin with a capacity of 6,000 cubic yards, with paved trenches leading to a larger one below.
Pederson puts on a tape showing Shields Canyon the day after the Genofiles' house filled up. There's a glimpse of the house buried in enough debris so that there is just a short step from ground level to roof. The mud still streams through the canyon, a gloppy mix of rocks, dirt and water. The camera pans across the hill above the house. A great piece of the hilltop has obviously fallen away, like a giant wedge of halvah sliced from a loaf.
The rush of falling material quickly filled the upper debris basin, Pederson said. "What happened was that one of the channels that feeds the Shields Debris Basin got plugged," he said. "The mud overflowed and hit the house."
Ultimately, the Genofiles sued the county, claiming that the flood-control network had not been properly maintained, and won a $337,500 settlement.
Despite a number of scary stories like the Genofiles' in McPhee's articles, including vivid accounts of people killed and houses swept away, there has been no rush to unload mountain property, local real estate brokers said. Perhaps it is because the articles appeared in an East Coast publication with a reputation for polished but obtuse literary works and sophisticated commentary.
"I'm very curious as to why the New Yorker would have an article about the San Gabriel Mountains," said William Podley, a real estate broker from Pasadena, who had not read McPhee's work.