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.
But in the foothill communities of the San Gabriels, there was barely a ripple of reaction. It's hard to scare foothill dwellers, Podley contended, because of their abiding confidence in flood-control efforts and because of the spit-in-your-eye gallantry with which Southern Californians face the possibility of natural disaster.
Risk is something that comes with the territory, Podley said. Five years ago, he showed a house on Loma Alta Drive, in the northern reaches of Altadena, to a would-be buyer. "There was a fire literally burning in the forest above us at the time," he said. "The power was out and fire engines jammed the streets, but the people bought the house. Gladly."
Residents at the base of the San Gabriels said there are compensations that outweigh the risks.
"It's one of those things you buy with the property," said Donald McMullen, who has lived in Pasadena Glen, at the base of Mt. Wilson, for 30 years. "Down in the city you buy smog and toxic dumps."
Mel and Barbara Horton, McMullen's neighbors in "the Glen," a narrow canyon with rustic houses sprinkled throughout in a seemingly random fashion, talk about the beauty of their hillside community, even during the winter rains when danger always seems to loom from above.
'A Beautiful Perfume'
"You can hear the rocks rolling around up there and smell the crushed chaparral," said Barbara Horton, a retired ballet teacher who is active in conservation causes. "It's an incredibly beautiful perfume."
When they moved to the area 35 years ago, Horton added, she and her husband were "absolutely stuffed with the importance of human beings."
But living in the Glen, which is five minutes from the Foothill Freeway, has been humbling for the Hortons, who have their own horror story to tell. In 1969, during another heavy rainstorm, a torrent of mud and boulders rushed down the canyon, destroying houses and narrowly bypassing the Horton family. Piano-sized boulders tumbled past their house, and a 4-foot-thick log sprang into the air, knocking down power lines. Rails that had been sunk in the ground to slow the surge were "bent up like modern sculpture," Barbara Horton said.
"It was all over in about 10 minutes," said Mel Horton, a retired executive of a public-interest organization. "It just came charging down the canyon, dropped its huge load of boulders in the middle of the stream and then split the other way."
Nowadays, while they enjoy the awful beauty of the winter, they get apprehensive.
"You get a little tense, a little dry-mouthed," Mel Horton said.
With good reason. Pasadena Glen is one of the most precarious spots in the foothills, experts said. The head of the canyon is a narrow opening, barely wider than a man's outstretched arms, between two walls of fractured rock. A trickle of water spills through, even in the dry season, residents said. Above that is the mountain.
'Trash Rack' Protection
The only protection 55 families have from the kind of slides that the Hortons described is a "trash rack," built in 1970 by the county. A line of steel H-beams pounded into the ground to catch the debris, the rack is now jammed with boulders, gnarled tree trunks and sandy silt--2,500 cubic yards of it. Most of it was deposited there in December, when heavy rains washed debris shaken loose by last October's earthquake into the canyon, said Steve Schindler, chairman of the Pasadena Glen Improvement Assn.
The county has refused to clean out the rack because the community's main road is private. Residents signed a agreement in 1969 to maintain the area themselves, a spokeswoman said. But the residents said they signed "under duress"--the community was cut off from the outside after the 1969 deluge--and they have initiated a suit in Los Angeles County Superior Court in Pasadena for assistance from the county.
From a geologist's point of view, the San Gabriel Mountains are among the most unstable in the world, peculiarly shaped and located to encourage debris flows. Often denigrated by city dwellers as glorified piles of dirt, the San Gabriels, when measured from base plateau to peaks, are actually taller than the Rockies--by more than 2,000 feet, McPhee said.
"We are in an area of intense crustal activity here," Caltech geologist Leon Silver said. The mountain range, which stretches about 70 miles, from Valencia to San Bernardino County, actually forms part of the tattered edge between two vast continental plates, which grind unmercifully against each other, Silver said.
It doesn't take rain and fire for the San Gabriels to flake away. Erosion in the San Gabriels, a constant winnowing and drifting of small bits of silt and debris, is even more rapid in the dry weather, Morton said.
He estimated that the mountains are disappearing at a rate of 0.06 inches a year, making them among the fastest-moving mountains in the world.
Network of Basins
To control this great mass of instability, County Flood Control, which was absorbed three years ago into the Department of Public Works, has built a network of 129 debris basins and reservoirs in the county and more than 2,000 miles of paved channels and culverts to channel debris and water away from residential areas. The flood-control system, which costs the county $152 million a year, removes 1.3 million cubic yards of debris a year out of basins and reservoirs. It also dictates flood-control measures to developers who want to build on hillsides.
Berton Tibbett, a Pasadena real estate broker who has developed properties in the foothills, said that some people think the flood control district operates "like an uncontrolled giant. But they're extremely effective in protecting the Southland."
An event that occurs once a decade or so does not worry most fast-moving residents of the Southland, Silver said. But flood-control measures or not, there will be more devastating debris flows in the San Gabriel Mountains, he contended.
Is it predictable? "It's anticipatable," Silver said. "Like earthquakes, we don't know when they're coming, but we know that they're coming."