The Control of Nature

McPhee returns to the horror of the Genofiles, who were trapped in their home due to the debris flow. Rescuers bypassed their house as they assumed the family members had perished. A neighbor finally approached, and the family solicited help. Two debris basins surround the Genofiles and their neighbors: Upper Shields basin on top and Shields basin below them. A Flood vehicle went to check on Shields Debris Basin, but the debris broke through the basin and chased the truck. The Flood workers escaped, but the debris hits the Genofiles’ neighborhood. McPhee describes the massive amounts of debris that covered the area, including debris covering palm trees and crushing cars. The Genofiles examined the damage after escaping from their house. The Genofiles remark that they did not feel they were in any kind of danger prior to the debris storm; they were confident in the security of the debris basins. After the storm, the Genofiles suffered from anxiety and would often wake up in the middle of the night. The family rebuilt their house. They also sued Los Angeles County on the grounds of poor maintenance of the Upper Shields Debris Basin. The county paid the Genofiles more than $300,000.

Debris flows take place at different times and at different spots on the mountain; they lack consistency in terms of timing and size. Nonetheless, people continue to build homes in the area. McPhee spends some time with Wade Wells, who works for the United States Forest Service and researches erosion in the San Gabriel Mountains. The mountains occupy a unique spot right next to the bustling, urban Los Angeles County. From the mountains, sea fog and pollution-induced smog obscure the city of Los Angeles. McPhee accompanies Wade and another scientist up the mountain, where they take soil samples. McPhee points out the plant life on the steep slopes of the mountains—often referred to as “oversteepened”—including thick, prickly bush known as chaparral, which accumulates during droughts.

McPhee notes that the chaparral depends on fire. Some chaparral will only grow in the aftermath of a fire. The chaparral also relies on fire to burn through dead brush and return the plants’ nutrients to the soil. McPhee also describes the southwesterly breeze that flows through this area, which is famously known as the Santa Ana wind. The Santa Anas also raise the threat of severe fire, particularly as they crash into local mountain winds, thus scattering fires all over the county. McPhee notes the Southern California chaparral lays claims to the highest intensity and greatest frequency of forest fires in the country. Chaparral fires burn every 30 years, but before human settlement, the fires were smaller. Now that humans suppress fires through chemicals and other means, there is a large amount of brush left on the mountains. Therefore, when the brush catches on fire, the burns are hotter and faster than in the days prior to human settlement, because there is more vegetation to burn.

Under the chaparral, loose soil and rocks collect, leading to erosion—especially in the aftermath of a fire. McPhee refers to the tumbling of this mountain dirt as “dry ravel.” McPhee says that “so much dry ravel and other debris becomes piled up and ready to go that to live under one of those canyons is (as many have said) to look up to the barrel of a gun” (212). Using Wade’s soil experiments, McPhee demonstrates how unburnt chaparral—and the soil underneath—is somewhat resistant to soaking up rainwater, contributing to debris flows. As rain flows down the mountainside, rills—or miniature streambeds on the mountain—appear, collectively forming a rill network. The rill network increases the speed of erosion as the water that it mobilizes hits the debris collected at the bottom of the canyon. Although Los Angeles does not receive total annual rainfall—often only five inches—it has among the highest concentrations of rainfall in the country. McPhee explains this seeming contradiction by noting that certain storms will roll in from the Pacific Ocean and dump large amounts of water from the oceans into the mountains in a short period of time. 

A few miles into the mountain lies a watershed. The Middle Fork of Mill Creek—a tributary of the Big Tujunga, which is one of the three major rivers of Los Angeles County—drains this watershed. Sometimes, city dwellers go to the mountains to fire guns as a hobby. One day in 1977, a hobby gunman stuffed his rifle with Kleenex. When he fired the rifle, black powder in the rifle ignited with the Kleenex, which shot out of the rifle and burned down thousands of acres—including the Middle Fork watershed. The chaparral in the area was more prone to intense fire, since it had not burned in nearly a century. Further down from the fire was the community of Hidden Springs, which sat underneath 300,000-plus cubic yards of loose debris. Two engineers with Los Angeles County’s fire department informed the Hidden Springs residents about the imminent danger facing them, but the residents didn’t believe the engineers.

In the winter, there was an excessive amount of rainfall in Hidden Springs. In February of 1978, a fire occurred, and people assisted in putting out the fire, though the heavy rainfall also helped. However, the rainfall set off a massive debris flow, killing 13 people and sweeping survivors—including Amos Lewis—off their feet. Houses tore in half. Bridges broke. Lewis survived by hanging onto a tree branch above the flow. Lewis helped excavate the remains of victims of the flow. Lewis shows McPhee and Wade Wells a few cinder block foundations, which is what remains of the houses after the debris flow. Much of the mud and rock from the debris flow wound up in the Big Tujunga River, leading the county to spend millions to remove the debris from the river.

McPhee describes the stream valleys of the San Gabriel mountains, including the school bus-sized boulders in the valleys. These boulders occasionally tumble into residential neighborhoods. Mike Rubel builds his home—a castle—out of debris boulders. McPhee admires Rubel’s house. On a whim, McPhee visits a university, Caltech, and is introduced to the geologist Leon Silver. McPhee and Silver chat about the rocks in the mountains surrounding the university, which have shattered due to earthquakes. The earthquake aftershocks and the shattering rocks contribute to the greater likelihood of debris flows. McPhee describes the unstable rock moving down the mountain. This movement of dirt down the mountain produces steep slopes—right next to the homes of Los Angeles County.

Specifically, McPhee refers to the continuous tectonic front, which is where two major plates under the Earth’s surface—the North American and Pacific—move next to each other. These two plates form a kink in the San Andreas fault, the tectonic boundary between the two plates. McPhee uses a simple line with a kink in it to represent a bend in the San Andreas Fault, which he likens to a chair. McPhee writes, “Los Angeles is like a wad of gum stuck to that chair” (226). The kink in the fault is known as the Transverse Ranges. As the two plates move about the San Andreas, the terrain at the kink gets squeezed, thus compressing the San Gabriel mountains by a tenth of an inch each year. However, Silver notes that the mountains are rising at a more rapid pace than they are sinking. The aforementioned debris basins allow scientists to study the erosion of the San Gabriels.

Silver says that most people who live near the mountains are not aware of the risks. He also admits that he once lived next to the mountainside. When McPhee asks Silver why he lived there, Silver replies that he took a risk, because it’s cooler up in the mountains and there are ideal views of the city. McPhee interviews Silver’s colleague Barclay Kamb, who has studied the Sierra Madre Fault zone of the San Gabriels. Kamb states that humans build crib structures above the debris basins to restrict sediment flow from canyons in the mountains. This is faulty logic, however, because the sediment ends up being stored in these cribs, which are not as strong natural barriers and will likely end up scattering the debris during natural disasters. McPhee meets other scientists and engineers who also criticize the crib structures. 

McPhee provides a snapshot of a block in the city of Glendora that contains many citrus trees. McPhee notes that this citrus tree block has since been bulldozed for a new housing development. McPhee introduces Charles Colver, who manages an experimental forest in the mountains. Colver recollects a time when a bulk load—a debris flow with mud and trees—came down the mountain. The bulk load toppled a citrus grove. Even with the debris, the fruit growers planted new trees. The trees adapted to the debris, unlike houses.

McPhee dives into the history of this area, including the Asuksangna—a Native American tribe that resided there prior to white colonization. The village of the Asuksangna is known today as Azusa. The Asuksangna burned grasslands seasonally for agricultural reasons, thereby inadvertently setting chaparral on fire and loosening debris flows. However, they also adjusted to the debris flow. The ranchers who followed the Native Americans wound up fighting each other over the water in the area, even though that water carried loads from the mountain that could kill them. Drought killed many of the cattle in the 1860s. McPhee writes, “The message was clear: this environment was no less than hostile than it was appealing” (235).

The arrival of railroads in California led to a population boom. Farmers moved to the state and planted citrus groves. The ditches in the mountainside watered the trees, but the ditches also became choked with debris. A debris flow wrecked a railroad line. Electric streetcars developed, and communities began to form in the area. Wildfires led to debris flows in 1914, which led to the creation of the Los Angeles County Flood Control District (also known as “Flood”). However, people love the freedom that comes with living out in nature and away from the city. McPhee interviews a few present-day residents in a place called Pasadena Glen. They describe the terrifying sound of falling boulders and the smell of crushed chaparral, as well as the peaceful stillness of the area. A lot of rain in a short period of time causes a destructive debris flow. After the 1969 event, the Forest Service converted a stream to a concrete bed, which was intended to protect the properties below.

McPhee returns to the 1930s history of the area. Chaparral burned in the canyons above numerous towns in 1933. Massive rainfall followed, launching several debris flows at once known as the New Year’s Day Flood. Hundreds of homes collapsed. Dozens of people died. Fortunately, a gravel pit filled up with debris—and later became a debris basin—saving the village of Tujunga from decimation. McPhee asserts that floods of rock are more dangerous than floods of water in these areas. During World War II, wartime industries led to a population boom in Los Angeles. The county created housing for these newcomers by cutting down citrus trees for development. Urbanization clashed with agriculture as residents complained about smelly fertilizer, smog harmed the quality of fruit, and growers sold their land to developers. The earliest debris basins in Los Angeles overflowed, but eventually, the basins became more efficient at catching debris.

Debris basins don’t sit underneath every canyon, however. In the span of three years in the 1970s, three separate debris flows hit the home of the McNamara family in Glendale. They couldn’t sell their home as buyers would be wary of purchasing it. Also, debris basins could not handle all dangers the same. A basin might be fine at holding back debris flow one year and bad the next. People who live in these areas grow calm in the face of such danger. They believe that they have built sufficient defense mechanisms to defend them. As one resident tells McPhee: “People live here, come hell or high water. Both come, and we’ll still stay” (245). 

McPhee talks to a geologist who tells him that many people have little idea of the threat that comes with living in these mountainous areas, as they purchased their home after the last debris flow. Not only does the county of Los Angeles subsidize the risk of living in these areas through the erection barriers, but so, too, does the federal government, which provides insurance in the case of houses lost to flows. However, most of the homeowners in these areas don’t have insurance against debris flows, as they calculate their odds of their home getting hit by a debris flow to be low. After a fire, the county of Los Angeles prepared homeowners for the debris flows they might face once rain hit the area, but the people of Glendora maintained that their town didn’t do enough to prevent debris flows, and they sued their town. The town of Glendora lost the lawsuit. Realtors selling—often expensive—homes in the area also don’t know much about debris flows and don’t present buyers with that information, or they’ll tell buyers that there was a flood a while ago, but the area is secure now. One realtor tells McPhee that “we would not have invested in these places if there was a problem” (253).

Carl Gunn arrived in Los Angeles in 1916 and worked afterward at a ranch. He’s now retired and says that most of the old-timer farmers have left the area. The newcomers are unaware of the dangers of the debris flows. McPhee takes a walk in the mountains with Chakib Sambar, who works as a vice-principal and immigrated to Los Angeles from Lebanon. Sambar owns a home in the area and chats about the risks of living there. McPhee also chats with Miner Harkness, who was born in the area and still lives there. Harkness comments on erosion in the Big Santa Anita Canyon caused by roads that humans paved for trucks to bring material to build crib structures or “check dams.” Harkness laments the destruction of the natural beauty due to erosion. Although engineers claim to be working to stop erosion in the area, Harkness critiques the Flood Control and the Army Corps of Engineers for their harmful—and costly—actions, namely, building roads and check dams that may have actually caused more debris flows. Harkness’s wife and baby were caught in a debris flow, though they escaped without injuries. McPhee asks Harkness whether he thought about leaving the area. Harkness says no.

McPhee provides statistics on the millions of cubic yards of debris caught in debris basins and reservoirs each year. The county expends $60 million each year to clean these basins and reservoirs. McPhee discusses how debris flows out of Little Anita Canyon and forms what are called alluvial fans in the San Gabriel mountains. Los Angeles takes responsibility for managing these alluvial fans and dumping the debris that collects in the basins. The city hires private truckers to haul this mud elsewhere. Mountain sand used to wash away to the ocean; now, with debris basins, the sand is instead hauled away. This loss of sand affects the quality of beaches in Los Angeles. Los Angeles must use trucks to manually move sand from the mountains to the beaches.

McPhee mentions that in the mountains Flood Control installed cloud-seeding generators, which shot silver iodide at clouds in order to enhance storms and bring more rainwater to Los Angeles. They wanted to increase rain, but they didn’t want to increase debris flows. The generators were shut down, however, after a severe storm. The big problem is that Los Angeles is running out places to deposit the debris. The passage of the California Environmental Quality Act has made it more difficult to find areas to dispose of debris due to potential harm to animals. The debris deposits also pose challenges to humans, as we see when McPhee cites the collapse of 40 houses that were built on disposed debris. Engineers dumped some of that debris back onto the mountain in a place called Burro Canyon at a cost of $20 million. McPhee and Wade Wells visit Burro Canyon, which has its own debris basins.