Los Angeles Basin

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Los Angeles Basin

The second most populous city in the United States, Los Angeles has perhaps the most fascinating environmental history of any urban area in the country. The Los Angeles Basin, into which more than 80 communities of Los Angeles County are crowded, is a trough-shaped region bounded on three sides by the Santa Monica, Santa Susana, San Gabriel, San Bernadino, and Santa Ana Mountains. On its fourth side, the county looks out over the Pacific Ocean.

The earliest settlers arrived in the Basin in 1769 when Spaniard Gaspar de Portolá and his expedition set up camp along what is now known as the Los Angeles River. The site was eventually given the name El Pueblo de la Reyna de Los Angeles (the Town of the Queen of the Angels).

For the first century of its history, Los Angeles grew very slowly. Its population in 1835 was only 1,250. By the end of the century, however, the first signs of a new trend appeared. In response to the promises of sunshine, warm weather, and "easy living," immigrants from the East Coast began to arrive in the Basin. Its population more than quadrupled between 1880 and 1890, from 11,183 to 50,395.

The rush was on, and it has scarcely abated today. The metropolitan population grew from 102,000 in 1900 to 1,238,000 in 1930 to 3,997,000 in 1950 to 9,838,861 in 2000.

The pollution facing Los Angeles today results from a complex mix of natural factors and intense population growth . The first reports of Los Angeles's famous photochemical smog go back to 1542. The "many smokes" described by Juan Cabrillo in that year were not the same as today's smog , but they occurred because of geographic and climatic conditions that are responsible for modern environmental problems.

The Los Angeles Basin has one of the highest probabilities of experiencing thermal inversions of any area in the United States. An inversion is an atmospheric condition in which a layer of cold air becomes trapped beneath a layer of warm air. That situation is just the reverse of the most normal atmospheric condition in which a warm layer near the ground is covered by a cooler layer above it. The warm air has a tendency to rise, and the cool air has a tendency to sink. As a result, natural mixing occurs. In contrast, when a thermal inversion occurs, the denser cool air remains near the ground while the less dense air above it tends to stay there.

Smoke and other pollutants released into a thermal inversion are unable to rise upward and tend to be trapped in the cool lower layer. Furthermore, horizontal movements of air, which might clear out pollution in other areas, are blocked by the mountains surrounding LA county. The lingering haze of the "many smokes" described by Cabrillo could have been nothing more than the smoke from campfires trapped by inversions that must have existed even in 1542.

As population and industrial growth occurred in Los Angeles during the second half of the twentieth century, the amount of pollutants trapped in thermal inversions also grew. By the 1960s, Los Angeles had become a classic example of how modern cities were being choked by their own wastes.

The geographic location of the Los Angeles Basin contributes another factor to Los Angeles's special environmental problems. Sunlight warms the Basin for most of the year and attracts visitors and new residents. Solar energy fuels reactions between components of Los Angeles's polluted air, producing chemicals even more toxic than those from which they came. The complex mixture of noxious compounds produced in Los Angeles has been given the name smog, reflecting the combination of human (sm oke) and natural factors (fog ) that make it possible. Smog, also called ground level ozone , can cause a myriad of health problems including breathing difficulties, coughing, chest pains, and congestion. It may also exacerbate asthma , heart disease, and emphysema .

As Los Angeles grew in area and population, conditions which guaranteed a continuation of smog increased. The city and surrounding environs eventually grew to cover 400 square miles (1,036 square kilometers), a widespread community held together by freeways and cars. A major oil company bought the city's public transit system, then closed it down, ensuring the wide use of automobile transportation . Thus, gases produced by the combustion of gasoline added to the city's increasing pollution levels.

Los Angeles and the State of California have been battling air pollution for over 20 years. California now has some of the strictest emission standards of any state in the nation, and LA has begun to develop mass transit systems once again. For an area that has long depended on the automobile, however, the transition to public transportation has not been an easy one. But some measurable progress has been made in controlling ground level ozone. In 1976, smog was detectable at levels above the state standard acceptable average of 0.09 ppm a staggering 237 days out of the year. By 2001, the number had dropped to 121 days. Still, much work remains to be done; in 2000, 2001, and 2002 Los Angeles topped the American Lung Association's annual list of most ozone polluted cities and counties.

Another of Los Angeles's population-induced problems is its enormous demand for water. As early as 1900, it was apparent that the Basin's meager water resources would be inadequate to meet the needs of the growing urban area. The city turned its sights on the Owens Valley, 200 mi (322 km) to the northeast in the Sierra Nevada. After a lengthy dispute, the city won the right to tap the water resources of this distant valley. A 200-mile water diversion public works project, the Los Angeles Aqueduct, was completed in 1913.

This development did not satisfy the area's growing need for water, however, and in the 1930s, a second canal was built. This canal, the Colorado River Aqueduct, carries water from the Colorado River to Los Angeles over a distance of 444 mi (714 km). Even this proved to be inadequate, however, and the search for additional water sources has gone on almost without stop. In fact, one of the great ongoing debates in California is between legislators from Northern California, where the state's major water resources are located, and their counterparts from Southern California, where the majority of the state's people live. Since the latter contingent is larger in number, it has won many of the battles so far over distribution of the state's water resources.

Of course, Los Angeles has also experienced many of the same problems as urban areas in other parts of the world, regardless of its special geographical character. For example, the Basin was at one time a lush agricultural area, with some of the best soil and growing conditions found anywhere. From 1910 to 1950, Los Angeles County was the wealthiest agricultural region in the nation. But as urbanization progressed, more and more farmland was sacrificed for commercial and residential development. During the 1950s, an average of 3,000 acres (1,215 hectares) of farmland per day was taken out of production and converted to residential, commercial, industrial, or transportation use.

One of the mixed blessings faced by residents of the Los Angeles Basin is the existence of large oil reserves in the area. On the one hand, the oil and natural gas contained in these reserves is a valuable natural resource. On the other hand, the presence of working oil wells in the middle of a modern metropolitan area creates certain problems. One is aesthetic, as busy pumps in the midst of barren or scraggly land contrasts with sleek new glass and steel buildings.

Another petroleum-related difficulty is that of land subsidence . As oil and gas are removed from underground, land above it begins to sink. This phenomenon was first observed as early as 1937. Over the next two decades, subsidence had reached 16 ft (5 m) at the center of the Wilmington oil fields. Horizontal shifting of up to 9 ft (2.74 m) was also recorded.

Estimates of subsidence of up to 45 ft (14 m) spurred the county to begin remedial measures in the 1950s. These measures included the construction of levees to prevent seawater from flowing into the subsided area and the repressurizing of oil zones with water injection. These measures have been largely successful, at least to the present time, in halting the subsidence of the oil field.

Los Angeles' annual ritual of pumping and storing water into underground aquifers in anticipation of the long, dry summer season has also been responsible for elevation shifts in the region. Researchers with the United States Geological Survey (USGS) observed that the ground surface of a 20 by 40 km area of Los Angeles rises and falls approximately 1011 centimeters annually in conjunction with the water storage activities.

As if population growth itself were not enough, the Basin poses its own set of natural challenges to the community. For example, the area has a typical Mediterranean climate with long hot summers, and short winters with little rain. Summers are also the occasion of Santa Ana winds, severe windstorms in which hot air sweeps down out of the mountains and across the Basin. Urban and forest fires that originate during a Santa Ana wind not uncommonly go out of control causing enormous devastation to both human communities and the natural environment .

The Los Angeles Basin also sits within a short distance of one of the most famous fault systems in the world, the San Andreas Fault. Other minor faults spread out around Los Angeles on every side. Earthquakes are common in the Basin, and the most powerful earthquake in Southern California history struck Los Angeles in 1857 (8.25 magnitude). Sixty miles (97 kilometers) from the quake's epicenter, the tiny community of Los Angeles lost the military base at Fort Tejon although only two lives were lost in the disaster. Like San Franciscans, residents of the Los Angeles Basin live not wondering if another earthquake will occur, but only when "The Big One" will hit.

See also Air quality; Atmospheric inversion; Environmental Protection Agency (EPA); Mass transit; Oil drilling

[David E. Newton and Paula Anne Ford-Martin ]



Davis, Mike. Ecology of Fear: Los Angeles and the Imagination of Disaster. New York: Vintage Books, 1999.

Gumprecht, Blake. The Los Angeles River: Its Life, Death, and Possible Rebirth Baltimore: John Hopkins University Press, 2001.


Hecht, Jeff. "Finding Fault" New Scientist 171 (August 2001): 8.


American Lung Association. State of the Air 2002 Report. [cited July 9, 2002]. <http://www.stateoftheair.org>.

South Coast Air Quality Management District. Smog Levels. [cited July 9, 2002]. <http://ozone.aqmd.gov/smog>.

United States Geological Survey (USGS). Earthquake Hazards Program: Northern California. [cited July 9, 2002]. <http://quake.usgs.gov>.

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Los Angeles Basin

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Los Angeles Basin