Los Angeles is irregularly shaped and covers a total area of 498.3 square miles (1,291 km2), comprising 469.1 square miles (1,215 km2) of land and 29.2 square miles (76 km2) of water. The city extends for 44 miles (71 km) longitudinally and for 29 miles (47 km) latitudinally. The perimeter of the city is 342 miles (550 km). It is the only major city in the United States bisected by a mountain range.
Los Angeles is both flat and hilly. The highest point in the city is 5,080 ft (1,550 m) Mount Lukens, located at the northeastern end of the San Fernando Valley. The hilly parts of Los Angeles include the entire Santa Monica Mountains which stretch from Downtown to the Pacific Ocean, the Mt. Washington area north of Downtown, eastern parts such as Boyle Heights, the Crenshaw district around the Baldwin Hills, and the San Pedro district.
The Los Angeles River, a major river which is largely seasonal, is the primary drainage channel. It was straightened and lined in concrete by the Army Corps of Engineers for almost its entire length to act as a flood control channel. The river begins in the Canoga Park district of the city and flows east from the San Fernando Valley along the north edge of the Santa Monica Mountains as they diminish, then south through the city center, then through nearby Vernon on its way to its mouth in the Port of Long Beach at the Pacific Ocean.
Los Angeles is subject to earthquakes due to its location on the Pacific Ring of Fire. The geologic instability has produced numerous faults, which cause approximately 10,000 earthquakes annually. One of the major faults is the San Andreas Fault. Located at the boundary between the Pacific Plate and the North American Plate, it is predicted to be the source of Southern California's next big earthquake. Major earthquakes to have hit the Los Angeles area include the 1994 Northridge earthquake, the 1987 Whittier Narrows earthquake, the 1971 San Fernando earthquake near Sylmar, and the 1933 Long Beach earthquake. Nevertheless, all but a few quakes are of low intensity and are not felt. The most recent earthquake felt was the 4.4 2010 Pico Rivera earthquake on March 16, 2010. Parts of the city are also vulnerable to Pacific Ocean tsunamis; harbor areas were damaged by waves from the Valdivia earthquake in 1960. The Los Angeles basin and metropolitan area are also at risk from blind thrust earthquakes.
Los Angeles has a Subtropical-Mediterranean climate (Köppen climate classification Csb on the coast, Csa inland), and receives just enough annual precipitation to avoid Köppen's BSh (semi-arid climate) classification. Los Angeles enjoys plenty of sunshine throughout the year, with an average of only 35 days with measurable precipitation annually.
The average annual temperature in downtown is 66 °F (19 °C): 75 °F (24 °C) during the day and 57 °F (14 °C) at night. In the coldest month, January, the temperature typically ranges from 59 to 73 °F (15 to 23 °C) during the day and 45 to 55 °F (7 to 13 °C) at night. In the warmest month – August – the temperature typically ranges from 79 to 90 °F (26 to 32 °C) during the day and around 64 °F (18 °C) at night. Temperatures exceed 90 °F (32 °C) on a dozen or so days in the year, from one day a month in April, May, June and November to three days a month in July, August, October and to five days in September. Temperatures are subject to substantial daily swings; in inland areas the difference between the average daily low and the average daily high is over 30 °F (17 °C). Average annual temperature of sea is63 °F (17 °C), from 58 °F (14 °C) in January to 68 °F (20 °C) in August. Sunshine hours is above 3,000 per year, from average 7 hours of sunshine / day in December to average 12 hours of sunshine / day in July.
The Los Angeles area is also subject to phenomena typical of a microclimate. As such, the temperatures can vary as much as 36 °F (20 °C) between inland areas and the coast. California also has a weather phenomenon called "June Gloom or May Grey", which sometimes gives overcast or foggy skies in the morning at the coast, but usually gives sunny skies by noon, during late spring and early summer.
Downtown Los Angeles averages 15.14 inches (384.6 mm) of precipitation annually, which mainly occurs during the winter and spring (November through April) with generally moderate rain showers, but usually as heavy rainfall and thunderstorms during Winter storms. The coast gets slightly less rainfall, while the mountains get slightly more. However the San Fernando Valley Region of Los Angeles can get between 16 and 20 inches of rain per year. Years of average rainfall are rare; the usual pattern is bimodal, with a short string of dry years (perhaps 7–8 inches/180–200 millimetres) followed by one or two wet years that make up the average. Snowfall is extremely rare in the city basin, but the mountains within city limits typically receive snowfall every winter. The greatest snowfall recorded in downtown Los Angeles was 2 inches (5 cm) in 1932. The highest recorded temperature in downtown Los Angeles is 113 °F (45 °C) on September 27, 2010 and the lowest recorded temperature is 24 °F(−4 °C) on December 22, 1944.
The Los Angeles area is rich in native plant species due in part to a diversity in habitats, including beaches, wetlands, and mountains. The most prevalent botanical environment is coastal sage scrub, which covers the hillsides in combustible chaparral. Native plants include: California poppy, matilija poppy, toyon, Coast Live Oak, and Giant Wildrye. Many of these native species, such as the Los Angeles sunflower, have become so rare as to be considered endangered. Though they are not native to the area, the official tree of Los Angeles is the Coral Tree (Erythrina caffra) and the official flower of Los Angeles is the Bird of Paradise (Strelitzia reginae).Mexican Fan Palms, California Fan Palms, and Canary Island Palms can be seen throughout the Los Angeles area, despite the latter being non-indeginous to Southern California.
The name given by the Chumash tribe of Native Americans for the area now known as Los Angeles translates to "the valley of smoke" because of the smog from native campfires. Owing to geography, heavy reliance on automobiles, and the Los Angeles/Long Beach port complex, Los Angeles suffers from air pollution in the form of smog. The Los Angeles Basin and the San Fernando Valley are susceptible to atmospheric inversion, which holds in the exhausts from road vehicles, airplanes, locomotives, shipping, manufacturing, and other sources. The smog season lasts from May to October.Unlike other large cities that rely on rain to clear smog, Los Angeles gets only 15 inches (380 mm) of rain each year: pollution accumulates over many consecutive days. Issues of air quality in Los Angeles and other major cities led to the passage of early national environmental legislation, including the Clean Air Act. More recently, the state of California has led the nation in working to limit pollution by mandating low-emission vehicles. Smog should continue to drop in the coming years due to aggressive steps to reduce it, electric and hybrid cars, improvements in mass transit, and other pollution reducing measures.
As a result, pollution levels have dropped in recent decades. The number of Stage 1 smog alerts has declined from over 100 per year in the 1970s to almost zero in the new millennium. Despite improvement, the 2006 and 2007 annual reports of the American Lung Association ranked the city as the most polluted in the country with short-term particle pollution and year-round particle pollution. In 2008, the city was ranked the second most polluted and again had the highest year-round particulate pollution. In addition, the groundwater is increasingly threatened by MTBE from gas stations and perchlorate from rocket fuel. With pollution still a significant problem, the city continues to take aggressive steps to improve air and water conditions. The city has met its goal of providing 20 percent of the city's power from renewable sources in 2010.