Southern California Geography

1
Southern California Geography

• Cismontane - this side of the mountains
• Coastal sides of Transverse and Peninsular Ranges
• Includes...
• Area 1/6 of the state
• Over 50 of population resides here

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Southern California Geography Mountains

• Two Mountain ranges of S. California
• 1) Transverse ranges
• aligned E-W (unusual alignment)
• Caused by Northward motion of Pacific plate along
  the San Andreas fault
• At contact point between Pacific plate and
  West-moving N. American plate, there is rotation
  on sub-plates, which act like ball bearings.

3
Transverse ranges

• Mountain Groups and highest peaks
• Santa Monica Mountains
• Sandstone Peak, 3111 ft.
• San Gabriel Mountains
• Mt. San Antonio (Baldy), 10,064 ft.
• San Bernardino Mountains
• Mt. San Gorgonio, 11,499 ft.

4
Peninsular ranges

• Santa Ana Mountains, Orange County
• Santiago Peak (Saddleback Mountain), 5,687 ft.
• San Jacinto Mountains, Riverside Co.
• San Jacinto 10,804 ft.
• Laguna Mountains, San Diego Co.
• Cuyamaca Peak, 6512 ft.
• Mountains of Baja California

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Southern California GeographyValleys

• Basins below mountains
• LA basin is a flood plain surrounded by mountains
• Series of N-S faults running under the flood
  plain
• Basins are drained by a series of rivers
• Los Angeles
• San Gabriel
• Santa Ana

6
Southern California Climate

• Product of Cold Ocean Water Latitude
• Combination of...
• Mediterranean Climate
• Long hot summers
• moderate winter precipitation
• Maritime Influence
• Gives a marine layer and a temperature inversion
  layer

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Mediterranean Climates

• pronounced seasonal changes in rainfall
• dry summer
• rainy winter
• little seasonal difference in temperature

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L.A. climate

• Average annual precipitation highly variable and
  terrain-dependent
• 12 in at ocean
• 25 in foothills
• 14.77 avg. for downtown Los Angeles
• Temperature--annual average
• high--75EF
• low -- 57EF

9
Weather in L.A. the Dry Season

• Weather dominated by Eastern Pacific high
  pressure area
• this high is a semi-permanent feature of the
  general hemispheric circulation
• Warm and very dry air descends from Pacific high
  pressure
• This air caps cool, ocean-modified air
• this is called an inversion
• produces a marine layer
• marine layer the prominent weather feature for
  much of year (late spring through early fall)

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Marine Layer

• Varies daily, due to variations in strength of
  Pacific high
• Thickens and advances inland during night and
  early morning
• Keeps moisture from evaporating by increasing
  relative humidity
• Retreats to ocean or burns off to hazy sunshine
  by midday.
• Surface pollutants trapped under marine inversion
  result in smog

11
Weather in L.A. the Wet Season

• Rainy season November--April
• Eastern Pacific high pressure ridge displaced to
  south
• L.A. on southern margins of polar jet stream
• When cold air is aloft, marine layer breaks down
• Lets Pacific storms push cold fronts across
  California
• 92 of our rainfall
• rainy season storms alternate with dry periods
• 10-30 individual storms per season
• Snow at high elevations

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Winter Storms in Southern California

• 1900-1943
• many storms hit S.California
• about same frequency as rest of state
• led to flood control measures (river
  channelization)
• 1943-1992
• extreme rainfalls only 5 times (14 statewide)
• BUT heavy rainfalls in 90s (92, 93, 95, 97,
  98)
• wettest decade since 1930s, 1940s

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• Most rain in 1 day
• 26.12 inches on slopes of Mount Wilson
• January 23, 1943
• Other big storms
• 2.60 in 1hr
• 1/4/95 in Long Beach
• 0.65 in 1 min.
• 4/3/26, north of Mount Wilson

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Temperature Patterns in Southern California

• Downtown L.A.
• average annual temperature 66.0E
• Daily maximums 67.7E January, 84.0E July
• Daily minimums 48.9E January, 63.3E July
• Record high 112E on June 26, 1990
• Record low 28Eon February 6, 1883, January 7,
  1913, January 4, 1949

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L.A. Average Annual Temperature 1877-1997
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Temperature change with distance from coast
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Wind Patterns in L.A.

• April-September
• light onshore winds (10-15 mph) develop due to
  Catalina Eddy, bring in marine layer
• October-January
• Santa Ana winds may blow (peak in December)
• Strong (gt 35 mph) downslope, dry winds
• gusts to 70-100 mph
• Caused by high pressure areas over Great Basin as
  cold air flows there from Canada
• May drive flames of intense fires

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Classification of Biological Communities

• California Communities
• Extreme range of climate and vegetation
• System devised by Munz and Keck in 1959 and is
  still in use
• Based on dominant plant species in each area
• Examples Joshua Tree Woodland and the Coastal
  Redwood Forest

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Southern California Seasons
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Southern California Communities

• Coastal Sage Scrub
• Chaparral
• Riparian Woodland
• Oak Woodland
• Montane forest
• Alpine tundra