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and there, however, isolated hills or elevated mesas, projecting 
above the talus, remain as indicators of the original sedimentary 
deposits. This large interior valley is separated from the low 
valley along the coast of Los Angeles and Orange Counties by 
the Santa Ana Mountains, and a series of low hills which connect 
them with the Santa Monica Mountains. North of this last 
range is the low coastal valley of Ventura County, the only 
other valley of any considerable area on the western side of the 
mountains. 
CLIMATOLOGY 
GENERAL DEscRIPTION 
There is great diversity of climate, due principally to topography, 
a factor which exerts a marked influence in southern California, 
since the principal mountain ranges lie transversely to the path 
of the prevailing winds and storms. Asa rule, however, the climate 
is one of scant precipitation and high temperatures, conditions 
that become more and more pronounced toward the interior, away 
from the ameliorating influences of the cool moist sea-breeze. ‘The 
rainfall is chiefly confined to the winter and early spring months, 
the dry summer and autumn having almost continual sunshine. 
Precipitation is greatest in the mountains, with an average annual 
rainfall in some localities exceeding 100 centimeters, and least in 
the Colorado Desert, where it is less than 5 centimeters in some 
sections. Fully as great extremes are found in temperatures. 
On a winter day, for instance, one may stand among blooming 
roses or in orange groves laden with ripe fruit, and watch the 
snow, driven by piercing winds, drifting about the rugged peaks 
of the neighboring mountains. 
The following temperature and rainfall records have been 
compiled from McAdie’s “Climatology of California’: 
