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Petaluma 12th Naval District Target No. 9
Petaluma, CA
generally rise to the high 50's in the early afternoon. The lowest recorded temperature
was measured at 24 degrees and occurred during the month of December.
The summer weather is dominated by a cool sea breeze resulting in an average summer
wind speed of nearly 15 mph. Winds are generally light in the early morning but
normally reach 20 to 25 mph in the afternoon. Wind gusts of up to 68 mph have been
observed.
Sea fog is another persistent feature of the summer weather. This high fog, occasionally
producing drizzle or mist, usually disappears during the late afternoon. Despite the
overcast mornings, summer days are sunny. On average, a total of only 14 days during
the four months from June through September are classified as cloudy.
Daytune temperatures are held down both by the overcast mornings and the strengthening
sea breezes in the afternoon. During the summer months occasional hot spells, lasting a
few days, are experienced without the usual high fog and sea breeze. The maximum
recorded temperature of 106 degrees was measured during the month of ~ une.~
3.3 GEOLOGYANDSOILS
3.3.1 Geology and Physiology
Petaluma is situated on the Coast Range's physiographic province of California, which is
characterized by northwest-trending mountains and valleys. Geomorphic features of the
local areas vary from low marshy land adjacent to the Petaluma River to more rugged
terrain to the east and west of the site where elevations reach 1,200 feet or more.
The oldest rocks exposed in Sonoma County occur at Bodega Head, west of the San
Andreas Fault. The granitic rocks found here represent the core of an ancient landmass
that once stretched southward and included what is now the Point Reyes Peninsula, the
Farallon Islands, and the granitic mountains of Santa Cruz and Monterey Counties.
These intrusive rocks were formed at great depths when they crystallized during the early
part of the Jurassic Period. Subsequent uplift brought them to the surface, and erosion has
reduced them to the isolated remnants seen today.
East of the San Andreas Fault are found somewhat contemporaneous marine sediments,
which were formed as geosynclinal deposits in an oceanic environment during the
Jurassic Period. These deposits, which together comprise the Franciscan Formation and
the Great Valley Sequence, are formed of sediments derived from an area located west of
the present shoreline. The area, which received these sediments was of broad extent and
was slowly subsiding.
During the 50 million years that the sediments were being deposited, they were intruded
with basic and ultrabasic rocks in the form of dikes, sills and pillow lava flows. Most of
Section 3 - Site Description
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