Geoscience Reference
In-Depth Information
from streams draining the western foothills of the Sierra Nevada, the miners
turned to more intensive techniques to increase their yield. h e invention
of “hydraulic gold mining” allowed mining industries to get at the gold still
in the mountain rocks. Giant hoses blasted the western slopes of the Sierra
Nevada, eroding hillsides and generating large amounts of sediment.
Log dams were built to catch the debris in the streams before it reached
major rivers. During the fateful winter of 1861-62, the log dams failed, releas-
ing a huge pulse of sediment—boulders, cobbles, gravel, sands, and mud—
into the American, Yuba, and Feather rivers, where some of the worst l ood
devastation took place in the Sierra. h ese sediments made their way down-
stream to the Sacramento River, i lling the channel and thereby exacerbating
the l ooding in Sacramento. h e sediment pulse eventually made its way into
the Central Valley, delta, and San Francisco Bay.
Geologist G. K. Gilbert calculated that more than 1.5 billion cubic feet
of mining debris i lled the river systems before the practice of hydraulic
mining was outlawed in 1882 in the i rst federal environmental case in his-
tory. Unfortunately, the mining debris continued to aggravate l ooding in
these rivers for the rest of the nineteenth and into the twentieth centuries,
until it was i nally l ushed out of the system.
Out the Golden Gate
San Francisco Bay and its narrow outlet to the Pacii c Ocean at the Golden
Gate funnel all the rain and l oodwaters from most of Central and Northern
California. h at wet winter, a steady l ow of muddy, debris-laden water twenty
feet deep could be observed pouring through the San Francisco Bay and out
the Golden Gate for months. h e sheer mass of all this freshwater acted as a
wedge, pushing back Pacii c seawater and preventing it from entering the bay,
making the San Francisco Bay more like a freshwater lake. h e enormous vol-
umes of mud and silt carried by the turbulent waters into the bay i lled shallow
marshlands and caused a shoaling of the bay by up to three feet, causing the
expansion of marshlands into the estuary and completely wiping out the thriv-
ing oyster industry that had developed around the shores of the bay since 1850.
We can only speculate about what was washed down to San Francisco
Bay and out the Golden Gate during those epic l oods along with the muddy
waters: shredded homes, barns, trees, furniture and personal belongings,
even the remains of people and animals. All were carried out to the Pacii c
and a watery grave.
