The silver state. [volume] (Winnemucca, Nev.) 1909-1925, 1911-10-28
REPORT
ON PLACER MINES

which has been mined from the ter
tiary placer gravels of the Sierra Ne
vada is the subject of an exhaustive
report of WaIdemar Lindgren geolo-
gist, which has been issued by the
United States geological survey as pro-
fessionaI paper 70.
Studies by the geological survey on
the tertiary placer deposits of the
California Sierra began in 1886 and
were concluded about Is years later.
During this period % quadrangles were
geographically mapped and IA of these
were studied in geologic detail and
the results published by the survey in
geologic folios. Professional paper 73
includes the salient features of this
earlier work, most of which was ac-
complished by Mr.. Lindgren himself.
The report, thus comprehensive in geo.
graphic scope and the result of careful
studies, is believed to be the most
complete and thorough description of
great placer gold province ever pub
lished.
While in the main the report is a
detailed description of the entire area
covered, including these gold placer
gravels, Mr.. Lindgren s general ac-
count of the tremendous earth forces
which built up the Sierra, freed the
gold from its mother rock, and then
brought about its concentration in pre-
historic river channels is a most i'm
pressive description of continent build
ing. Looking backward through incon-
ceivable long vistas of time in which
periods covering millions of years sup
plant the centuries by which we now
compute its passage, the geologist pic
lures the uplift of the newborn noun
tain range by the forcing upward of
great bodies of molten granite. This
was closely followed by the introduc-
tion of veins and seams of goldbe
ing quartz. The resulting highland due
to this continental uplift was then
planed down by erosion in early
creataceous time-a geologic period
many thousands of years before the ad-
vent of man upon the earth.
Gold Concentrated in Prehistoric
Stream Beds.
/ After this erosion. and when the
mountains had reduced to gentle out
lines, deep rock decay took place and
much gold was released. Renewed up
! lift and the formation of sleeper
slopes resulted in greater erosion which
concentrated the loosened gold along
definite stream channels. During this
period of most active gold concentra-
tion, faulting and slipping of the rock
masses, with downthrow on the east
side of the Sierra had transformed an
approximately symmetrical mountain
range to one with steep easterly
slope
/ Tracing the long pathway Of this
early history the gologist now finds
that toward the end of what is known
as tertiary time-a comparatively re
cent geologic period-long quieseent
volcanic forces vigorously reasserted
themselves Rhyolite flows pouring
from many craters filled the valleys
covered with gold-bearing gravels,
deeply burying the gold, and new
stream courses were outlined in the
old valleys. Renewed disturbances
and eruptions began along the scarcely
healed eastern breaks of the Sierra,
rsulting in a westward fitting of the
main blocks of rock. This encouraged
deepr cutting by the streams, which
repeatedly crossed their old courses,
so that now the concentration of gold
proceeded under less favorable torren-
! tial conditions. At this time volcanic
vents were opened along the crest of
the Sierra. many of them sending
forth immense volumes of lavas, ashes
and mud. These great flows filed
many of the valleys to their rims and
converted almost the whole of the
northern Sierra into desolate steam
ing mass of volcanic mud. Storm wa
ters now began the canyon-cutting
epoch, amazing in its results as we see
them today. Tn many places the old
rivers of tertiary time were exposed,
and cross sections of their valleys are
now seen on the steep canyon slopes,
many of them high above the present
river beds; but large stretches of the
old river channels remain blanketed
beneath a thousand feet or more of
volcanic mud, now hardened into rock.
The Advent Of Gold Hunters.
The geologic events thus outlined
were followed by the happenings of
of gold seekers invaded the Sierra.
They worked first along the present
streams, but gradually the metal was
traced to old tertiary river beds on
the SUBMITS of the ridges and to the
quartz veins, the primary source of
all gold in the Sierra Nevada. Mil
lions of dollars were produced annually
up to the seventies of the last cen
tury, but since that time, owing to the
prohibition of hydraulic mining and
the gradual exhaustion of the richer
channels suitable for drift mining, the
industry has slowly diminished until
now less than $1,000,00o is produced
annually. Mr.. Lindgren says: "Gold
is still contained in the tertiary chan
nels: miles of them are still unworked,
but the problems are how to extract
it without damage to other property
from the debris and how to reduce the
cost of drift mining so as to permit
he exploitation of the less remunera
tive deep gravels.'
In this connection Mr. Lindgren has
traced the old channels, and accurate
maps accompanying his report show
in detail the restoration fo the ter
tiarv drainage lines.
Dredging Industry Takes the Place os