| This camp will take us north
through the Mojave Desert, Owens Valley, the Sierra Nevada,
and Mono Lake. You will see the evidence of plate tectonics,
glaciation and ice ages, volcanism, deposition, and weathering
and erosion.
Monday: We will leave school and
after dropping off the juniors and seniors and eating lunch,
we will have a short class session and then head for the
Mojave Desert.
On the way, we will stop at Boron to see
the Borax open Pit Mine, and take a tour of the processing
plant. You have already seen the video about how the Boron is
mined, what mineral forms it comes in, and how it is processed
and used.
The town of Boron
contains one of the world's largest borate mineral deposits.
The Kramer sodium borate ore body lies in the northwestern
portion of the Mojave desert, immediately north of the town of
Boron. The deposit derives its name from the mining district
in which it lies (Barnard & Kistler, 1976).
The Mojave Desert region
is shaped like a piece of pie; bounded on two sides by
earthquake faults. It is bounded by the San Andreas and
Garlock fault zones on the Southwest and north, but has no
definite eastern limits.
The Mojave block itself
is broken by many major but discontinuous faults. These appear
to be generally vertical to steep shear zones having
predominately lateral displacements of relatively small
amounts.
In the area of the boron
open pit mine, several faults crisscross the area from a
generally east to west direction, and rocks in this area may
be grouped into the three main divisions: (1) crystalline
rocks of pre-Tertiary age, (2) sedimentary and volcanic rocks
of Tertiary age, and (3) sediments and local basalt flows of
Quarternary age.
All the borate minerals
now mined from the western Mojave Desert are from the Kramer
borate deposit near Boron. In the mine area there is a clay
shale unit that is about 320 feet thick and is divisible into
three parts. In descending order these are (1) so-called
hanging-wall shale, 30-50 feet thick, containing scattered
borates, (2)middle or bluish-gray shale, 200-250 feet thick,
containing the sodium borate deposit known as the crystal body
or ore body, and a footwall shale, 25-30 feet thick,
containing minor borates.
The sodium borate ore
body is composed of semi-nodular layers, lenses, layers of
nodules or crystals, crystalline masses, and veinlets of
borate minerals in clay shale. The layers range from less than
a quarter of an inch to several inches thick.
The sodium borates
consist mainly of two minerals - native borax Na2B4O7 + 10
H2O; and Kernite, Na2B4O7 + 4 H2O. The borax is clear,
granular, noncleavable, ice like and commonly forms discrete,
subhedral to euherdral crystals 1/4 - 1 inch in diameter. The
Kernite is clear, cleavable in two directions to splintery
fragments and commonly forms very coarsely crystalline masses.
The borax occurs in the shallower part of the ore body, the
Kernite in the deeper part, regardless of stratigraphic
position. On exposure to air, even in the mines, borax soon
dehydrates to Tincalconite, Na2B4O7 + 5H2O, a white powdery
substance. Kernite also alters to Tincalconite, but very
slowly and indirectly through hydration to borax. Ulexite,
NaCaB5O9 + 6H2O, a white fibrous mineral, occurs in
comparatively minor amounts as thin fibrous layers and
veinlets.
The borate minerals in
the shale of the peripheral zone around the sodium borate ore
body are mainly Ulexite in the form of fibrous nodules,
layers, and veinlets, and Colemanite, Ca2B6O11 + 5 H2O, as
strata or lenses of coarse cleavable masses. These borate
minerals are locally abundant, but in most places are
scattered within the shale.
The sodium borate ore
body terminates rather abruptly at its margins, in a manner
that is not yet clearly understood.
The shale that contains
the borate minerals dips gently into the axis of a syncline
that passes eastward through the southern part of the ore
body. The ore body terminates southward against a fault and is
transected by several northwest-trending faults.
Depths from the surface
to the top of the ore body range from about 140 feet in the
northern and western parts to about 1,100 feet in the southern
part. The ore body of water-soluble sodium borate minerals is
apparently protected from solution by ground water by the
enclosing envelope of impervious shale, for the mines within
it are dry and the ore is unleached except along some faults
and the margins.
The borate minerals of
the Kramer district accumulated in a large desert lake in
which clays of the shale unit of the Tropico group were
deposited. The boron presumably came from the earth's interior
in solution, possibly in the form of boric acid, in thermal
waters that flowed from hot springs nearby. These springs
issued after eruption of the Saddleback Basalt, possibly from
or near fissures or vents through which the lava erupted. The
other unusual substances such as strontium, arsenic sulfides,
and other rare sulfides present in the borate deposits were
almost certainly brought up in hot spring deposits.
One theory for the
origin of the deposit is that borates presumably precipitated
as the thermal waters entered the lake and cooled, or as the
lake water became over-saturated. The calcium borates(ulexite
and colemanite), being the less soluble of the borate
minerals, would precipitate first near the margins of the
lake. The sodium borate minerals would then precipitate as the
water level receded and the water became saturated.
Kernite may have formed
from the dehydration of borax, in a low temperature
metamorphic reaction that left Kernite with a different
structure and less water attached in its molecular structure (Most
geology information taken from Dibble, 1967)
The earliest production
of borates from the western Mojave Desert region was in 1898
from a dry lake bed containing ulexite.
In a well drilled for
water in 1913 8 miles northwest of Kramer Station, Colemanite
was found at a depth of 370 feet. Exploratory drill holes
produced evidence that a large ore body of relative uniform
depth existed in the sub-surface. Shaft mining produced
colemanite in 1924. Upon further exploration, the Pacific
Coast Borax Company found borax and a new sodium borate named
Kernite. Two additional holes were drilled and were found to
contain borate minerals at a depth of 380 feet, and led to
large mine development. It was found that there was a huge
borate ore body triangular in shape.
The Kramer
borate deposit is now the major source of most of the borate
compounds produced in the U.S. as well as the world, although
a Turkish mine is making headway in the industry.
The open pit mine now
measures 6500 feet long, 4400 feet wide and 600 feet deep.
Sodium borate can be processed directly through separation and
refining. Kernite is first crushed, then mixed with water for
hydration, then put into piles where it converts into borax in
4-6 weeks. The calcium borates are being stockpiled as they
are more expensive to refine into borax, and with the large
amount of sodium borates still available, these will be
processed after the exhaustion of the ore body. In recent ore
mining outcrops, the ore is found to be 25% sodium borates and
12% calcium borates. Average processing costs are $35 per ton,
while borax sales are $200 per ton.
The open pit mine should
have no problem in continuing its mining well into the year
2000, due to the large amounts of deposits still existing in
the southeast corner of the mine.
After our stop at the Borax mine, we
will travel 30 miles west on highway 58 to Mojave, where we
will make a restroom stop and fuel up. From there we travel
north on highway 14 to Red Rock Canyon about 30 miles away.
This will be our camping spot for the night. We will use what
daylight we have left to set up camp, eat dinner and explore
the local area. Tomorrow we will spend the morning at Red Rock
Canyon.
Tuesday: After
breakfast, we will take about two hours to visit Red Rock
Canyon.
Red Rock Canyon is famous worldwide
for its "old west" look. Many westerns have been
filmed here over the years, including the TV series Bonanza.
Yet, the geology of Red Rock Canyon is even more impressive;
sedimentary layers give geologists a look into the past, and
the desert climate creates some impressive "badland"
type erosion. Badlands most commonly form in sedimentary
deposits soft enough to erode easily, but coherent enough to
stand in very steep faces. Desert thunderstorms let loose very
large drops, effective in producing threads, rills and gully
drainage patterns. This drainage system forms columns, spires,
chutes, and alcoves; color variation of the local rock include
white, cream, beige, brown, pink, red and green.
The main rock group in the park is the
Ricardo formation, named after the only human settlement to
remain for any length of time. Ricardo was either an innkeeper
there, a small boy who tended stagecoach horses, or a member
of the original family to settle there, the Hagars; no one
knows for sure. The Ricardo formation can be broken into two
sub-formations, the Cudahy and Dove Spring. Together, these
two total about 7,000 feet in thickness. In Red Rock Canyon,
only the Dove Spring formation is visible; the Cudahy
formation is exposed in Last Chance Canyon farther east. How
could sedimentary rock form to that thickness? The action of
the Garlock and San Andreas faults caused warping in the
region, causing a large basin to form called the El Paso. From
about 19 million years ago to less than 7 million years ago,
the basin has been filling with sediments. The basin sank
slowly, and as it sank, deposition occurred to keep the relief
fairly even.
From the south, Highway 14 makes a
dramatic entrance into the park. At the south face of the El
Paso Mountains, look for the El Paso fault (which is marked by
the front of the mountain range).
From the parking area (stop #1), look
north to see the first badland exposure. The Red Cliffs (named
for their color) display accordion like drainage. Look closer
to determine if the layers are horizontal or tilted.
Walking south across the parking area,
look at the top of the bluffs. A thick and massive layer of
tan to pink rock caps them. If you have time to inspect it
closely, you will find it is composed of a fine matrix of
consolidated volcanic ash (or tuff) which includes small
angular fragments of a variety of rocks, mostly volcanic. This
rock is called tuff breccia. It was deposited by a fast
moving, hot ash flow, erupted from a nearby volcano 12 to 13
million years ago. That volcano was on the south side of the
Garlock fault, which has since displaced the volcano many
miles to the east (what type of fault would that be?). If you
look down from the cliffs, you will see a small fault,
inclined to the east, that displaces the contact between the
tuff breccia and the underlying sedimentary beds by about 30
feet.
There are other geologically interesting
formations within the park, again showing the badland
topography and faulting.
We will leave Red Rock
Canyon and head north towards Bishop. On the way we will stop
at Coso Junction to eat lunch and view an impressive basalt
flow. The basalt was cut by glacial Owen River. At the head of
the flow is a dry waterfall and evidence of flowing water; the
rocks have been worn smooth. You will notice that the basalt
is full of holes, 1/4"-1/2" across. These were
formed by bubbles of gas in the molten material at the time of
flow. The last major discharge of the Owen River was during
the last minor ice age, 10-15 thousand years ago. The silt
laden water did a good job of eroding the basalt. Where do you
think the source of this basalt was?
We travel further north, and just past
the town of Olancha, Owens Lake comes into view. This once
large lake is now mostly dry, except for exceptionally wet
years. Since 1913, the flow of the Owen River that fed this
lake has been diverted to the aqueduct, shrinking the lake to
its present size. During the last ice age, the lake was 220
feet deep. Even before that, the lake suffered from a high
rate of evaporation, causing the water to be saline. Salts of
various sorts crystalize in lakes as these (similar to the
lake that was responsible for the great salt deposits in
Boron). Among the salts mined from this lake were Soda ash and
Boron.
Looming large to the
west is the Sierra Nevada range. We will study how this range
came into being later.
We will be stopping at
the north end of Owens Lake to view abandoned shoreline
markings.
To the west the Alabama
hills begin to rise (in front of the Sierras). These hills
formed by way of a Normal fault. We will discuss this further
at our next stop, which is a gravesite used to bury those
killed by the 1872 earthquake, one of the largest earthquakes
in historical times. This gravesite is located on an older
scarp caused by the down-dropping of the Owens Valley in
respect to the Sierras. In fact, the basement rock of Owens
Valley is 6000 feet below sea level, but sediments from the
Sierra Nevada and the White Mountains to the east have filled
the basin to its current level.
The scarp from the 1872 earthquake can
be seen 3/4 mile southwest of here. As we travel north, you
will see many scarps to the west of the highway, evidence of
the tectonic activity taking place here.
We will fuel up at Bishop, and continue
on highway 395 as it heads west. In a few miles, we start our
ascent towards Mammoth. This ascent is on what is called
Sherwin Grade, and takes place on the upper surface of the
Bishop tuff. Somewhere not too far to the north, about 700,000
years ago, volcanic vents repeatedly ejected clouds of hot
glowing ash and rock particles that spread out over a great
distance. These flows flowed by gravity, and they were kept
mobile by gases being released from the hot volcanic
fragments. When the material came to rest, it was still so hot
that the material partly recrystallized and fused, creating a
coherent rock called tuff.
When the eruptions ceased, it left a
nearly level sheet of material averaging 500 feet in
thickness. The sheet extends from Mono Lake south to Bishop, a
distance of 50 miles. It has since been deformed by faulting
and warping, and today it is being eroded so that only
remnants are preserved. The grade follows the largest remnant
remaining. The ascent we are taking was tilted by faulting.
As we drive, you can see what the Bishop
tuff looks like by observing the road cuts as we drive. When
fresh, this rock is mostly pink, but weathered exposures
appear brown.
Also look toward the south into the
canyons of the Sierras for signs of glaciation. Many of the
canyons in this area were carved by glaciers, with large
moraines deposited in or near the valley floor. Also look for
fault scarps that offset the moraines themselves.
As we near the top of Sherwin grade, you
will see a large lake to the north. This is Crowley Lake. It
is an artificial lake that lies on the south edge of Long
Valley (you’ll be hearing a lot about Long Valley during
this trip). Our campground is on the northwest side of the
lake. Dress warmly, it will get cold and it might be windy.
Wednesday: We will do some
mapping and sketching of geological features. Our first stop
will be Hot Creek, a place where hot springs have formed.
Hot Creek lies within a 10 by 20 mile
caldera called Long Valley, a product of a massive volcanic
eruption about 730,000 years ago. After the eruption, a lot of
molten rock was left behind under the surface, and through
weak spots in the lithosphere has leaked to the surface. These
"leaks" are the cause of all the cinder cones,
domes, craters and hot springs we will be seeing over the next
few days. The hills around Hot Creek are domes caused by
rising magma below the surface. Mammoth Mountain (to the west
from here) was also built up by rising magma. The heat source
of Hot Creek is from magma just a few miles below the earth’s
surface.
The future of Long Valley and Mono
Craters just to the north is uncertain. Geologists believe
that this area is the next one to erupt (second only to Mt.
St. Helens). Two important new studies by Dan Miller of the
USGS and Kerry Sieh of Cal Tech have predicted increased
volcanic activity in the area. Recent earthquake activity
seems to backup the theory that magma is once again making its
way to the surface. When this area does become active, it won’t
be from a single crater. This area historically erupts from
numerous vents stretching from Mono Lake southward to Crawley
Lake. Residents of the area are naturally concerned, as this
includes towns such as Mammoth Lakes and Lee Vining, not to
mention a large public-use recreational area. Historically,
this region erupts every few centuries, and since the first
eruption took place 600 years ago, the region appears to be
headed towards another active stage (Harris, 123).
From the parking lot, scan the horizon.
To the east is the White Mountains (+14,000). Looking north,
you can see the northern edge of the caldera marked by Glass
Mountain. To the west is Mammoth Mountain, while to the south
is Mt. Morrison (12,268 feet).
Hot Creek flows within a narrow gorge
cut deeply into the relatively soft volcanic rock of the Long
Valley Caldera. The rock cliffs are mostly rhyolite, but some
have been altered by hot water and volcanic gases (mostly
steam and carbon dioxide), along with some sulfur dioxide and
hydrogen sulfide (that’s the gross smelling stuff). The
sulfur oxide gases combine with the water to form sulfuric
acid, which is highly corrosive to rocks, vegetation and
geothermal pipes.
Many of the hot springs surround
themselves with siliceous sinter, a rock made of a form of
silica similar to opal, and travertine, a banded form of
calcite. These solids form when the hot water cools and loses
its gases, which causes the silica to precipitate. These
minerals also deposit in pipes, which makes the use of
geothermal energy difficult.
On your Hot Creek Map, you will be
splitting up into groups and mapping the locations where a)
there is current hot spring/fumarole activity and b) areas
that have been active in the past. CAUTION: Do not
climb over any fences. The areas near hot springs can be
treacherous and can collapse under your weight. The water in
the hot springs has been responsible for a few deaths over the
years, all caused by carelessness.
There has been a number of attempts to
use hot springs to produce electricity. Just north of Hot
Creek is the Casa Diablo Hot Springs Power Plant. Early
attempts at generating power failed for several reasons: the
steam is highly corrosive to pipes, drilling caused geothermal
activity to decrease, and the hot water that was brought up
polluted the groundwater due to boron and arsenic. A new plant
was dedicated in 1991, and uses a large building to condense
the steam into water to comply with environmental standards.
It produces 40 megawatts of electricity (enough for 10,000
homes).
Our next stop will be to Convict Lake.
We will be observing glacier depositional features, and
sketching the layers of rock that make up Mt. Morrison (if it
is free of snow). The mountain is made of Ordovician and
Silurian marine sediments. These sediments have been
overturned so that the older Ordovician sediments lie on top
of younger Silurian sediments.
All the way up the road leading to
Convict Lake are moraines made up of till. We will hike the
trail along the western edge of Convict Lake to see more
effects of glaciation.
We will be traveling into town tonight
for dinner, either at McDonald’s, Carl's Jr. or Shakey’s.
Thursday: This
is an exploration day throughout the Mammoth lakes/Long Valley
area. We will be traveling to Mono Lake and the Mono Craters,
exploring volcanism and the rock types associated with this
process (extrusive igneous). We will be mapping a number of
craters and lava flows throughout the day, looking for a
pattern in this geologically active area. Thursday:
This is an exploration day throughout the Mammoth lakes/Long
Valley area. We will be traveling to Mono Lake and the Mono
Craters, exploring volcanism and the rock types associated
with this process (extrusive igneous). We will be mapping a
number of craters and lava flows throughout the day, looking
for a pattern in this geologically active area. Thursday:
This is an exploration day throughout the Mammoth lakes/Long
Valley area. We will be traveling to Mono Lake and the Mono
Craters, exploring volcanism and the rock types associated
with this process (extrusive igneous). We will be mapping a
number of craters and lava flows throughout the day, looking
for a pattern in this geologically active area.
We will be taking a short loop around
June Lake, and study glaciation patterns in the area.
Next we will visit the Mono Craters.
Mono Craters is a collection of about 20 domes, extending in a
gentle arc to the south where they run into the Long Valley
caldera. They were formed during an active period of the
caldera dating back to 12,000 years ago, although some have
formed as recently as 1,800 years.
While on the south end of Mono lake, we
will also take a short hike down to the tufa towers. They were
formed at the openings of underwater springs by the
precipitation of minerals, usually calcium carbonate,
sometimes silica. They can only form underwater, which allow
us to imagine a former level of the lake. We will be doing
some field work here to attempt to determine the historic
shoreline of this once great lake.
If time permits we may also visit Bodie,
an old ghost town in the mountains north of Mono Lake. If we
go to Bodie, you will see one of the best preserved ghost
towns in California. The mines produced over $30 million of
gold and silver ores between 1876-1890. The ore was found in
veins caused by the upwelling of mineral rich water from deep
within in the earth which solidified as quartz veins.
Bakker, Elna S. An Island Called
California. Los Angeles: University of California Press,
1971.
Barnard, Ralph M., - Stratigraphical
and Structural Evolution of the Kramer Sodium Borate Ore Body,
Boron California.
Burgh, Dana Van, et al. How to Teach
with Topographic Maps. Arlington VA: NSTA, 1994.
Chronic, Halka. Pages of Stone -
Geology of Western National Parks and Monuments. Seattle:
The Mountaineers, 1986.
Clark, Ginny. Guide to Highway 395
Los Angeles to Reno. San Luis Obispo, CA: Western Trails
Publication, 1990.
Colemanite Deposits Near Kramer
Junction, San Bernardino County, CA, Special Publication
#50, 1976.
Dibble, Thomas W. Jr., Aerial Geology
of the Western Mojave Desert, California: U.S. Geol.
Survey Professional Paper #522, 1967.
Feather, Ralph M., Jr. Earth Science.
Westerville OH: Merrill, 1993
Fritz, William J. Roadside Geology of
the Yellowstone Country. Missoula, MT: Mountain Press,
1985.
Geologic Society of the Oregon Country. Roadside
Geology of the Eastern Sierra Region. Mono Lake Committee,
1982.
Harris, Stephen L. Agents of Chaos.
Missoula, MT: Mountain Press, 1990.
Harris, Stephen L. Fire Mountains of
the West: The Cascade and Mono Lake Volcanoes. Missoula,
MT: Mountain Press, 1988.
Pliocene Volcanic Rocks of the Coso
Range, Inyo County, California, USGS Professional Paper
#1383, 1986.
Sharp, Robert P., Geology Field Guide
to Southern California, Dubuque, IA: Kendall/Hunt, 1975.
U.S. Borax Public Relations Department, The
Story of Borax, 1969. |