America's Volcanic Past
|"Though few people in the United States may actually experience an erupting volcano, the evidence for earlier volcanism is preserved in many rocks of North America. Features seen in volcanic rocks only hours old are also present in ancient volcanic rocks, both at the surface and buried beneath younger deposits." -- Excerpt from: Brantley, 1994|
Volcanic Highlights and Features:
|[NOTE: This list is just a sample of various Nevada features or events and is by no means inclusive. All information presented here was gathered from other online websites and each excerpt is attributed back to the original source. Please use those sources in referencing any information on this webpage, and please visit those websites for more information on the Geology of Nevada.]|
The topography of the state is characterized by a patchwork of mountain ranges, which are commonly about 10 miles wide and rarely longer than 80 miles, and intervening valleys. The geologic structure that controls this basin-and-range topography is dominated by faults. Nearly every mountain range is bounded on at least one side by a fault that has been active, with large earthquakes, during the last 1.6 million years. For the last several million years, these faults have raised and occasionally tilted the mountains and lowered the basins. Over the years, these basins have filled with sediments that are derived from erosion of the mountains and that are tens of thousands of feet thick in some places.
continental margin, similar to the Atlantic coast of today,
persisted for hundreds of millions of
years before the more active, Pacific coast margin of today
began to take shape about 400 million
years ago. Repeated and prolonged periods of interactions
between the North American Plate and
oceanic plates to the west are recorded in the rocks
and expressed as folds, thrust faults, strike-slip
faults, normal faults, igneous intrusions,
volcanism, metamorphism, and sedimentary basins.
One of the most striking features of the generalized geologic map of Nevada is the
abundance of igneous rocks. Nevada rocks record volcanic and
intrusive igneous activity intermittently and repeatedly
from earliest geologic history to within the
last few thousand years. Some of Nevada's igneous rocks
are related to sea-floor spreading about
450 million years ago (much like the Mid-Atlantic Ridge or the East Pacific Rise today),
of ancient and modern plates, and hot spots in the
Earth's mantle and perhaps outer core (some
Nevada volcanic rocks can be correlated with the
Yellowstone hot spot, which, as a result of plate
tectonics, lay beneath southern Idaho and northern
Nevada producing volcanoes). Some of the
volcanic rocks in western Nevada represent the
precursor of the Cascades several million years
ago, and significant intrusions about 40, 100, and 160 million
years ago are probably linked to
similar plate-tectonic settings, whereby
tectonic plates of the Pacific Ocean were being subducted
beneath western North America.
Most, but not all, ore deposits in Nevada
are associated with igneous activity. In some cases,
metals came from the magmas themselves,
and in other cases, the magmas provided heat for
circulation of hot water that deposited metals
in veins and fractured sedimentary rocks. Some
spectacular mineral specimens occur in
ore deposits that formed when magmas intruded and
metamorphosed sedimentary rocks. Even today,
driven locally by deep circulation along faults and
locally by igneous activity, hot water
shows up in numerous geothermal areas. Nevada produces
approximately $100 million worth of
geothermally generated electric power annually, and
geothermal resources also are used for
agriculture, industrial applications, and space heating.
Excerpts from: Price, et.al., 1999, Geology of Nevada: Nevada Bureau of Mines and Geology Website, 2001
Basin and Range:9
The Columbia Plateau province is enveloped by one of the worlds largest accumulations of lava. Over 500,000 square kilometers of the Earth's surface is covered by it. The topography here is dominated by geologically young lava flows that inundated the countryside with amazing speed, all within the last 17 million years. Over 170,000 cubic kilometers of basaltic lava, known as the Columbia River basalts, covers the western part of the province. These tremendous flows erupted between 17-6 million years ago. Most of the lava flooded out in the first 1.5 million years -- an extraordinarily short time for such an outpouring of molten rock. It is difficult to conceive of the enormity of these eruptions. Basaltic lava erupts at no less than about 1100 degrees C. Basalt is a very fluid lava; it is likely that tongues of lava advanced at an average of 5 kilometers/hour -- faster than most animals can run. Whatever topography was present prior to the Columbia River Basalt eruptions was buried and smoothed over by flow upon flow of lava. Over 300 high-volume individual lava flows have been identified, along with countless smaller flows. Numerous linear vents, some over 150 kilometers long, show where lava erupted near the eastern edge of the Columbia River Basalts, but older vents were probably buried by younger flows.
Precambrian Rocks (older than 570 million years):7
Triassic Rocks (245 million to 208 million years ago):7
Jurassic Rocks (208 million to 144 million years ago:7
Cretaceous Period Rocks (144 million to 65 million years ago):7
Tertiary Rocks (65 million to 1.6 million years ago):7
Quaternary Rocks (1.6 million years to present):7
|Nevada's Volcanic Rocks|
Most spectacular mineral and rock specimens:7
Most spectacular mineral and rock specimens from Nevada are directly related to the igneous rocks and associated hydrothermal (hot water) ore deposits. These include the porphyry copper and molybdenum deposits (such as the Robinson district near Ely in White Pine County), skarns (including some of the abundant scheelite deposits -- skarns are types of contact metamorphic rocks that are directly associated with heat and hydrothermal fluids from magmas), different types of epithermal veins (such as the Comstock Lode and the ores at Goldfield), hot-spring deposits (such as those at Steamboat Springs in Washoe County), and Carlin-type ores (named for the Carlin Mine in Elko County). Many excellent mineral specimens can be found in the weathered and oxidized portions of ore deposits, and nearly every metallic mining district has some metal oxide minerals.
Easy Chair Crater, Nye County. Plagioclase feldspar, olivine, and clinopyroxene found within the basalt.
Cathedral Gorge is located in a long, narrow valley where erosion has carved dramatic and unique patterns in the soft bentonite clay. The park and visitor center is located just west of U.S. 93, two miles north of Panaca, Nevada.
Near Fallon in Churchill County, fossil fish are exposed in diatomite (diatomaceous earth) mines. The growth of diatoms, single-celled plants that comprise most of the rock diatomite, is promoted by volcanic activity that produced abundant quantities of silica, the chief ingredient of the diatoms.
Eldorado and Newberry Mountains, Clark County. Epidote, feldspar, fluorite, and quartz minerals found within cavities in the granite.
In Humboldt County precious opal occurs as a replacement of wood fragments in sediments with high contents of volcanic material. The silica needed to form the opal probably came from the silica-rich volcanic material in the sediments.
Ruby Mountains, Elko County. The mineral Beryl is found within the pegmatite. Incline Village, Washoe County. The minerals quartz and albite found within the pegmatite. Gillis Range, Mineral County. Topaz and amazonite found within the pegmatite.
Garnet Hill, near Ruth, White Pine County. Spessartine garnet found within the rhyolite.
Some rocks themselves are highly prized by collectors. An example is "wonderstone" (rock that is naturally stained with picturesque bands of red and orange iron oxide and hydroxide). In Nevada, some wonderstones are rhyolite lava flows, and some are sandstones. The wonderstone near Grimes Point in Churchill County, which is used in lapidary, is a rhyolite tuff that was altered by silica and pyrite from hydrothermal fluids.
Intrusive rock - granite, ash-flow tuff, rhyolite lava flows, domes
The basalt of Buckboard Mesa (2.8 million years ago) erupted in the northeast segment of the moat zone of Timber Mountain caldera. [See Timber Mountain Caldera below]
Buffalo Valley Volcanic Field:2
Monogenetic Volcanic Field; 15 kilometers length; 4-5 kilometers width; 1,420 to 1,750 meters elevation; eruptive history: 3.05 million years ago 920,000 years ago; olivine basalt composition. The Buffalo Valley volcanic field is located along the eastern margin of Buffalo Valley just north of the Fish Creek Mountains caldera (approximately 24 million years old). The field is comprised of 14 vents and associated flows. K-Ar dates from four flows within the field indicate that most of the cones and flows are early Pleistocene, although one flow yielded a later Pliocene age. The Buffalo Valley volcanic field is situated along the southeast margin of Buffalo Valley in north-central Nevada. The field is located approximately 235 kilometers east-northeast of Reno, Nevada, and approximately 5 kilometers southwest of Battle Mountain, Nevada. The field is accessible from Nevada State Highway 305 via a graded dirt road that runs along the northwest margin of the field.
Carson City is set between the Carson Range, (west), the Virginia Range, (north), and the Pine Nut Mountains (east). There is a slight complication to Carson City's location; Carson City is not located in Carson Valley! Carson Valley is the next valley to the south and is the location of the towns of Minden and Gardnerville. Carson City is in Eagle Valley, commemorating the site where one Frank Hall shot and killed an eagle in 1851.
Prison Hill Recreation Area:10
Approximately 2,450 acres known as Prison Hill Recreation Area have been set aside and dedicated as open space for the community of Carson City. This open space has a lot to offer those looking for a place to recreate. There is room to hike, bike, horseback ride, use off highway vehicles, experience views, enjoy the quiet and take some great pictures. Prison Hill is located on the southeast side of town and has three main community parking areas. [See Prison Hill Recreation Area below]
U.S. Highway 50:6
Near the crest of the hill, U.S. Highway 50 (east of Carson City, approximately 7 miles from Western Nevada Community College and one mile before the Lyon County Line) cuts through outcrops of black basaltic volcanic rock (relatively silica-poor rocks that tend not to erupt as violently as rhyolites). These rocks are closely related to the active extension (pulling apart) of the earth's crust in the Great Basin.
The Carson Range rises to the southwest of Reno, Nevada; it is the westernmost range in the Basin and Range physiographic province. It consists mainly of granitic intrusive igneous rock that crystallized at depth in the earth's crust about 70 million years ago and has been uplifted along a range-front fault system over the past several million years. The granite is overlain by andesitic volcanic rocks.
State Route 431:
Incline/Lake Tahoe Overlook:6
After carefully leaving the overlook parking area, continue down-grade to the west on State Route 431. For the first long section of grade beyond the rest area, you will be heading northwest and will have a view of the crest of the Carson Range between Rose Knob Peak, on the right, and Rose Knob, on the left. Note that the rocks on the crest have the same brownish outcrop color as the rocks capping Mount Rose to the east. These rocks are Pliocene and Miocene andesite and dacite volcanic flows that cap the lighter colored Cretaceous granitic rocks.
|Cathedral Gorge State Park|
Cathedral Gorge is located in a long, narrow valley where erosion has carved dramatic and unique patterns in the soft bentonite clay. The park and visitor center is located just west of U.S. 93, two miles north of Panaca, Nevada.
Clayton Valley Cinder Cone:2
The Clayton Valley cinder cone (1,405 to 1,490 elevation) is a solitary cone and flow at the northern end of Clayton Valley on the northeast piedmont of the Silver Peak Range. The closest major late Tertiary or Quaternary volcanic center, the 6.1 to 4.8 million years old Silver Peak caldera, is situated on the crest of the Silver Peak Range, approximately 25 kilometers to the southwest. However, the Clayton Valley cone does not appear to be genetically related to this caldera. The cone, approximately 85 meters high and 715 meters in diameter, is deeply breached on its east (downslope) side. The associated flow, originally at least 2 kilometers long and 1 kilometer wide, has been tentatively dated (on the basis of a single K-Ar analysis) at 390,000 years. The crest of this late middle Pleistocene cone is sharp, and its outer slopes have been superficially dissected by uniformly spaced, shallow gullies. The associated flow has been eroded by late Quaternary alluvial processes and partly buried by late Quaternary alluvium. Clayton Valley is in western Nevada, approximately 45 kilometers southwest of Tonopah, Nevada. The Clayton Valley cone lies just east of Nevada State Highway 265 at a point about 27 kilometers south of the junction of this highway with US 95. [See Silver Peak Caldera below]
A series of deeply dissected 3.7-million-year-old basalt scoria cones and lava flows are present in eastern Crater Flat. Four more basaltic centers (1.2 million years old) are aligned along a north-northeast trending arc in central Crater Flat. The youngest center in this area is the basalt of Lathrop Wells (100,000 to 10,000 years old), at the south end of Crater Flat. Crater Flat is a part of Timber Mountain volcanic center. [See Lathrop Wells and Timber Mountain Caldera below]
|Great Basin National Park|
Great Basin National Park:8
The "Great Basin" that Great Basin National Park is named after extends from the Sierra Nevada Range in California to the Wasatch Range in Utah, and from southern Oregon to southern Nevada. This is an area where no water drains to an ocean, but drains inward. As big as it is, the Great Basin is only part of an even larger region called the Basin and Range province that extends down into Mexico. The landscape around Great Basin National Park is a good example of what is found throughout the Basin and Range province - long mountain ranges separated by equally long, flat valleys.
Great Basin National Park encompasses most of the South Snake Range. The bulk of the rocks
exposed in this range are formed of sediments like sand, mud and limey ooze (silt and clay
particles mixed with calcium carbonate) that were laid down on the bottom of a shallow sea
during the late Precambrian and Cambrian (around 560 million years ago). As layers
accumulated upon layers, the sediments were turned into sedimentary rock. Sand lithified into
sandstone, mud into shale, and limey ooze into limestone.
The rocks in the park were further changed during a mountain-building
event that occurred around 200 million years ago during the
Mesozoic Era. This event, the Sevier Orogeny, pushed layers of
rock on top of each other, doubling the thickness of the crust. The layers at
the bottom of the stack were metamorphosed slightly - sandstone
changed gradually into quartzite, limestone to low-grade marble.
rose from deep within the Earth and pushed its way up into these
layers. It did not come to the surface, however. Staying underground, it
cooled to become granite. Where this hot magma was intruded, the
surrounding rock was metamorphosed slightly more.
After all of this activity, the region still did not
resemble the present landscape. The modern basins and
ranges began to appear only within the
last 30 million years or so, during the Cenozoic Era,
when the Earth's crust in this area began to stretch
in an east-west direction. Bedrock
nearest the surface reacted to the crustal stretching
by breaking into immense blocks several miles wide,
tens of miles long, and thousands of
feet thick. Many of these blocks fractured and the pieces
tilted and spread out like a row of odd-sized
books sliding out of place on a shelf.
The remnants of these broken blocks lie beneath the sediment
in the basins. Other blocks remained relatively intact and now form the
mountain ranges. Because stretching is in an east-west direction,
these ranges line up in a north-south direction.
The South Snake Range was
to see even more change. The younger unmetamorphosed layers of
rock on top of the range slid off of the older metamorphosed rocks in a
southeasterly direction, on a very low-angle fault line called a
decollement. This event makes the South Snake Range a metamorphic core
complex. The end of the Cenozoic Era witnessed more granitic
intrusions into the park, as well as
colder climates that further shaped the
|Grimes Point and Lake Lahontan|
Grimes Point Archaeological Site:6
Prehistoric natives scratched petroglyphs in boulders of andesite lava flows along the shores of the Pleistocene Lake Lahontan (a huge glacial lake that occupied much of the lower parts of northwestern Nevada and neighboring states during the Pleistocene Epoch until as recently as about 10,000 years ago). The boulders are coated with rock varnish, a thin layer of dark brown to black iron and manganese oxides. The U. S. Bureau of Land Management has constructed a path along which you can view the petroglyphs.
Grimes Point Wonderstone:6
Lake Lahontan reached its highest water levels at least four times between 75,000 and 10,000 years ago. We can see here abundant evidence for this lake, such as shorelines carved by wave action and sediments deposited in the lake. Look carefully in the gravels of the pit area for pebbles of Nevada wonderstone that were tumbled and polished by streams and by wave action along the shore of the lake about 13,000 years ago. This volcanic rock is a rhyolitic air-fall tuff, material ejected from a volcano about 12 million years ago. The rock was altered by hot waters that deposited pyrite (FeS2 ) and quartz (SiO2 ). Rainwater penetrated the rock and oxidized the pyrite to form liesegang bands of red hematite (Fe2 O3 ) and orange and brown goethite (FeO(OH)). Erosion broke pieces of the rock from its outcrop, and streams carried pebbles to the shore of Lake Lahontan. The hydrothermal fluids that initially altered the volcanic rock were much like waters in modern hot springs, which are common in Nevada. Such hot waters are used by geothermal power plants to produce electricity. Nevada annually produces about $110 million worth of electricity from geothermal power plants. This type of hydrothermal alteration is also commonly associated with the gold and silver deposits that have been so important to Nevada throughout its history.
A series of deeply dissected 3.7-million-year-old basalt scoria cones and lava flows are present in eastern Crater Flat. Four more basaltic centers (1.2 million years old) are aligned along a north-northeast trending arc in central Crater Flat. The youngest center in this area is the basalt of Lathrop Wells ... at the south end of Crater Flat. Crater Flat is a part of Timber Mountain volcanic center. [See Crater Flat above and Timber Mountain Caldera below]
The presence of basaltic ash in fissure fills (at Yucca Mountain) associated with fault zones aided in establishing the probable age of one of the major Quaternary surface-rupturing events; the ash is correlated with the eruption of the nearby Lathrop Wells volcanic center at 77±6 ka. ... The basaltic ash is correlated provisionally with tephra from the Lathrop Wells basaltic cone south of Yucca Mountain, which is dated by the 40Ar/39Ar method at about 77±6 ka (Heizler and others, 1999).
Lunar Crater Volcanic Field:2
The Lunar Crater volcanic field, an apparent middle to late Pliocene and Pleistocene continuation of the Reveille Range volcanic field immediately to the southwest, is superposed across the 25-million-year-old Lunar Lake caldera, a crudely circular topographic basin on the crest of the Pancake Range. The field contains approximately 95 late Pliocene and Pleistocene vents and at least 35 associated lava flows. Vents include cinder cones, elongate fissures, and at least two maars. Lunar Crater, a nearly circular maar, approximately 130 meters deep and 1,050 meters wide, is the most distinctive feature of the field. A second maar, approximately 550 meters wide and 65 meters deep, occurs at the south end of a northeast-trending chain of coalesced cinder cones. The Lunar Crater volcanic field is in the central Great Basin approximately 105 kilometers east-northeast of Tonopah, Nevada, and 140 kilometers southwest of Ely, Nevada. U. S. Highway 6 runs through the center of the Lunar Crater field and most areas of the field are readily accessible via graded dirt roads.
Lunar Crater - National Natural Landmark:12
Located 70 miles east-northeast of Tonopah in Nye County. A 400-acre depression that is thought to have been formed by a past volcanic explosion, and one of two maars in the volcanic field of the Pancake Range. Owner: Federal. DESIGNATION DATE: May 1973
For the most part, Peavine Peak is composed of the Peavine sequence, a pile of metamorphosed volcanic rocks of Mesozoic age (70 to 250 million years old). These rocks tell of a time when this area was similar geologically to the Cascades of Oregon and Washington today, with frequent volcanic eruptions due to a subducting tectonic plate to the west. The gold, copper, and iron deposits found on Peavine are the result of later hydrothermal activity that altered the volcanic rocks and formed veins of quartz and metallic minerals. Peavine Peak rose relative to the adjacent valleys along range-front faults that have been active over millions of years.
|Prison Hill Recreation Area|
Approximately 2,450 acres known as Prison Hill Recreation Area have been set aside and dedicated as open space for the community of Carson City. This open space has a lot to offer those looking for a place to recreate. There is room to hike, bike, horseback ride, use off highway vehicles, experience views, enjoy the quiet and take some great pictures. Prison Hill is located on the southeast side of town and has three main community parking areas. The geologic make-up of Prison Hill consists of two different rock types. Jurassic aged metamorphosed volcanic rock is exposed at the northern end, and a Cretaceous, medium-grained granitic rock exists at the southern end of the hill. In the northern end, as the larger rock mass disintegrates, pieces of broken outcrop appear that are dark-colored and consist of an andesite mud-flow breccia. Both rock types seem to be popular among local rock climbers and add interesting visual features to the hillsides.
Monogenetic Volcanic Field; 1,535 to 2,265 meters elevation; 45
kilometers length; 15-18 kilometers width; two principal periods of
activity: 6.2 to 5.3 million years ago, and 4.2 to 3.8 million years ago;
composition is predominantly alkali-olivine basalt and hawaiite.
The Reveille Range volcanic field contains approximately 50 vents and
associated lava flows within a north-south-trending zone, approximately 18
kilometers long, that is superposed across most of the length and width of
the range. Vents and flows are widely scattered within this zone and
cover a combined area of only approximately 140 square kilometers (about
17 percent of the total area of the zone). Flows range up to nearly 3
kilometers in width and 7 kilometers in length. Both vents and flows are
highly degraded. The loose tephra carapaces of most cones have been
largely eroded to reveal inner frameworks of dikes, sills, and agglutinate
layers. Flow surfaces are almost completely devoid of original surface
morphology and commonly are mantled by 1-4-meter-thick blankets of aeolian
silt and fine sand. The Reveille Range volcanic field is located in the
central Great Basin approximately 105 kilometers east-northeast of
Tonopah, Nevada, and 140 kilometers southwest of Ely, Nevada. Nevada State
Highway 25 runs along the north and west sides of the range, and the
northern and western parts are readily accessible via graded dirt roads.
Three or four flows of Quaternary age basaltic lava straddle the Nevada-Oregon border in an area relatively remote from other young volcanism. The flows (20-35 kilometers long) issued from small shield volcanoes. Only one isotopic age of 1.2 million years is available for the flows and little geologic mapping has been published. The lava flows are in the Charles Sheldon National Antelope Range, which is crossed by Highways 140, 34A, and 8A.
|Silver Peak Caldera|
Silver Peak Caldera:2
The Clayton Valley cinder cone (1,405 to 1,490 elevation) is a solitary cone and flow at the northern end of Clayton Valley on the northeast piedmont of the Silver Peak Range. The closest major late Tertiary or Quaternary volcanic center, the 6.1 to 4.8 million years old Silver Peak caldera, is situated on the crest of the Silver Peak Range, approximately 25 kilometers to the southwest. However, the Clayton Valley cone does not appear to be genetically related to this caldera. Clayton Valley is in western Nevada, approximately 45 kilometers southwest of Tonopah, Nevada. The Clayton Valley cone lies just east of Nevada State Highway 265 at a point about 27 kilometers south of the junction of this highway with US 95. [See Clayton Valley above]
Two Quaternary basalt centers occur at Sleeping Butte (300,000 to 10,000 years ago), 30 kilometers north of Beatty, Nevada, on the south flank of the Black Mountain caldera complex. Sleeping Butte is within the Timber Mountain volcanic center. [See Timber Mountain below]
|Soda Lake and Little Soda Lake|
Soda Lake and Little Soda Lake:6
Soda Lake and Little Soda Lake are two young volcanoes, younger than the sediments that were deposited in Lake Lahontan. Geologists call these types of volcanoes maars (pronounced "Mars"), so after this stop you can say that you "have been to maars." The maars are broad, low-relief, nearly circular volcanic craters. They probably formed when magma rose close to the surface, boiled the groundwater, and caused an explosive eruption of basaltic magma through the wet sediments of the lake basin. You can find telltale "basaltic bombs" around the margins of the craters. Look for small crystals of plagioclase feldspar (clear to white), olivine or peridot (green) or pyroxene (brownish black) in these dark vesicular volcanic rocks.
|Southwest Nevada Volcanic Field|
Southwest Nevada Volcanic Field:11
The southwestern Nevada volcanic field is in the southwestern Great Basin near and within several sensitive Federal facilities, including the Nevada Test Site, Yucca Mountain, and Nellis Air Force Base Range. The Great Basin, with its pronounced pattern of elongated mountain ranges and intervening basins, evolved as a result of regional crustal extension that took place during middle to late Cenozoic time. This extension represents the latter stages of a diverse history of tectonism, volcanism, and sedimentation, where younger events overprinted older events in ways that are sometimes difficult to unravel.
Development of the Volcanic Field:11
In Late Proterozoic and early Paleozoic time, nearly 5.5 kilometers of marine carbonate and clastic sediments were deposited on Proterozoic crystalline basement in the southwestern Nevada volcanic field region. An additional 2.5 kilometers of sediments were deposited during Devonian to Mississippian time, when marine sedimentation was intermixed with periods of major compressional tectonics throughout the Great Basin. In Late Cretaceous time, small granitic stocks intruded major thrust faults and related folds in Paleozoic sedimentary rocks. The thrust faults may be Mesozoic, or perhaps as old as Permian. In the early Tertiary, from 45 to 17 million years ago, while much of the rest of the Great Basin was experiencing widespread ash-flow eruptions and episodes of extension, the southwestern Nevada volcanic field region experienced minor volcanism and perhaps major episodes of tectonism. From 17 to 9 million years ago, the southwestern Nevada volcanic field developed as a result of episodic, voluminous magmatism and variably intense extension.
The first part of this tectonism predates the southwestern Nevada volcanic field, at perhaps 16 million years ago. Magmatism began at about 15.2 million years ago and culminated in voluminous rhyolite eruptions from a complex of large ash-flow calderas between 12.8 and 11.4 million years ago. After this period of intense volcanism, activity began to wane and change to bimodal rhyolite-basalt magmatism followed by entirely basaltic eruptions. From 9 million years ago to the present, volcanism and tectonism in the southwestern Nevada volcanic field have progressively declined.
Extent of the Field:11
The silicic ash-flow tuffs and lesser silicic and mafic lava flows of the southwestern Nevada volcanic field cover an area of more than 10,000 square kilometers and reach thicknesses of 4 kilometers or more in the center of the field. Each of the silicic ash-flow tuffs is associated with one or more calderas in the center of the volcanic field. Included within the area: Ammonia Tanks, Black Mountain, Buckboard Mesa, Bullfrog Hills, Calico Hills, Claim Canyon, Oasis Mountain, Pahute Mesa, Rainier Mesa, Silent Canyon caldera complex, Sleeping Butte, Thirsty Mountain, Timber Mountain caldera complex, and Yucca Mountain. [See Black Mountain above, Buckboard Mesa above, Timber Mountain below]
Much of the Steamboat Springs area is underlain by Cretaceous granodiorite. Pleistocene basaltic andesite flows cap the hills to the south of the main hot springs area. The hot-spring system formed in the early Pleistocene, prior to the eruption of the basaltic andesite flows. Steamboat Springs is an example of a present-day, active epithermal gold-silver hydrothermal system. The thermal area is on a line connecting several rhyolite domes located to the southeast and northeast, and it has been proposed that another rhyolite intrusion may underlie the hot-spring area. The source of energy for the thermal system is most probably the completely crystallized magma chamber from which the rhyolite domes were emplaced. The basaltic andesites have been dated at approximately 2.5 million years old and the rhyolite domes have been dated at 1.15 to 1.52 million years old. Thus, the hot-spring system has been active, possibly intermittently, for over 2.5 million years.
Steamboat Springs Domes:3
A small volcanic field of domes and flows occurs at the south end of Truckee Meadows from approximately 20 kilometers south-southwest of Reno, Nevada, to approximately 12 kilometers south-southeast of Reno, aligned along a northeasterly trend. The western dome is 3 kilometers south-southwest of Steamboat Hot Springs, a questionable dome underlies the hot springs, and four other domes are northeast of the springs. The southwest dome and one of the northeast domes are the largest, being one kilometer in diameter and nearly 150 meters in maximum relief.
State Route 431:
Incline/Lake Tahoe Overlook:6
After carefully leaving the overlook parking area, continue down-grade to the west on State Route 431. For the first long section of grade beyond the rest area, you will be heading northwest and will have a view of the crest of the Carson Range between Rose Knob Peak, on the right, and Rose Knob, on the left. Note that the rocks on the crest have the same brownish outcrop color as the rocks capping Mount Rose to the east. These rocks are Pliocene and Miocene andesite and dacite volcanic flows that cap the lighter colored Cretaceous granitic rocks. As you continue on down the grade, you will see small tongues of these flows exposed in road cuts. Where you see dark, greenish-gray rocks filling the gabions (the rock-filled wire structures securing the cuts above the road on the right), an andesite flow was cut at that point, and the rubble was put to use in the gabions.
Memorial Point Rest Area:6
This is a stop to view the lake shore, to test the water (with your hand, you may find the water a little cold for swimming), to check out the interpretive displays placed around the deck, and to use the rest rooms. Stairs lead down to the beach from both ends of the parking lot and from the deck, but please use caution as the stairs and trails can be slippery following seasonal storms. You will find this to be about the best view of the lake along this stretch of State Route 28. To the north is Incline Village, Sand Harbor is to the south, and to the west is a good view of the high Sierra crest. Particularly impressive at this location are the rounded granite outcrops and boulders that define the shoreline here.
Lake Tahoe State Park:6
Enjoy the view of the lake for the next several miles as you travel through Lake Tahoe State Park along the eastern shore of Lake Tahoe to Sand Harbor. If the light is right, you can easily see more of the rounded granite boulders on the lake bottom through the clear water. Sand Harbor Park, on the right, is a very popular Beyond Sand Harbor, you will see areas along the lake with more large granite boulders close to shore, screening small coves and inlets.
Timber Mountain Volcanic Field:1
Polygenetic volcanic centers; 1,065 to 1,675 meters elevation; Eruptive History - three episodes: 12 to 8.5 million years ago (waning stage of Timber Mountain caldera cycle), 9.0 to 6.5 million years ago, and 3.7 to less than 10,000 million years ago; Hawaiite to alkali basalt composition.
Late Cenozoic volcanic centers of the Timber Mountain volcanic field include spatially isolated small volume basaltic scoria cones and associated lava flows. Volcanic activity in this field switched from predominantly silicic to predominantly basaltic at about 10 million years ago. The volume of basalt eruptions declined drastically at approximately 8 million years ago, but small eruptions continued through 6.5 million years ago. Following a gap in activity, basaltic eruptions resumed at 3.7 million years ago, with a progressive decline in the volume through the Holocene. Since 3.7 million years ago, all basaltic centers have been in the southwest part of the volcanic field. There are three major occurrences of post-4-million-years-old basaltic activity in the Timber Mountain field: 1) Crater Flat, 2) Buckboard Mesa, and 3) Sleeping Butte. [See Crater Flat, Buckboard Mesa, and Sleeping Butte above]
Timber Mountain Caldera - National Natural Landmark:12
Nellis Air Force Gunnery Range and Nevada Test Site in Nye County. A restricted area containing a remnant of an elliptical caldera developed in the late Miocene and early Pliocene, it covers 8 to 10 miles and is surrounded by a moat-like depression extending to the rim of an older caldera. Owner: Federal. DESIGNATION DATE: May 1973
The Truckee originates at Lake Tahoe and ends at Pyramid Lake, about 40 miles to the northeast of Reno, Nevada. Along the Truckee River on the way to Fernley and in the mountains around Fallon are volcanic rocks that range in age from about 20 million years old to younger than 1 million years. Many of the older volcanic rocks are part of the same geologic phenomenon that produces volcanoes of the Cascade Mountains today. They include andesite (a kind of volcanic rock named for the volcanoes of the Andes Mountains) and rhyolite (a silica-rich volcanic rock that commonly erupts violently). White tuffs are evidence of some of the violent eruptions. Although there are some young rhyolites in the region (particularly near Mono Lake, California, and Steamboat Springs, just south of Reno), most of the younger volcanic rocks are basalts (relatively silica-poorer rocks that tend not to erupt as violently as rhyolites). These rocks are closely related to active extension (pulling apart) of the Earth's crust in the Great Basin.
From Carson City ... the crest of the Virginia Range is capped by red and black basaltic cinder deposits, which are mined to supply "lava rock" landscaping material for the surrounding area.
Northeast of Steamboat Springs:7
Rhyolite mined for aggregate.
Wilson Canyon is a popular Wildlife viewing site on Nevada State Route 208 south of Yerington. The highway follows a narrow, twisting canyon of volcanic cliffs alongside the West Fork of the Walker River. The site has sheer walls that provide crevices and ledges for the nests of white throated swifts, cliff swallows and rock wrens. Many raptors may be seen along the river corridor too.
1) Bruce M. Crowe, 1990, IN: Wood and Kienle
2) John Dohrerwend, 1990, IN: Wood and Kienle
3) Donale E. White, 1990, IN: Wood and Kienle
4) Charles A. Wood, 1990, IN: Wood and Kienle
5) USGS/NPS Geology in the Parks Website, 2001
6) Nevada Bureau of Mines and Geology Website, 2002
7) Price, et.al., 1999, Geology of Nevada: Nevada Bureau of Mines and Geology Website, 2001, University of Nevada, Reno, for publication in Rocks and Minerals Magazine, November 1999 issue
8) U.S. National Park Service, Great Basin National Park Website, 2002
9) USGS, A Tapestry of Time and Terrain Website, 2002
10) Nevada Bureau of Land Management Website, 2002
11) Grauch, Sawyer, Fridrich, and Hudson, 1998, Geophysical Framework of the Southwestern Nevada Volcanic Field and Hydrogeologic Implications: U.S. Geological Survey Professional Paper 1608
12) U.S. National Park Service, National Natural Landmarks Website, 2003
13) Keefer, W.R., Whitney, J.W., and Taylor, E.M., (eds.), Quaternary Paleoseismology and Stratigraphy of the Yucca Mountain Area, Nevada: U.S. Geological Survey Professional Paper 1689.
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