Journeys Around Lake Tahoe

By Rich Schweickert

Lake Tahoe, a national treasure, is one of the most popular vacation destinations in the United States. This book, based on over 25 years' research by the author and collaborators, reveals the geologic story behind Tahoe's magnificent scenery and landscapes; guides the visitor on journeys (day trips) around the lake on all routes in the Tahoe basin; and blends in important details of scenery, geology, and history.
The first five chapters describe what travelers can see or learn driving near and around the lake and links magnificent sites where they can hike, bike, ski, swim, or drive to major geological themes. There are many new insights on world-famous locations including Emerald Bay, Cave Rock, Stateline Point, and South Lake Tahoe. Revelations from underwater geology, about which most people know very little, present the Tahoe Tsunami as a central theme as well. Brief, bullet-point summaries illustrate that Lake Tahoe is part of a much greater historical milieu that includes the "ancient ones" (the Washoe people), in addition to "Anglo" history. Few visitors are aware of the historical connections or how "Anglos" have done much to destroy Lake Tahoe, while dedicated public and private groups are even now trying to restore and protect Tahoe's magnificence from our own abuses.
The Tahoe basin and Virginia City had major impacts on each other, and together they greatly influenced U.S. history. Timber and fuel wood from Tahoe's once-pristine forests (which were nearly destroyed) contributed to the deep Comstock mines, which produced great amounts of silver and gold. The mineral wealth led to Nevada Statehood, contributed to the Union victory in the Civil War, led to development of San Francisco and its great fortunes, influenced the routing of the transcontinental railroad, led to establishment of Mackay School of Mines, and so on. Virginia City is revealed by driving through and walking around the town, and by describing some of the most important deep mines.
Countless excellent Lake Tahoe books have been published, but most are to be read at home and have pretty pictures with little discussion. Certain "guides" list places to stay, shop, eat, and gamble or places to camp, swim, hike or ski. This book, which can also be enjoyed at home, uses numerous color photos and maps to guide the traveler or explorer on day trips around all the routes in the Tahoe basin, and reveals that every viewpoint has an important story to tell. Photography is by the author, except where noted.

• Language: English
• Publisher: BookBaby
• Release date: Jun 17, 2024
• ISBN: 9798350959895

Rich Schweickert

Rich Schweickert is a passionate naturalist and photographer who resides in Reno, Nevada. After his Ph. D. at Stanford University in 1972, he was a Professor of Geology at Columbia University and Lamont-Doherty Geological Observatory, New York before moving to Nevada and serving over 25 years as Professor of Geology at University of Nevada, Reno (UNR). Rich has done extensive research at Lake Tahoe in collaboration with many other earth scientists and students. His Tahoe research involved ~465 field days and hiking all peaks around the basin, walking all beaches, and many boat days logging over 100 ROV dives. He has carried out comparative studies in the eastern Sierra Nevada, Austrian, French, Italian, and Swiss Alps, Scotland, Alaska, British Columbia, Alberta, Montana, Chile, Argentina, and Antarctica. With over 200 publications, he has made numerous presentations on Tahoe geology to public groups and State and Federal agencies.

Book preview

CHAPTER 1--Lake Tahoe, a national treasure

see Chapter 1 of Journeys Across Nevada’s Wild Lands (2020)

for basic geologic principles and perspectives on geologic history

FRONTISPIECE

Lake Tahoe, a national treasure. All the superlatives have been used to describe this legendary place, including James’s 1915 words, a sublime beauty, all seasons, and lake of the sky. …Lake Tahoe so exquisitely mirrors the purity of the sky…. The lake shines with its crystalline waters shimmering in the breeze (Photo 1-1). In this lake, color variation is immense; James described colors of inky blue, sapphire blue, ultramarine, amethystine, emerald green, and jade. To these we may add aqua and aquamarine (not to mention brilliant colors of spectacular sunsets!). And the lake has truly grand scenery with surrounding majestic peaks (Photos 1-1, 1-2). In 1872 Mark Twain pronounced it the fairest picture the whole earth affords.

Photo 1-1. Lake Tahoe shines in all seasons and reflects mountains, snowy ridges, and canyons. Clockwise from upper left: View west near Camp Richardson; view south near Baldwin Beach; view north toward Sand Harbor; view west at Blackwood Canyon.

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Lindé Ravizé, a modern poet, in Hearts of Light, one of the greatest books ever published on Lake Tahoe, said it best:

"Clearer than a crystal glass,

yet purer than the sky.

No matter what may come to pass,

refreshment for the eye.

Soothing to the soul at rest,

and calmer than the sea.

Waters that attune the best

of perfect harmony.

No other place on Mother Earth

bears such an air of grace,

reflections of its vernal birth

surround this sacred place…."

and,

"Vivid turquoise, emerald green,

polished with a diamond sheen…

since ancient times it has been seen

as mirror of the sky.

Vastly blue yet crystal clear,

a strong imposing sapphire tier,

reflecting pool of mountains near…

a jewel to the eye……"

(excerpted from Ravizé and Ravizé, 1999, Hearts of Light, pp. 16 and 23).

Photo 1-2A. Magnificent Emerald Bay after winter snow. Image from Ravizé and Ravizé (1999) with permission.

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Photo 1-2B. Selected Tahoe scenes. Clockwise from upper left: View east across Emerald Bay, west shore (Chapter 5); view north along east shore (Chapter 4); sunset view southeast from Tahoe Vista, north shore (Chapter 3); view south along eastern shoreline from Incline Overlook (Chapter 4); view north at Sand Harbor and Rose Knob Ridge, east shore (Chapter 4); sunset view northwest from Ski Run Marina, south shore (Chapter 2).

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A modern concept, blue therapy,

…being in or near blue spaces such as rivers, lakes and the sea boosts our emotional wellbeing. Spending time in blue spaces lowers the risk of stress, anxiety, obesity, cardiovascular disease and premature death--F. Adkins and K. Latham, BBC Future, 11/8/2022

echoes many of the Tahoe values of nature writers. Part of Tahoe’s magic has to do with its shallow, sandy nearshore areas viewed through crystalline blue waters.

Sadly, Tahoe’s clarity has declined over the past 55 years, and major efforts have been underway by scientists and management groups for decades to improve the clarity. From secchi disk studies by U.C. Davis scientists (recording the maximum depth at which a 10-in diameter white disk can be seen from the surface), Tahoe’s clarity, about 100 feet in 1968, is only about 63 feet in 2022-23. This loss of clarity is attributed to a number of factors including increases in fine particulate matter (from soils, sediment, and algae) and severe climate events. However, a 2018 EPA report on over 1,100 U.S. lakes indicates a secchi depth of about 16 feet (~4.8 m) is exceptional. Thus, Tahoe’s clarity still is far greater than that of almost every other lake in the U.S.!

Figure 1. Secchi disk data published in 2022 by Tahoe Environmental Research Center (TERC), U.C. Davis. This shows the successes of massive federal funding for environmental restoration. Prior to 1997, when new federal funding began, the rate of loss of clarity over 30 years averaged about 10.3 inches/year. Since 1997, with the help of generous federal funding, the clarity over 25 years has remained fairly stable and the rate of clarity loss has averaged about 2.7 inches/year, a 3.8-fold reduction! In 2023, TERC announced a year’s secchi depth of 72 feet, the best reading in years.

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To comprehend the grandeur of Lake Tahoe, we must explore the lake and its basin. Beach scenes and their color palettes are the first places to seek out (Photo 1-3).

Photo 1-3. Beach scenes at Lake Tahoe display the color palette. Abbreviations: E--east shore; NLT--north shore; SLT--south shore; SW--southwestern shore; W--west shore. Baldwin, Connolley, Zephyr Cove, and Lakeside beaches are in Chapter 2. Tahoe Vista beach is in Chapter 3. Incline, Skunk Harbor, and Sand Harbor beaches are in Chapter 4. Camp Richardson, Meeks, Rubicon Bay, and Emerald Bay beaches are in Chapter 5.

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Adding to the appeal of the crystalline blue waters, grand beaches, and dramatic scenery, magnificent hiking and mountain biking routes surround the lake (Photo 1-4). These include the East shore bikeway, proclaimed America’s most beautiful bikeway. The Tahoe Rim trail, almost 175 miles in length, encircles the basin. Segments of the trail include, going clockwise,

North Tahoe

Tahoe City to Brockway Summit--22.1 miles,

Brockway Summit to Mt. Rose Summit/Tahoe Meadows--20.2 mi,

East Tahoe

Tahoe Meadows to Spooner Summit--24.1 mi,

Spooner Summit to Kingsbury--19.0 mi,

South Tahoe

Kingsbury to Big Meadow--22.9 mi,

Big Meadow to Echo Lakes--18.3 mi,

West Tahoe

Echo Lakes to Barker Pass--32.5 mi,

Barker Pass to Tahoe City--16.4 mi.

Photo 1-4. Views from some of Tahoe’s magnificent hiking trails. Several shown are parts of the Tahoe Rim trail. Monument Peak trail is in Chapter 2. Eagle Rock, Ellis Peak, and Stanford Rock trails are in Chapter 3. Flume, Genoa Peak and Stateline Point trails, and Tahoe East Shore bikeway are in Chapter 4. Cascade Falls and Maggies Peaks trails are in Chapter 5.

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In addition to beaches and hiking and biking trails, world-class skiing (including Palisades Tahoe, Homewood Mountain Resort, Heavenly Mountain Resort, Diamond Peak, Mt. Rose-Ski Tahoe, and Northstar), charming mountain towns, boating, kayaking, swimming, diving, snorkeling, and river rafting, all beckon to the traveler. Countless online resources provide excellent guides to these activities. Chapters in this book explore many of these gems.

Some Lake Tahoe Facts (see also Chapters 2 and 4)

The Lake Tahoe basin, which lies within the Basin and Range province

-is a normal-fault-bound depression

-known as an asymmetric half-graben (Cross-section 1-1)

-Crystal Bay is a smaller half-graben nested within the larger Lake Tahoe half-graben.

Cross-section 1-1. This simplified west-to-east cross-section drawn across the middle of Lake Tahoe (modified from Schweickert et al., 2004) shows how the Lake Tahoe basin formed by slip along several east-dipping normal faults--some labelled here. This structure is called a half-graben. Note how the southern part of the Carson Range and the Sierra Nevada both have been tilted to the west. Colors and patterns: Pink with dashes--Cretaceous granite of Sierra Nevada batholith; bright pink--23 m.y. ash-flow tuff in a paleovalley; gold with parallel lines--Miocene to Pliocene andesite flows and breccias; gray--glacial moraines; yellow with parallel lines--Pleistocene to Recent lake sediments. The volcanic rocks rest unconformably upon the granite. Evidence suggests that the Carson Range was once part of the Sierra Nevada and that about 3 m.y. ago, these normal faults developed, forming the Lake Tahoe basin and leaving the Carson Range as an isolated, narrow range higher in elevation than the Sierra to the west.

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-The Sierra Nevada (highest peak Mt. Tallac, elevation 9,624 feet) lies to the west

-the Carson Range (highest elevation Freel Peak, elevation 10,881 feet) is to the east and south

-granitic rocks comprise most of the higher peaks to the south and southwest, and Miocene and Pliocene volcanic rocks cap the granitic rocks along the northwest part of the lake

-this graben developed during the past 3 million years within what was then the Sierra Nevada

-several Sierran west-flowing rivers, including branches/tributaries of the American and Rubicon rivers, were beheaded by normal faults

-Echo Summit and Donner Pass, and other Sierran passes west of Lake Tahoe are sites where these rivers were beheaded

-the Carson Range in Nevada is a remnant of a former higher crestal area of the Sierra with several of the highest peaks in the region, Rose, Freel, Jobs Sister, and Jobs peaks

-several mountain passes in the Carson Range

including Armstrong Pass, Star Pass, Daggett Pass, Spooner Summit, and Tahoe Meadows (near Mt. Rose) are remnants of the beheaded west-flowing Sierran rivers

-volcanic rocks erupted near Tahoe City area between about 2.4 and 0.9 million years (ago) dammed the basin

Lake Tahoe (the modern lake) is 22 miles long by 12 miles wide at its widest point

-the largest alpine lake in North America

-surface elevation ranges from 6,223-6,229 feet, set by a dam at the outlet at Tahoe City

-greatest depth is 1,539 feet (4,690 feet elevation)

-about the same elevation as Carson Valley, 4,700 feet above sea level

-most of the floor of the lake lies at or below 1,500 feet deep

-second deepest lake in North America (second to Crater Lake, Oregon)

-famous for lake clarity: visibility up to 60-70 feet, as noted above

-two major submerged active normal fault zones,

-West Tahoe-Dollar Point fault zone near the west shore, and

-North Tahoe-Incline Village fault zone in the north part of the lake

-a third major active fault zone, the Tahoe-Sierra frontal fault zone (TSFFZ),

-lies west of the lake within the eastern slopes of the Sierra Nevada Range

-is responsible for beheading of the American and Rubicon Rivers in the Sierra

-major displacement on the TSFFZ and related faults is younger than about 3 million years

Tahoe tsunami story (discussed below)

-unique among world’s lakes in revealing striking effects of tsunami

-between about 22,000 and 12,000 years ago, a 3.5 by 3 mile part of the

western shoreline of Lake Tahoe collapsed catastrophically into the lake

-the collapse generated very large tsunami waves that swept across all low areas around the lake including low areas in the South Lake Tahoe region

-in many areas submerged canyons and channels are carved into the sidewalls of the lake

-these are viewed as drainback channels

carved when immense volumes of water thrown up on land by tsunami

poured back into the lake.

The Ancient Ones were wise stewards of this grand place

-for thousands of years before the whites came (as outlined below).

Tahoe was ravaged during the 19th and 20th centuries

-by lumbering, water diversions, and development (discussed later under historical development).

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Basic geography and roads

Lake Tahoe, between the Sierra Nevada on the west and the Carson Range on the east, lies about 20 miles west of gold-silver mines of historic Virginia City and the famous Comstock Lode (Photo 1-5).

Highway access to the basin is provided by U.S. 50, California S.R. 89, and Nevada S.R. 431 and S.R. 207. Nevada S.R. 28 provides access to northern parts of the lake and to Crystal Bay.

U.S. 50, a major route between Sacramento and Carson City, the two state capitals, descends from the Sierra crest at Echo Summit and traverses the south part of the basin; it then skirts the west edge of the Carson Range before climbing over Spooner Summit, and then descends toward Carson City.

California S.R. 89 connects Truckee (on Interstate 80) with South Lake Tahoe (on U.S. 50), following the Truckee River to Tahoe City and then continues south along the west shore of the lake, providing access to Meeks Bay and sublime Emerald Bay.

California S.R. 28 traverses the north shore of the Lake between Tahoe City and Kings Beach, and then continues as Nevada S.R. 28 from Crystal Bay, around the east shore of the lake, climbing into the Carson Range to Spooner Summit (on U.S. 50).

Nevada S.R. 431 begins at I-580 and U.S. 395 in south Reno and climbs over 8,911-ft-Mt. Rose Summit in the Carson Range before descending to Incline Village.

Nevada S.R. 207 climbs over Daggett Pass in the Carson Range from Carson Valley and descends to the lake at Stateline, NV.

Nevada S.R. 341 provides primary access to Virginia City between Carson City and Reno.

Map 1-1. Generalized geology of the Lake Tahoe region--modified from Schweickert and Barber (2020).

WHAT THIS MAP SHOWS:

THE OBVIOUS: the crest of the Sierra is the boundary between the Sierra Nevada range and the Basin and Range Province, with the Lake Tahoe basin and Carson Range bounded by large, east-dipping, down-to-the-east normal faults. Lake Tahoe lies within a large graben between the Sierra Nevada in California and the Carson Range in Nevada. In the northwest parts of the Lake Tahoe basin, Mesozoic basement rocks in pink and shades of green are largely buried beneath Cenozoic volcanic rocks (pale orange and dark gray) and glacial deposits and basin fill (pale yellow).

THE NOT-SO-OBVIOUS: the entire area is underlain by Jurassic-Cretaceous granite (light pink) of the immense Sierra Nevada batholith. Among the granites are remnants of much older Triassic-Jurassic volcanic arc rocks (light olive green). Scattered remnants of Oligocene-Miocene rhyolitic ash-flow tuffs (light gray) were erupted from large calderas to the east. Thick, white, dashed lines mark Eocene-Oligocene paleovalleys in which rivers once flowed westward from central Nevada across the entire region; these paleovalleys were filled by the Oligocene-Miocene ash-flow tuffs. Basalt and rhyolite eruptions between about 2.5 and 0.94 m.y. ago covered large areas with flows and domes (dark gray) between Truckee, Tahoe City, and Kings Beach. The Carson Range formerly was part of the Sierra block; the Lake Tahoe basin formed less than 3 million years ago when normal faults separated the Carson Range from the Sierra Nevada. Lake Tahoe contains 2-4,000 feet of sediment eroded from the Sierra Nevada and Carson ranges. At various times during the Pleistocene, large glaciers fed by an elongate ice cap along the Sierra crest flowed eastward down glacial valleys including Ward, Blackwood, and other valleys south to Emerald Bay and Fallen Leaf Lake and into Lake Tahoe. Gray shading shows an unusual belt of Plio-Pleistocene volcanism extending east from the north Tahoe region to the Virginia Range and to Fallon, Nevada. Between about 22,000 and 12,000 years ago, a large part of the western shore of Lake Tahoe (between the Tahoe City shelf and Tahoma--the present site of McKinney Bay) collapsed into deep water producing an immense debris avalanche and very large tsunamis that swept nearly all low-lying areas around the lake. The modern Truckee River flows north from the Sierra Nevada into Pyramid Lake in Nevada.

Thick, black dashed lines show selected normal faults, such as the Tahoe-Sierra frontal fault zone (TSFFZ), West Tahoe fault (WTF), and North Tahoe-Incline Village fault zone (NTIVFZ). Various routes covered by this book are highlighted.

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How does Lake Tahoe compare with other magnificent lakes?

Lake Tahoe typically is named among the most beautiful lakes of the world. How does Tahoe compare with other famous and beautiful lakes such as Lago di Como and Lago di Garda in the Italian Alps? Lake Tahoe is larger, deeper, and higher in elevation than the famed Italian lakes (Photo 1-7). Lake Tahoe has better sandy beaches and far greater clarity. However, the magnificent Italian lakes excel in aesthetics, architecture, beautiful cities and villages, and their 2,000+-year-history stretching from Roman times!

Photo 1-7. Google Earth images at same scale of lakes Tahoe, Como, and Garda, with some vital statistics. Lago di Maggiore, another of the magnificent Italian Lakes, is intermediate in size between Como and Garda.

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Spectacular Canadian glacial lakes, including Moraine Lake and Lake Louise in Banff National Park and Maligne Lake in Jasper National Park exhibit magnificent blue colors and are enclosed within dramatic glacially carved mountains. However, these lakes, like many High Sierra glacial lakes, lack the clarity of Lake Tahoe and are relatively small (Moraine Lake 0.19 sq mi and Lake Louise 0.31 sq mi (both much smaller than Emerald Bay ~0.8 sq mi; Maligne Lake 7.6 sq mi).

A wild place

Lake Tahoe is a place of great contrasts--both overdeveloped and crowded settings and unspoiled wilderness-like areas. Federal wilderness areas include Desolation Wilderness, southwest of the lake, Granite Chief Wilderness, west of the the lake, and Mt. Rose Wilderness, north of the lake. Almost the entire Carson Range (except for highway crossings), east of the lake, and the Meiss Lake area, south of the lake, are wild areas.

The grandeur of the lake and its surrounding mountains and forests seems to belie the 19th century destruction of the old-growth forests in service of the Comstock Lode, but vestiges of that history can still be viewed in many places. Tourism and development have also threatened the basin during the past 60 years, but various local, state and federal agencies have been managing these threats for almost as long.

Tahoe bears

Photo 1-8. Photos of Tahoe bears. Top 2 scenes, BBC News-YouTube, 8/5/2016; bottom left, Keep Tahoe Bears Wild, tahoebears.com; bottom right, The Santa Rosa Press Democrat, 7/7/2021.

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Wildlife is widespread in the Lake Tahoe basin, but none is more revered than bears. As with many national and state parks, bears are prominent residents of the Lake Tahoe basin. Tahoe bears are beloved by humans here, and major efforts are underway to protect them and to live successfully together with them. Sadly, nuisance bears that are habituated to stealing human food or trash and to break-ins are often killed. Some useful notes for peaceful coexistence are below. For more information, see bearwise.org, gotahoenorth.com, tahoebears.org, and appendix.

"Six Outdoor BearWise Basics

"1. Stay Alert & Stay Together…

"2. Leave No Trash or Food Scraps…

"3. Keep Dogs Leashed…

"4. Camp Safely…

"5. Know What To Do If You See a Black Bear…

6. Carry Bear Spray & Know How To Use It …

•      DO NOT FEED THE BEARS!

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HISTORICAL DEVELOPMENT OF THE LAKE TAHOE BASIN

Lake Tahoe lies at the junction between the Sierra Nevada and the Basin and Range Province, a part of the Walker Lane belt, in the Mesozoic granitic batholith (described below and in Schweickert and Barber, 2020, Chapter 2). The basin formed within the former crestal region of the Sierra Nevada by slip on systems of normal faults, was dammed repeatedly by volcanic eruptions near its outlet, its steep mountainsides were carved by Pleistocene glaciers, and its lake-level has been modified by glacial ice dams.

As noted above, Tahoe is one of the few lakes anywhere known to have experienced a history of faulting, earthquakes, landslides, and tsunamis. Chapters below point out various lines of evidence for these events. To outline the geologic history of the basin, some of which is still controversial, we first review the geological time scale (Fig. 1-1) which will enable us to place key events in their proper historical context.

Figure 1-1. Geologic time is divided into Eons, Eras, Periods, and Epochs, with Eons (not shown here) much longer than Eras. The yellow highlights mark parts of the timescale that are important to Lake Tahoe. Numbers in parentheses following each name are the approximate time span, in m.y. (millions of years), of each Period or Epoch. Thus, Triassic strata, for example, may range in age from 251 m.y. to 202 m.y. The box shows the relative lengths, in m.y., of the Periods and of the Epochs during the Cenozoic Era. Neoproterozoic and earlier times are commonly called Precambrian. From Schweickert and Barber (2020).

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Mesozoic Era (251-65 M.Y.), Middle Life

Early to mid-Mesozoic times--Triassic-Jurassic--240-145 m.y. (millions of years) ago. The oldest vestiges of geologic history in the Lake Tahoe area are provided by small remnants of metamorphosed volcanic (metavolcanic) rocks that predate the voluminous Sierran granites. These rocks represent a marine magmatic arc active in Triassic to Jurassic times. These are exposed (Map 1-1) in areas including Mt. Tallac and Fallen Leaf Lake (Chapter 5), Blackwood and Ward Canyons (Chapter 3), and Genoa Peak and Spooner Summit (Chapter 2). Such rocks probably were deposited on much older Paleozoic rocks of the Shoo Fly Complex and related rocks (Map 1-2), which are exposed west of the Lake Tahoe basin.

Middle to Late Mesozoic Times--Jurassic-Late Cretaceous (202-75 m.y. ago). During the Jurassic and Cretaceous, immense intrusions of granitic magma within the western North American magmatic arc formed the granitic rocks of the Sierra Nevada batholith in eastern California and western Nevada (Map 1-2, Figs. 1-2, 1-3). Some of the younger granites were intruded along the trace of a strike-slip fault called the Mojave-Snow Lake fault (see below). Subaerial volcanoes in many places were fed by the granitic magmas. Some Cretaceous metavolcanic rocks have also been identified in the Carson Range. Between about 120 and 100 m.y. ago, gold mineralization occurred along the Mother Lode belt in the western Sierra Nevada.

In western Nevada between Reno and Fallon, a north-trending strike-slip fault similar in scale to the modern San Andreas fault may have developed in the Early Cretaceous. Then, a sliver of continental crust in what is now the Sierra Nevada of California (Map 1-2) moved northward along the continental margin. The sliver, called the Snow Lake block, together with other parts of the continent lying farther west, moved as much as 250 miles northward along the right-lateral strike-slip fault (as above, called the Mojave-Snow Lake fault). This large fault possibly extends northward through the Lake Tahoe region or western Nevada. If such a fault passed through western Nevada, then some of the Mesozoic and Paleozoic rocks in western Nevada and the Lake Tahoe region are way out-of-place (something for geologists to debate over beer!). Evidence that Triassic and older rocks around Lake Tahoe are far-traveled comes from Genoa Peak east of the lake (Chapter 2) and Blackwood Canyon west of the lake (Chapter 3; Map 1-2).

Map 1-2. Geologic sketch map of the Sierra Nevada, showing Lake Tahoe in relation to the Sierra Nevada batholith (pink), and pre-batholithic units, including metavolcanic rocks in nearby pendants. Possible location of the Mojave-Snow Lake fault, a right-lateral strike-slip fault, is shown by red dashed and dotted lines. Did it extend northwestward through the Lake Tahoe basin or did it veer north or northeast into western Nevada? Abbreviations: BC--Blackwood Canyon pendant, GP--Genoa Peak pendant. Modified from Schweickert and Lahren, 1993, and unpublished.

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The great granitic batholith formed as a result of rapid subduction of oceanic crust of the Farallon and Kula plates beneath western North America (Fig. 1-2). The subduction zone was in the present-day Coast Ranges of California.

Figure 1-2. Cross-section showing development of the Sierra Nevada batholith and granites of western Nevada by subduction of oceanic crust and lithosphere in what is now coastal California. From Schweickert and Barber (2020).

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Latest Mesozoic-Earliest Cenozoic Times--Late Cretaceous-Paleocene (about 75-45 m.y. ago). By latest Cretaceous time, the intrusion of granites appears to have ended. Deep erosion may have begun during this interval. An unconformity (discussed below) exposing granites beneath Cenozoic rocks is evidence for these events in the Lake Tahoe region.

Cenozoic Era (65 M.Y. To Present), Recent Life

The Cenozoic Era is divided into the Paleogene (65-23 m.y.), Neogene (23-2.6 m.y.), and Quaternary (2.6-0 m.y.) Periods (Fig. 2-1). Each of these periods is subdivided further into Epochs (e.g., Paleocene, Eocene, Oligocene, Miocene, Pliocene, Pleistocene, Holocene Epochs), giving much finer time resolution for Cenozoic events than for previous time periods.

Early Paleogene Times--Paleocene to Oligocene Epochs (65-34 m.y.). During this time, deep erosion in the Sierran region stripped miles of rock away exposing the Sierran granites in California and Nevada. The sediments derived from the erosion of the granites were deposited to the west in a forearc basin in the present areas of the Sacramento and San Joaquin Valleys of California. During the Eocene (about 50-45 m.y. ago), west-flowing rivers carved river valleys and channels across the present area of the Lake Tahoe basin and much of western Nevada and eastern California. In the 1850’s to 1870’s, prospectors discovered rich, gold-bearing gravels at the bottoms of these channels--the fabled auriferous gravels. Some of these gravels were prospected in the Carson Range near Marlette Peak and west of the lake in the Rubicon River drainage. The source(s) of the placer gold in these Eocene gravels, which have never been found, must lie east of Virginia City in Nevada.

About 40-35 m.y. ago, the crust in Nevada began to stretch east-west, and large volcanic calderas erupted to produce vast outpourings of lava and ash-flow tuff. Ignimbrites or welded ash-flow tuffs formed when massive amounts of gas-rich, high-silica magma were suddenly released from high confining pressure as volcanic calderas collapsed. Great clouds of rapidly expanding volcanic ash resulted. Fallout from the eruption clouds produced thick, flowing sheets of glowing ash and pumice that eventually cooled to form ignimbrites. This volcanic activity has been attributed to steepening and sinking of a former flat oceanic slab that may have lain beneath Nevada.

Late Paleogene to Early Neogene Times--Oligocene to Late Miocene (34-10 m.y.). Ignimbrites ranging in age from about 35 to 23 m.y. cover thousands of square miles of central and western Nevada (Fig. 1-3). Tuffs were carried along and deposited in paleovalleys like that between Marlette Peak and Blackwood Canyon (Map 1-1).

Figure 1-3. Map of central and southeastern Nevada volcanic fields and caldera belt. Calderas ranging in age from about 35 to 23 m.y. are shown by white dots. From Schweickert and Barber (2020).

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About 25 m.y. ago (near the end of the Oligocene Epoch), right-lateral strike-slip faulting began in the Walker Lane belt of western Nevada and eastern California, in which the lake Tahoe basin lies. This coincided in time with development of the San Andreas fault as a transform (strike-slip) plate boundary along the Pacific Coast. Stretching of the crust continued throughout Nevada.

Andesites were erupted from volcanic centers in the region of the present-day Virginia Range during the middle Miocene (about 18-14 m.y. ago).

About 13.7-14.2 m.y. ago (Middle Miocene), mineralization of the Comstock Lode in Nevada produced rich deposits of gold and silver; this mineralization would have profound impacts on western Nevada and the Lake Tahoe region in the 19th century.

Late Neogene--Late Miocene to Early Pliocene (10-3.6 m.y.). In the western and northwestern parts of the Lake Tahoe basin, thick sequences of andesitic mudflow breccias, lavas, and tuffs, ranging in age from about 10 to 3 m.y., are exposed. Volcanic rocks of Late Miocene age are also present at Stateline Point and Mt. Rose in the Carson Range. These andesitic rocks completely buried the older topography and form the northwest and northern margins of Lake Tahoe. Additionally, a number of volcanic plugs of Late Miocene age intrude granitic and metamorphic rocks in the present-day Carson Range. These include prominent features such as Cave Rock, Shakespeare Rock, and Captain Pomin Rock.

About 10 m.y. ago, major normal faulting occurred in the western parts of Nevada and eastern California. This phase of high-angle normal faulting began to produce the modern basin-and-range topography of Nevada, which is dominated by northeast-trending mountain ranges and parallel intervening valleys, essentially gigantic stretch marks in the crust. Large-magnitude stretching of the crust (extension) continued across much of the Basin-and-Range Province from Lake Tahoe eastward (Figure 1-5). However, the present Lake Tahoe basin probably formed by normal faulting (and possibly minor strike-slip faulting) after about 3 m.y. The normal faults truncated or beheaded various tributaries of west-flowing rivers like the Rubicon (Map 1-3).

Figure 1-4. Map of present Basin and Range topography of Nevada and the Walker Lane belt. Modified from Schweickert and Barber (2020).

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Map 1-3. Shaded relief map of the Lake Tahoe region showing simplified normal faults (red lines) and possible reconstructions of ancestral west-flowing drainages that formed by about 3 m.y. ago and predate the formation of the Lake Tahoe basin by slip on the major fault zones (data from Schweickert, 2009). Various former tributaries of the ancestral Rubicon River (blue dashed lines) were beheaded by east-side-down slip on faults of the Tahoe-Sierra frontal fault zone (TSFFZ) and by other faults to the northeast. The ancestral South Fork American River (green dashed lines) was also beheaded near Echo Summit by slip on the TSFFZ. In this map area, nearly all passes in the Sierra Nevada and Carson Range are sites where former west-flowing drainages were truncated by slip on normal faults.

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Most of the present relief of the Sierra Nevada in California has developed during the past 3-5 million years. The San Andreas fault and the Walker Lane belt continued to be active.

Pleistocene Epoch (2.6-0.01 m.y.). A shallow, ancestral lake called proto-Tahoe had developed between about 3 and 2 m.y. ago. Thick sections of silt and sand were deposited within the lake.

An unusual, ENE-trending belt of Pleistocene volcanic activity developed between the north Tahoe region and Fallon, Nevada (Map 1-1). Basaltic eruptions between about 2.5 and 0.9 m.y. produced various lava dams near Tahoe City, which raised lake level several times. Much of the modern configuration of the basin developed after about 2 m.y. ago.

During the Pleistocene Epoch there were at least 14 major glacial advances. Mountain glaciers carved deep canyons in the steep escarpment of the eastern Sierra Nevada and high parts of the Carson Range (Map 1-4).

Along the west side of the lake, the lower parts of most glacial valleys--Madden, McKinney, General, Meeks, Lonely Gulch, Eagle Creek, Cascade Creek, Tallac Creek, and Glen Alpine/Taylor Creek--are bounded by high ridges of glacial till, known as glacial moraines. These prominent glacial moraines, typical of nearly all eastern Sierran glacial valleys, are composed of boulders and sand left behind by the glaciers as they melted and retreated.

Map 1-4. Map of the Lake Tahoe basin (modifed from Plume et al., 2009; data from Schweickert et al., 2000, 2005, 2019; and Moore et al., 2014), illustrating glacial valleys (marked by red lines) and several important geologic features in and around the lake. North is to the left. Colors represent geologic units:

lake bottom--pale blue,

granite--pale lavendar,

Cenozoic volcanic rocks--orange,

glacial deposits--gray & green;

alluvial deposits--blue.

Limits of the map on west and east are defined by the crests of the SIerra Nevada and the Carson Range, respectively. Three principal active fault zones are shown by black lines and a gold band, together with labels for creeks that drain into the lake. Major glacial valleys, most in the eastern Sierra Nevada, are defined by thick red lines. Note how all Sierran glacial valleys developed along the high escarpment formed along the Tahoe-Sierra frontal fault zone; additional important glacial valleys such as Bear Creek and Olympic Valley (not shown) lie northwest of the basin, where they drained into and sometimes dammed the Truckee River. Most of the glaciers in these large valleys were fed from an ice cap that developed along the Sierra crest. Smaller ice caps may have existed along the north and south ends of the Carson Range, where smaller glaciers had developed. The postglacial McKinney Bay landslide, outlined by dashed white lines, formed by catastrophic collapse of part of the western shoreline areas (outlined by the thin white line) and removed glacial moraines from the mouths of Blackwood and Ward canyons. This event, which occurred at some time between about 22,000 and 12,000 years ago, produced major tsunamis that inundated and eroded all lowlying nearshore areas. Glacial moraines in several places along the western and southern edges of the lake are unusual (gold circles; also see Photo 1-9). In these places, as described in Chapters 2, 3, and 5, moraines are missing or were eroded and/or damaged by the tsunami. Immense volumes of water cast ashore by the tsunamis drained back into the lake and carved numerous underwater canyons and channels many of which are visible along the sidewalls of the present lake. (see Map 1-5, below).

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In contrast, in several glacial valleys, the moraines are completely missing--Ward and Blackwood--or are very subdued--Upper Truckee River (Map 1-4, Photos 1-9). These unusual cases provide important evidence of the Tahoe tsunami story, which is outlined below.

Photo 1-9. Lidar and Google Earth images of Sierran glacial valleys in the Lake Tahoe basin with pale orange shading showing the extent of large glacial moraines in the lower parts of these valleys. Well-developed moraines are preserved in the valleys of Fallen Leaf Lake (upper right), Cascade Lake-Emerald Bay (lower left), and Meeks-General-McKinney creeks (lower right). Asterisks (*) indicate that some damage has occurred, as discussed in various chapters. The Upper Truckee River canyon (upper left) oddly has extensive pre-Tahoe-age moraines but very poor preservation. Most unusual are Blackwood and Ward Creeks (center), very large and deep glacial valleys that lack glacial moraines! We shall see why below.

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During parts of the Pleistocene, glaciers repeatedly dammed the Truckee River canyon between Lake Tahoe and Truckee, California, raising the level of Lake Tahoe from about 90 to 600 feet above present levels. At various times, the glacial dams burst, causing catastrophic floods (known as jokulhlaups) downstream. Bouldery outwash deposits in stream terraces formed by jokulhlaups can be seen