Dutch Flat District

Site Name

Primary: Dutch Flat District
Secondary: Southern Cross
Secondary: Polar Star
Secondary: Alta
Secondary: Nichols Diggings
Secondary: Blue Devil Diggings
Secondary: Nary Red
Secondary: Banner
Secondary: Bear River Hill
Secondary: Queen City
Secondary: Cedar Creek
Secondary: Dutch Flat Drift
Secondary: Indian Hill Drift
Secondary: Consolidated Junction
Secondary: Comet
Secondary: Canyon
Secondary: Dyer Drift
Secondary: Federal Drift
Secondary: Flying Fish
Secondary: Golden Shaft
Secondary: Gould Group
Secondary: Hoose
Secondary: Haub Drift
Secondary: Stewart Drift
Secondary: Moody Ridge Drift
Secondary: Garden Claim
Secondary: North Fork
Secondary: Bear River
Secondary: Bear River Tunnel
Secondary: Little Bear
Secondary: Big Blue Quartz
Secondary: North Star Quartz
Secondary: Morgan Asbestos Mine

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Commodity

Primary: Gold
Secondary: Platinum
Secondary: Silver
Tertiary: Lead
Tertiary: Iron
Tertiary: Zinc
Tertiary: Copper
Tertiary: Indium

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Location

State: California
County: Placer
District: Dutch Flat District

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Land Status

Land ownership: National Forest
Note: the land ownership field only identifies whether the area the mine is in is generally on public lands like Forest Service or BLM land, or if it is in an area that is generally private property. It does not definitively identify property status, nor does it indicate claim status or whether an area is open to prospecting. Always respect private property.
Administrative Organization: Tahoe National Forest

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Holdings

Not available

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Workings

Not available

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Ownership

Owner Name: Various private owners

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Production

Not available

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Deposit

Record Type: District
Operation Category: Past Producer
Deposit Type: Stream placer; hydrothermal vein
Operation Type: Surface-Underground
Discovery Year: 1849
Years of Production:
Organization:
Significant: Y
Deposit Size: S

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Physiography

Not available

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Mineral Deposit Model

Model Name: Low-sulfide Au-quartz vein
Model Name: Placer Au-PGE

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Orebody

Form: Irregular; Tabular, lens

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Structure

Type: R
Description: Melones Fault Zone, Gillis Hill Fault Zone

Type: L
Description: Melones Fault Zone

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Alterations

Alteration Type: L
Alteration Text: NA?Negligible - none described

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Rocks

Name: Argillite
Role: Host
Age Type: Host Rock
Age Young: Triassic
Age Old: Permian

Name: Slate
Role: Host
Age Type: Host Rock
Age Young: Triassic
Age Old: Permian

Name: Sand and Gravel
Role: Host
Age Type: Host Rock
Age Young: Tertiary

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Analytical Data

Not available

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Materials

Ore: Gold
Gangue: Quartz

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Comments

Comment (Geology): Regionally, the northern Sierra Nevada experienced a long period of Cretaceous to early Tertiary erosion, after which it underwent extensive late Oligocene to Pliocene volcanism. The oldest Tertiary deposits are basal Eocene auriferous gravels, which are preserved in paleochannels eroded into basement and on adjacent benches; both were deposited by the predecessors of the modern Yuba and American Rivers. In contrast to earlier volcanism, Tertiary volcanism was continental, with deposits placed on top of the eroded basement rocks, channel deposits, and Mesozoic intrusives. Two regionally important units are the Valley Springs and Mehrten Formations. The Oligocene-Miocene Valley Springs Formation is a widespread unit of intercalated rhyolite tuffs and intervolcanic channel gravels that blanketed and preserved the basal gravels in the valley bottoms. The younger Miocene-Pliocene Mehrten Formation consists largely of andesitic mudflows, which regionally blanketed all but the highest peaks and marked the end of Tertiary volcanism. Pliocene-Pleistocene uplift of the Sierra Nevada caused the modern drainages to erode through the volcanic Valley Springs-Mehrten sequences and carve deep river gorges into the underlying basement rocks. During this process, the modern rivers became charged with placer-gold deposits from both newly eroded basement rocks and from the reconcentration of the eroded Tertiary placers. The discovery of these modern Quaternary placers in the American River is what sparked the California Gold Rush. Tertiary Channel Gravels It has been estimated that 40 percent of California's gold production has come from placer deposits along the western Sierra Nevada (Clark, 1966). These placer deposits are divisible into Tertiary deposits preserved on the interstream ridges, and Quaternary deposits associated with present streams. Tertiary gravels can be further divided into basal Eocene, or "auriferous" gravels, which rest on basement, and younger "intervolcanic" gravels within the overlying continental volcanic units. During the Cretaceous, the Sierra Nevada was eroded and its sediments transported westward by river systems to a Cretaceous marine basin. By the Eocene, the Sierra Nevada was more hilly than mountainous and of lower relief than present. Low gradients and a high sediment load allowed the valleys to accumulate thick gravel deposits as the drainages meandered over flood plains up to several miles wide developed on the bedrock surface. The major rivers were similar in location, direction of flow, and drainage area to the modern Yuba, American, Mokelumne, Calaveras, Stanislaus, and Tuolumne Rivers. Their auriferous gravels deposits are scattered throughout a belt 40 - 50 miles wide and 150 miles long from Plumas County to Tuolumne County. In the northern counties, continuous lengths of the channels can be traced for as much as 10 miles with interpolated lengths of over 30 miles. The ancient Yuba River was the largest and trended southwest from headwaters in Plumas County. Its gravels are responsible for the large placer deposits at San Juan Ridge and North Columbia in Nevada County. Tributaries of the Yuba are responsible for the deposits at Dutch Flat.

Comment (Geology): GEOLOGY OF THE DUTCH FLAT DISTRICT Throughout most of the Dutch Flat District, only the basement rocks of the Calaveras Complex and the overlying Eocene auriferous gravels are present. While thick sections of Oligocene to Pliocene Valley Springs and Mehrten Formation rocks are present to the south in the districts of the Forest Hill Divide, and northwest in the Scott's Flat District, they have been largely lost to erosion in the Dutch Flat District. Limited outcroppings of the Valley Springs and Mehrten Formations are present on the east edge of the district near Alta and Towle and along Moody Ridge to the south. The main body of basement rocks within the district consists of a belt of north-northwest trending steeply dipping, slate, argillite, amphibolite, phyllite, chert, and metavolcanic rocks of the Calaveras Complex. Gabbroic and serpentinite intrusions are common to the east. Immediately west of the district, the Foresthill Fault, a steep easterly dipping thrust fault, cuts the Calaveras Complex. To the east of the district, the Goodyears Creek Fault of the Melones Fault Zone (Clark, 1960) separates the Calaveras Complex from partially to completely serpentinized peridotite of the Feather River Peridotite Belt. Basal Eocene Auriferous Gravels Due to localized erosion of the Valley Springs and Mehrten Formations, the Dutch Flat and neighboring districts were known for their immense bodies of exposed auriferous gravel. The total area of exposed gravels in the district approached 1-2 square miles. The district is located at the junction of three tributary channels of the Eocene Yuba River. The main tributary flowed northward from the adjacent Gold Run District before turning sharply southwest in the Dutch Flat area. From there, it crossed the present Bear River about a mile west of Dutch Flat, and then flowed 2-3 miles through the You Bet District where it was mined at the Christmas Hill and Little York Diggings. It then turned sharply north and flowed through the Red Dog and Hunt's Hill areas to its confluence with the Yuba River near North Columbia. A second channel flowed southwest from the Lowell Hill District and merged with the main tributary at Dutch Flat. A third, smaller channel entered the district from the Shady Run area to the east and also joined the main tributary at Dutch Flat The Eocene gravels at Dutch Flat achieve a maximum thickness of 300 feet and can be divided into lithologically and texturally distinct units. The lower unit, or ?blue lead? of the early miners, averages 150 feet thick, rests directly on bedrock, and contains most of the gold. It is generally confined to the wide channel troughs on bedrock and buried under thick sections of upper gravel. The main tributary channel at Dutch Flat forms a distinct trough about 300 feet deep in which bedrock is in part polished and hummocky and in part soft and decomposed. Channel grade is as much as 10 feet in 100 feet. Based on an analysis of 26 samples collected throughout northern Sierra Nevada, the lower gravel unit averaged: cobbles and boulders, 13% (with boulders of up to several feet); pebbles, 56%; granules and sand, 28%; silt and clay, 3% (Yeend, 1974). Cobbles can average over 8 inches in diameter, and boulders may reach 8-10 feet in diameter. There is relatively little sand. The lower gravels are generally immature and composed of bluish-black slate and phyllite of the Calaveras Complex, weathered igneous rocks, and quartz. Chlorite, amphibole, and epidote mineral grains are also common components. Lower gravels are well-cemented, more suited to drift mining, and generally required crushing in stamp mills. While no specific information is available for Dutch Flat, the lower gravels were reported to have yielded as much as $9/cubic yard in the neighboring Gold Run District. Almost all of the blue lead gravels in the district have been drifted.

Comment (Environment): The Dutch Flat District encompasses an area on the northwest flank of Moody Ridge in northern Placer County approximately midway between Sacramento and Lake Tahoe (55 miles northeast of Sacramento). Moody Ridge is a northeast-trending ridge, which locally separates the North Fork of the American River from the Bear River to the north. The ridge is bisected by Canyon Creek, which flows to the southwest and parallels Interstate 80 for part of its course. Drainage to the west is into the Bear River and to the east into Canyon Creek and the North Fork of the American River. The area is generally rural, with the small community of Dutch Flat located near the center of the district and the smaller communities of Alta and Towle located along its eastern edge. The nearest large city is Auburn (pop.13,300), located 25 miles to the southwest. Topography is dominated by heavily forested, mountainous terrain dissected by riverine canyons, which support a cover of mixed oak, conifer, and chaparral. The town of Dutch Flat lies at an elevation of 3,144 feet, and relief between the town and the Bear River to the north is 650 feet. Relief from the crest of Moody Ridge (south of town) to the North Fork of the American River to the south is 2,400 feet. Moody Ridge is dissected by many small gullies and ravines, which support mostly ephemeral streams. The former hydraulic pits and drift-mine adits are largely located on the northern flank immediately west and northwest of Dutch Flat and above the Bear River where auriferous gravels were naturally exposed by uplift and erosion. The denuded, abandoned hydraulic workings at Nichols Diggings and Blue Devil Diggings make up most of the terrain north and west of town. The climate is intermediate between the moderate conditions of the rolling lower Sierra Nevada foothills and the alpine conditions near the crest of the Sierra. Average monthly temperatures range from a low of about 35?F in January to a high of about 90? in July. Mean annual precipitation is approximately 48 inches, most of which falls during the rainy winter months between November and May.

Comment (Location): The Dutch Flat District includes numerous small, individual mines distributed throughout an area encompassing approximately 8-10 square miles on the northwest flank of Moody Ridge (once known as Dutch Flat Ridge), north of the Union Pacific Railroad and Interstate 80 and south of the Bear River. Since the majority of workings were located around the community of Dutch Flat, the community itself was chosen to represent location of the district. The location latitude and longitude identify the USGS 3,144-foot elevation benchmark located near the center of the community on the USGS Dutch Flat 7.5-minute quadrangle (approximately center of Sec. 34, T15N, R10E, MDBM). Dutch Flat is reached by taking Interstate 80 east for approximately 25 miles past Auburn to the Dutch Flat exit. The town is one mile north of the exit, on Sacramento Street.

Comment (Development): Placer mining in the Dutch Flat District began with the discovery of modern placer deposits in the gravels of the Bear River in 1849. Dutch Flat was established in 1851 when two German brothers, Joseph and Charles Dornbach, made camp on the bluff overlooking the Bear River. Local miners originally called the camp "Dutch Charlie's Flat," but when the town was granted a post office in 1856 it was formally named ?Dutch Flat.? Besides its prominence as a mining center, it became a stage and railroad station, making it one of the largest, and most important towns in the county from 1864 to 1866. In 1859, a possible rail route was proposed through Dutch Flat and across the Sierra. The railroads realized the value of the proposed route and the Central Pacific Railroad became a reality. The first shares in the venture were subscribed in Dutch Flat. In 1866, after the railroad had reached Cisco, 20 miles farther east, Dutch Flat lost much of its importance as a stage stop. As the modern placers in the Bear River played out, attention turned to the Eocene gravels on the bluffs north of Dutch Flat as the miners migrated from the river canyon to these new grounds. By the late 1860s, the construction of the railroad had caused Dutch Flat's Chinatown to become one of the largest Chinese settlements outside of San Francisco (Logan, 1936). While the Bear River placers paid well during the early years and limited drift mining of the Eocene blue lead gravels was proving productive as early as 1856, it was the introduction of hydraulic mining in 1857 that caused the town and district to flourish. Hydraulic mining commenced on small individual claims such as the Phoenix, American, Buckeye, Dutch Flat, and Queen City claims. While the claims were small, the yield was high. In October 1859, the Placer County Canal was completed to Dutch Flat providing sufficient water to implement large-scale hydraulic mining. Several individual claims were productive, but there are no detailed records for any of the early mines. However, the Badger Claim reportedly produced $192,000 in dividends in four years. During the following five years, the hydraulic mines were highly productive. At Dutch Flat's peak during the 1860s, approximately forty-five hydraulic claims were being worked within a 1.5-mile radius of town. A production of about $150/day was the average for a claim using 250 inches of water and employing 4-6 men (Logan, 1936). By 1867, most of the easily washed upper gravels had been worked, and the first shaft was sunk to bedrock on the Buckeye claim to exploit the lower Eocene blue lead on bedrock. In 1867, the first milling of the hard gravel occurred on the Ohio claim. Subsequently, most blue lead gravels between Dutch Flat and the Central Pacific Railroad were worked by drifting (Logan, 1936). Almost no information is available about these early mines. Most were unpatented and in later years were relocated under other names. During the 1870s, hydraulic mining operations reached their peak. In 1872, the Cedar Creek Company of London purchased and consolidated over 30 claims. They introduced large scale hydraulic mining and reportedly produced "millions.? Dutch Flat was one of the first mining camps where newly invented dynamite was extensively used in hydraulic mining to break up and collapse the gravel faces. The hydraulic mines in the area continued to produce fantastic amounts of gold well into the 1870s. A Chinese company reportedly found a $12,000 nugget in July of 1877. The gold at Dutch Flat assayed as high as .970 fine.

Comment (Geology): Continued uplift during the Pliocene-early Pleistocene increased gradients allowing the modern drainages to cut through the volcanic mantle and auriferous gravel deposits and deeply into basement. The once-buried Tertiary river gravels were left exposed in outcrops high on the flanks of the modern drainage divides. In the Dutch Flat region, volcanic rocks of the Mehrten Formation are preserved on the tops of many of the more prominent drainage divides including the Forest Hill Divide and Moody Ridge. Lode Quartz Gold and silver also occur in fracture-filling mesothermal quartz veins, which generally occur in three northwesterly trending bedrock zones. The westernmost zone, composed of Mariposa Formation slates, follows the Gillis Hill Fault Zone to Colfax, where it continues northward within diabase, granodiorite, and amphibolite into Yuba County. The other two zones of mineralization are east of the Gillis Hill Fault within rocks of the Calaveras Complex and the Feather River Peridotite Belt. No significant deposits have been found in the Calaveras Complex bedrock of the Dutch Flat District. Structure Most Upper Jurassic and younger basement rocks of the northern Sierra Nevada were metamorphosed and deformed during the Jurassic-Cretaceous Nevadan Orogeny (Clark, 1960). The dominant northwest-trending structural grain is a result of this period of compressive deformation, which produced thrust faults, major northwest-trending folds, and regional greenschist facies metamorphism (Harwood, 1988). This episode also resulted in the intrusions of granitic plutons that formed the Sierra Nevada. Nevadan deformation structures within and between the northern Sierra Nevada lithotectonic blocks are steeply dipping northwesterly trending faults and northwesterly trending folds. These features are best developed in the Eastern, Central, and Feather River Peridotite Belts, where the faults have been collectively described as the "Foothills Fault System" (Clark, 1960). They deform Upper Jurassic rocks and are truncated by uppermost Jurassic and Cretaceous plutons. Where the attitude can be determined, most of the bounding faults dip steeply east and display reverse displacement. The regional northwest-trending structural grain is also at approximately right angles to the prevailing direction of stream flow of both the ancient and modern channels. This grain, locally expressed in the form of foliation and cleavage in the metamorphic bedrock, served as a good trapping mechanism for the eroded particles of gold as they were transported downstream from primary sources in the lode deposits. Metallogeny The northern Sierra Nevada contains many mining districts, each known for important deposits of lode and/or placer gold. Most significant exposed lode deposits have probably been discovered given the intense scrutiny the area was subjected to during the latter half of the 19th century. Still of significance are the placer deposits in the Tertiary gravels. Lengths of buried Tertiary channels remain undeveloped, underdeveloped, or undiscovered. The complex interbedded nature of some of the channels and the extensive cover of Valley Springs and Mehrten Formations undoubtedly obscure many rich placer gravels. Further, after the 1884 Sawyer Decision curtailed hydraulic mining, lower-grade gravels were ignored in preference of the richer gravels, which could be profitably mined by drift methods. Merwin (1968) concluded that the demise of hydraulic mining in California resulted in more than half of the then-known gravels remaining unexploited. He valued these reserves at $750 million - $1 billion dollars (1966 dollars at $35.00/oz.). At today's price of approximately $300/oz, this equates to $6.4 to $8.6 billion.

Comment (Development): Activity essentially ceased in the district after the 1884 Sawyer Decision injunctions, which affected debris disposal. By as early as 1876, the Dutch Flat hydraulic mines had already deposited tailings 70 feet deep in the Bear River below. Plans to remedy this situation by driving a 3-mile tunnel under Moody Ridge and sending the debris to the North Fork of the American River were considered too expensive and thus abandoned (Logan, 1936). By 1890, almost all of the mines were idle and the town was partially deserted and decaying. Since the deeper blue gravels were known to be rich, efforts were made to consolidate smaller claims on the channel and open the deeper channel for drifting. In 1895, the Polar Star and Southern Cross Mines (Sec. 34, T16N, R10E) were operated by drifting, followed by renewed hydraulic mining of the coarse blue lead gravels. In 1900, the Polar Star was using 2,800 inches of water under 450-foot head with 8 and 9 inch nozzles. This was only enough water to permit work for 5 hours a day. A log debris dam was built in the Bear River and was used jointly by this mine and the Liberty Hill Mine in Nevada County to the north. Drift mines that were active about the same time were the Dutch Flat Blue Lead Mine, which worked a cemented bottom gravel that required crushing in a 10-stamp mill, the Alta Mine, and the Bartley Consolidated Mine, which was on the branch channel coming from Alta. The latter two mines produced low-grade gravel from a drift-mining standpoint. After 1914, there was no hydraulic mining, and drift and quartz mining were drastically reduced county-wide. By 1916, the only gold mines reported to be "active" in the district were the Rawhide Quartz, Federal Drift, Dyer Drift, Dutch Flat Drift, Haub Drift, Indian Hill Drift, Moody Ridge Drift, and Stewart Drift. Of those, only the Dyer Drift and Stewart Drift were reportedly producing, the remainder undergoing only assessment work (Waring, 1917). In 1933, the Enterprise Leasing Company obtained mining rights under a number of Dutch Flat town lots to prospect unworked gravels underlying the town itself. They erected a mill, and a 125-foot shaft was sunk to basement with considerable drifting. Only 100 ounces of gold were reportedly produced during 1934, and the project was abandoned. In August 1935, Lyman Gilmore and Associates filed a mining location in town on a portion of the gravels that had been excluded from the 1876 town-site grant. There is no record of any work being done on this location. As of 1936, no significant mining was being done in the district (Logan, 1936). The total gold production of the Dutch Flat District is unknown. While the figure of $3 million has been attributed to the district as of 1867, Logan (1936) estimated the district to have ultimately produced at least $4.5 to $5 million.

Comment (Workings): Noteworthy Mines in the Dutch Flat District Very little specific information regarding the numerous individual mines in the Dutch Flat District is available. The following descriptions are thus necessarily brief and may be incomplete. Southern Cross and Polar Star Mines (Sec. 34, T16N, R10E) The Polar Star and Southern Cross mines consisted of 140 acres within the heart of the district immediately northwest of Dutch Flat. These adjacent mines were first hydraulically mined for the poorly consolidated upper unit of the Eocene gravels. After the initial hydraulic mining, a thick section of basal blue lead gravel remained. In the 1890s these remaining deposits were drift mined. As of 1896, drifting had been conducted at different points on the claims in a lower gravel bank 160 feet high. The main tunnel was 300 feet long, and the deep bedrock channel was 40 feet wide. The gravel carried 80% boulders, which were left underground. Breasts were 7 feet high and 40feet wide and timbered with post and cap (Crawford, 1896). In 1885, the Polar Star Mine was reported to have produced a single quartz boulder that yielded $5,780. In later years, hydraulic mining was applied to the remaining blue lead gravels in the Southern Cross and Polar Star mines. William Nichols conducted this deeper hydraulic mining, which exposed bedrock throughout the large area called Nichols Diggings, northwest of Dutch Flat. Where the deep gravels had previously been drifted, the yield was $0.25/cubic yard, and where not drifted the yield was $0.40/cubic yard. Alta Drift Mine (Sec. 36, T16N, R10E) As of 1896, the Alta Mine had a main working tunnel 2,900 feet long within the blue lead gravel of the smaller Eocene tributary entering the district from the east. A 180-foot water-blast ventilation shaft tapped the tunnel at 2,400 feet. Three crosscuts in gravel were developed: one driven northwest was 120 feet long, and one driven southeast was 216 feet long. A third had just been started. About 30-40 carloads of gravel were broken in breasting each day. The gravel contained about 60% boulders and cobbles, which were stored in the mine. A wash dump held 200 cars of 1-ton capacity. A 400-foot flume discharged into Canyon Creek and used about 90 miner?s inches of water for washing (Crawford, 1896).

Comment (Economic Factors): Although no exact figures are available, it has been estimated that 105,000,000 cubic yards of gravel have been washed at Dutch Flat. Jarmin (1927), in his report to the State Hydraulic Mining Commission, estimated that about 17,000,000 to 34,000,000 cubic yards of gravel remain unworked at Dutch Flat. The total production of the Dutch Flat mines can only be guessed. The district was one of the leading hydraulic producers in the county and contained many small mines, some of which were later consolidated. The figure of $3,000,000 in gold production has been credited to the district by 1867. Logan (1936) estimated total district production at between $4.5 - $5.0 million.

Comment (Identification): The Dutch Flat Mining District is located about 10 miles northeast of the town of Colfax in north-central Placer County, California, next to the Nevada County line. It encompasses the Alta and Towle areas, which at one time were considered separate districts. The district includes all gold-quartz lode and placer mines in the vicinity of the communities of Dutch Flat, Monte Vista, Alta, and Towle, and for the most part, north of the former Southern Pacific Railroad (currently Union Pacific) line. The district also includes a few small chromite and asbestos mines in the Alta and Towle areas, but these deposits are not covered in this report. The district is bordered by the You Bet District to the west, the Gold Run District to the south, and the Lowell Hill District to the northeast. The district is known as a placer-gold district, the majority of production having come from hydraulic and drift mining of auriferous Eocene gravel deposits. Gravel deposits consisted of a lower, generally well-cemented, basal unit, which contained most of the gold, and a finer and less-consolidated overlying unit. A few small lode-gold prospects and mines were reported in the district, but none were significant producers.

Comment (Workings): Drift mining involved driving adits and tunnels along or close to the lowest point in the bedrock trough of an ancient channel and following it up or down stream along the channel thalweg. While some deeply buried channels were originally accessed through vertical shafts, drainage problems and the expense of hoisting limited the use of shafts, which led to most drift mines being accessed through tramway and drain tunnels driven into bedrock below the channels. Channels were usually located by gravel exposures on hillsides and terraces. Exposures of upstream and downstream gravels were called ?inlets? and ?outlets,? respectively. Where a ravine or canyon cut into, but not through an old channel, the exposure was called a ?breakout.? The preferred method of developing an inlet was to tunnel through bedrock under the channel at such a depth and angle as to break through into the bed of the channel providing natural drainage. The overlying gravels could then be accessed directly through the tunnel or by periodic raises and drifts. Development of an outlet involved following the bedrock channel directly into the hillside, the incline of the bedrock providing natural drainage. Prospecting and developing a breakout was more difficult, since the exposed gravel could be in the basal channel or hundreds of feet up on the edge of the channel, making it impossible to locate a prospect tunnel with any certainty. The surest method of prospecting was to run an incline on the pitch of the bedrock. Another method was to sink a vertical shaft on the presumed channel axis. The former method proved superior since it involved less subjectivity and often uncovered paying bench gravels on edges of the old stream. Once the bed of the channel was located, it was prospected by drifts and cross-cuts to ascertain width, direction, grade, and the location, extent, and quality of pay. The tunnel entrances were generally in or near a ravine or gulch for easy waste- rock disposal. Prospecting also included projecting the grade and direction of existing channel segments for distances up to several miles. Thus having determined a potential location, a prospect adit or shaft was driven to evaluate it. This was a common method of finding old channels where there were no surface exposures. Access tunnels were driven in bedrock to minimize timbering and ensure a stable roof, through which raises were driven to work the placer gravels. Tunnels were generally run under the lowest point of the bed of the channel in order to assure natural drainage and to make it possible to take auriferous gravels out of the mine without having to hoist it. Working upstream in a channel with a uniform grade, the main tunnel could be run on the surface of the bedrock. The main drifts were kept as straight as possible and in the center or lowest depression of the channel. To prospect the width of the channel, crosscuts at right angles to the drift were driven on each side to the rims of the channels or the limit of the paying lead. These were timbered and lagged in soft gravels, but not to the extent of the main drift. In wide pay leads, gangways paralleled the main tunnel to help block out the ore in rectangular blocks. In looser intervolcanic gravels, timbering was required and the main difficulty was preventing caving until timbering was in place. The looser gravels were excavated with pick and shovel.

Comment (Geology): The upper gravels form the majority of the Eocene gravel deposits and, unlike the lower gravels, are well-exposed in cliffs and bluffs along the old river channels. Their thicknesses vary significantly within the district. These gravels are much finer, with clasts seldom larger than pebble size and characterized by an abundance of clay and silt beds. Large-scale cross-bedding and cut-and-fill features are common. Upper gravels are mature; quartz predominates, and the heavy-mineral content consists almost exclusively of zircon, ilmenite, and magnetite. Unlike the lower gravels, chlorite, amphibole, and epidote are absent. Gold values in the upper gravels are low, often no more than $0.02/cubic yard. However, between Dutch Flat and Indiana Hill to the south, the upper sands were reported to average $0.11/cubic yard. Lode Gold Deposits A few small lode gold prospects and mines were reported within the Calaveras Complex bedrock in the district. None were significant producers, however, and almost no information is available. Structural Disturbance With the exception of the westward regional tilting of the Sierra Nevada, there is very little evidence of any significant post-Cretaceous structural disturbance in the vicinity of the Dutch Flat District.

Comment (Deposit): The Dutch Flat District is an important Tertiary placer-gold mining district in the northern Sierra Nevada. It is most famous for its hydraulic mines within the auriferous Eocene channel gravels of a tributary of the ancient Yuba River. While a very few small gold-quartz lode prospects were pursued in the basement rocks of the district, none proved to be significant producers. The predominant ores were Eocene channel lag and bench gravels deposited on the eroded bedrock surface and later elevated by uplift of the Sierra Nevada and exposed subsequently through downcutting by modern drainages. The auriferous gravels were deposited at the confluence of three channels, which comprised a principle tributary to the ancient Yuba River to the north. The primary tributary flowed north from the Gold Run District before turning sharply southwest for about two miles through the Dutch Flat District. A second and third channel flowed southwest from the Lowell Hill District and westerly through the Shady Run area, respectively, before joining the main tributary at Dutch Flat. From Dutch Flat, the main channel flowed westerly and northerly through the You Bet District toward the main Yuba River at North Columbia. The district contained many small drift and hydraulic mines. Placer mining began at Dutch Flat in 1849 and drift mining in 1856. Hydraulic mining was introduced in 1857. The cumulative effect of the hydraulic mines was quite extensive and is still visible to the north and west of Dutch Flat at Nicholas Diggings and Blue Devil Diggings. Hydraulic mining prevailed until the Sawyer Decision of 1884 curtailed hydraulic mining, after which only limited drift mining and hydraulic mining occurred. The Eocene gravels can be divided into upper and lower units. The lower unit, which contains most of the gold, rests within trough-shaped depressions eroded in bedrock . The main tributary trough was 300 feet wide. These lower gravels were commonly referred to as the ?blue gravels? or ?blue leads? due to their bluish cast, which resulted from the predominance of blue-gray slate and phyllite clasts eroded from the Calaveras Complex. Lower gravels were generally well-cemented and composed of cobbles and quartz boulders of up to many tons. They ranged in thickness from 100-200 feet in the main tributary and were largely exploited by drift mining. Their cemented nature necessitated blasting and crushing. Pay zones were commonly erratic, but often meandered from one side of the channel to the other reflecting relict current velocities. Gold particles tended to be flat or rounded and ranged from fine flour gold to large nuggets. The upper gravels were finer-grained, much leaner in gold content, and more mature, consisting primarily of quartz pebbles, sands, and clay. They were widely exposed in hillsides and bluffs. The upper sands were not highly cemented and were mined by hydraulic mining.

Comment (Geology): Bedrock erosion degraded the rich gold-bearing veins and auriferous schists and slates as the rivers crossed the metamorphic belts of the Sierra Nevada. Upstream of the gold belts on the granitic Sierra Nevada batholith, channels are largely barren, but become progressively richer as they cross the metamorphic belt and the Mother Lode trend. They become especially enriched after crossing the gold-bearing ?serpentine belt? (Feather River Peridotite Belt) upstream of many Tertiary placer districts, including Dutch Flat. Large volumes of placer gold accumulated in the basal gravels composed largely of resistant quartz and metamorphic bedrock fragments. Blue-black slate and schist fragments often imparted a bluish hue to the gravels, hence the term "blue leads" or "blue gravels.? These basal channels have been the most productive as a whole and grade upward into finer quartz sand, pebbles, and laminated clays. Adjacent to the bedrock channels, broad gently sloping benches received shallow but extensive accumulations of auriferous overbank gravels sometimes 1-2 miles wide. Gold particles tend to be flat or rounded and range from fine flour gold to nuggets of 100 or more ounces. Large nuggets were especially prevalent in the Alleghany, Columbia, Downieville, and Sierra City Districts. The gold particles are almost everywhere associated with black sands composed of magnetite, ilmenite, chromite, zircon, garnet, pyrite, and in some places platinum. In the northern Sierra, the gold content of the gravels varies greatly. In general, the upper sands and gravels are very lean. While the most gold is contained in the lower sand and gravel, the majority of rich material is within only a few feet of bedrock. Generally, in drift mines only these lower gravels were exploited; however, in hydraulic mines the whole gravel bed was washed. Lindgren (1911) estimated that on average, the hydraulic washing of thick gravel banks up to 300 feet, including both basal and upper gravels yielded approximately $0.10 to $0.40/cubic yard. Upper gravels alone might average $0.02 to $0.10/yard and lower gavels from $0.50 to $15/yard or more. Valley Springs Formation After deposition of the Eocene channel gravels, Oligocene-Miocene volcanic activity in the upper Sierra Nevada radically changed drainage patterns and sedimentation. The first of many eruptive rhyolite flows filled the depressions of most river courses covering the Eocene gravels and diverting the rivers. Many tributaries were dammed, but they eventually breached the barriers and carved their own channels within the rhyolite fill. Ensuing intermittent volcanism caused recurrent rhyolite flows to fill and refill the younger channels resulting in a thick sequence of intercalated intervolcanic channel gravels and volcanic flows. In the Dutch Flat District, very little of the Valley Springs Formation remains, having been lost to erosion. Mehrten Formation Volcanism continued through the Oligocene to the Pliocene, with a change from rhyolitic to andesitic composition and a successively greater number of flows. During the Miocene and Pliocene, volcanism was so extensive that thick beds of andesitic tuffs and mudflows of the Mehrten Formation blanketed the Valley Springs throughout the northern Sierra Nevada. Thicknesses ranged from a few hundred to a few thousand feet. Pleistocene erosion removed much of these deposits, but remnants cap the axes of many existing ridges at mid-elevations. In some of the Tertiary river valleys, thick sequences of up to 1,500 feet of Valley Springs and Mehrten beds remain.

Comment (Workings): HYDRAULIC MINING Hydraulic mining methods were first applied at Dutch Flat in 1857. Hydraulic mining allowed the bulk processing of large volumes of low-yield Upper Eocene gravels that would otherwise be unprofitable by other methods of mining. Hydraulic mining involved directing a powerful stream of high-pressure water through large nozzles called monitors, or "giants," at the base of a gravel bank, undercutting it and allowing it to collapse. Large gravel banks several hundred feet high were mined in this manner, but larger banks were often hydraulicked in two or more benches. In some cases, adits were driven into the exposed face and loaded with explosives to help break down the exposure. The resulting slurry of clay, sand, gravel, and gold was washed through sluice boxes to trap the gold. The sluice boxes were generally four feet wide and deep and often over a thousand feet long and lined with riffles or other devices to mechanically trap the gold. Mercury was added to amalgamate the finer gold. The remaining debris was indiscriminately dumped in the nearest available stream or river. One of hydraulic mining's highest costs was in the ditches, flumes, and reservoirs needed to supply sufficient volumes of water at high pressure. A mine usually needed its own system of ditches and flumes to deliver water from distant and higher reservoirs or rivers. A mine might have 10-20 or more miles of ditches as well as dams and reservoirs, flumes, and tunnels. Several major ditches brought water to the hydraulic mines at Dutch Flat from the Bear, North Fork of the American, and Yuba rivers. At the mine site, the water passed through large iron pipes into the monitors. Hydraulic mining flourished for about 30 years until the mid-1880s when the Sawyer Decision curtailed debris disposal. Another expensive undertaking was often finding an outlet for the debris. As the gravels were washed lower and lower in the ancient channel beds, it was often necessary to drive a tunnel through the bedrock channel rim to drain the workings into a nearby canyon. The primary hydraulic mining operations in the Dutch Flat District were on the gravel exposures to the north and west of the town of Dutch Flat on the bluffs above the Bear River. Most hydraulic mining was focused on the poorly consolidated upper gravel unit of the Eocene gravels. In most cases, the hydraulic mining was preceded or followed by drift mining of the harder cemented lower blue lead gravels. Most of the hydraulic mining activity at Dutch Flat occurred as small individual operations on individual claims of only a few tens of acres. Two of the larger and more famous mines, the Polar Star and Southern Cross mines (Sec. 34,T16N, R10E) comprised 140 acres and were intermittently mined by hydraulic and drift methods. Along with several other smaller operations, these mines worked the gravels all the way to bedrock and are responsible for the large hydraulic workings immediately northwest of Dutch Flat. These workings, which comprise over a half-square mile, are known as the "Nichols Diggings.? Several other operations are responsible for the considerable bedrock exposures in the Blue Devil Diggings just west of town. DRIFT MINING Drift mining of the lower blue lead gravels at Dutch Flat commenced in 1856 and was followed in 1857 and later years by extensive hydraulic mining. Drift mining at Dutch Flat was far less extensive than in the more famous drift mining districts of the nearby Forest Hill Divide.

Comment (Commodity): Commodity Info: Placer deposits: Placer gold dust to large nuggets. Placer gold was approximatly .970 fine. Lode deposits: Free-milling gold-bearing quartz veins.

Comment (Commodity): Ore Materials: Native gold

Comment (Commodity): Gangue Materials: Quartz and metamorphic gravels; quartz

Comment (Geology): INTRODUCTION The Dutch Flat District is primarily a placer gold district having produced from thick sections of exposed Eocene auriferous channel gravels. Only minor production was obtained from a few small lode mines. The district also includes a few rather insignificant asbestos and chromite mines, which are not discussed herein. REGIONAL SETTING The northern Sierra Nevada is home to numerous placer and lode gold deposits. It includes the famous lode districts of Johnsville, Allegheny, Sierra City, Grass Valley, and Nevada City and the famous placer districts of La Porte, North Columbia, Cherokee, Michigan Bluff, and Forest Hill, and Dutch Flat. The geological and historical diversity of most of these deposits and specific mine operations are covered in numerous publications produced over the years by the U.S. Bureau of Mines, U.S. Geological Survey, California Division of Mines and Geology (now California Geological Survey), and others. The most recent geologic mapping covering the area is the 1:250,000-scale Chico Quadrangle compiled by Saucedo and Wagner (1992). The local Dutch Flat area was also mapped by Harwood (1980) at moderate scale. Stratigraphy The northern Sierra Nevada basement complex has a history of both oceanic and continental margin tectonics recorded in sequences of oceanic, near continental, and continental volcanism. The complex has been divided into four lithotectonic belts; the Western Belt, Central Belt, Feather River Peridotite Belt, and Eastern Belt (Day and others, 1988). The Western Belt is composed of the Smartville Complex, a late Jurassic volcanic-arc complex (Beard and Day, 1987), which consists of basaltic to intermediate pillow flows overlain by pyroclastic and volcanoclastic rock units with diabase, metagabbro, and gabbro-diorite intrusives. The Cretaceous Great Valley sequence overlies the belt to the west. To the east it is bounded by the Big Bend-Wolf Creek Fault Zone. East of the Big Bend-Wolf Creek Fault Zone is the Central Belt, which is in turn bounded to the east by a fault known farther north of Dutch Flat as the Goodyears Creek Fault. This belt is structurally and stratigraphically complex and consists of Permian-Triassic argillite, slate, chert, ophiolite, and greenstone of the marine Calaveras Complex. The Dutch Flat District is part of this belt, which is underlain here mostly by metavolcanic rock. The Feather River Peridotite Belt is also fault-bounded, separating the Central Belt from the rocks of the Eastern Belt for almost 95 miles along the northern Sierra Nevada (Day and others, 1988). It consists largely of Devonian-to-Triassic serpentinized peridotite and dunite and is just east of the Dutch Flat District. The Eastern Belt, also known as the Northern Sierra Terrane, is separated from the Feather River Peridotite Belt to the west by the Melones Fault Zone of Clark (1960). The Northern Sierra Terrane is primarily composed of siliciclastic marine metasedimentary rocks of the Lower Paleozoic Shoo Fly Complex overlain by Devonian-to-Jurassic metavolcanic rocks. Farther east are Mesozoic granitic rocks of the Sierra Nevada Batholith.

Comment (Workings): Working drifts in the gravel beds and pay leads themselves were larger than the bedrock tunnels and usually timbered due to their extended and long-term use. In wide gravel deposits, as a precaution against caving, gravel pillars from 20 - 40 feet wide were left on each side of the drift. When the main access tunnel was in bedrock following the line of the channel, pillars were not required, as the tunnel in the gravel was only for temporary use in mining the ground between its connections with the bedrock tunnel. Raises to access the gravel were made every 200 - 400 feet as necessary. The breaking out of gravel (?breasting?) was done from the working faces of drifts. Usually, 1-2 feet of soft bedrock and 3-4 feet of gravel were mined out to advance the face. When the gravels were well-cemented, blasting was required. Otherwise the material could be removed with picks. Boulder-sized material was left underground, and only the gravels and fines were removed from the mine. Some mines were plagued by bedrock swelling. Both tunnels on and within bedrock were sometimes affected by the upward swelling of the bedrock. In these cases, heavy timbering was required and the tunnel floor had to be periodically cut and lowered to keep the tunnel open. Soft or fractured slates were the most favorable bedrock. The surface was usually creviced and weathered enough that gold could be found to a depth of one foot in the top of the bedrock. Where sufficiently weathered and soft, this upper bedrock layer could be easily removed. If the surface of the bedrock was too hard to be worked, it was cleaned thoroughly, and the crevices and surface were worked with special tools to remove every particle of gold, before the boulder waste was thrown back on it. According to the hardness of the gravels, they were either washed through sluices or crushed in stamp mills. Most of the lower gravel in the Dutch Flat District was highly cemented and required milling in a stamp mill. Ventilation of mines was accomplished by direct surface connection through the use of boreholes and the mine shafts and tunnels. It relied on natural drafts, drafts by fire, falling water, or blowers. Within the mines, arrangements of doors were often used to direct the flow of air through the tunnels, drifts, and breasts. In most drift mines, ore was removed by ore cars of 1- to 2-ton capacity. Car capacity was largely determined by the available power and tunnel size. In smaller mines, small cars were often pushed by hand. In larger mines using horsepower or trains, larger two-ton cars could be brought out in trains of 5-10 cars.

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References

Reference (Deposit): Brooks, E. R., 2000, Geology of a late Paleozoic island arc in the Northern Sierra terrane, in Field guide to the geology and tectonics of the northern Sierra Nevada, California Division of Mines and Geology Special Publication 122, p. 53-110.

Reference (Deposit): Browne, R. E., 1890, Ancient river beds of the Forest Hill Divide: California State Mining Bureau 10th Annual Report of the State Mineralogist, P. 435-465.

Reference (Deposit): Chandra, D. K., 1961, Geology and mineral deposits of the Colfax and Foresthill quadrangles, California: California Division of Mines Special Report 67, 50 p.

Reference (Deposit): Clark, L. D., 1960, Foothills fault system, western Sierra Nevada, California: Geological Society of America Bulletin, v. 71, p. 483-496.

Reference (Deposit): Clark, W. B., 1966, Gold, in Mineral resources of California: California Division of Mines and Geology Bulletin 191, p. 179-185.

Reference (Deposit): Clark, W. B., 1970 Gold districts of California: California Divisions of Mines and Geology Bulletin 193, p. 49-50.

Reference (Deposit): Crawford, J. J., 1896, Gold in Placer County: California State Mining Bureau 13th Annual Report of the State Mineralogist, p. 272-287.

Reference (Deposit): Day, H.W. and others, 1988, Metamorphism and tectonics of the northern Sierra Nevada, in Ernst, W. G., editor, Metamorphism and crustal evolution of the western United States (Rubey Volume VII): Prentice-Hall, Englewood Cliffs, New Jersey , p. 738-759.

Reference (Deposit): Dunn, R. L., 1888, Drift mining in California: California State Mining Bureau 8th Annual Report of the State Mineralogist, p. 736-770.

Reference (Deposit): Gilbert, G. K., 1917, Hydraulic mining debris in the Sierra Nevada: U.S. Geological Survey Professional Paper 105, 155 p.

Reference (Deposit): Hamilton, F., 1920, Placer County: California State Mining Bureau 17th Report of the State Mineralogist, p. 442-451.

Reference (Deposit): Hammond, J. H., 1889, The auriferous gravels of California: California State Mining Bureau 9th Report of the State Mineralogist, p. 105-138.

Reference (Deposit): Harwood, D.S., 1980, Geologic map of the North Fork of the American River Wilderness Study Area and adjacent parts of the Sierra Nevada, California: U.S. Geological Survey Miscellaneous Field Studies Map MF-1177-A, scale 1:62,500.

Reference (Deposit): Harwood, D.S., 1988, Tectonism and metamorphism in the northern Sierra terrane, northern California, in Ernst, W. G., editor, Metamorphism and crustal evolution of the western United States (Rubey Volume VII): Prentice-Hall, Englewood Cliffs, New Jersey, p. 764-788.

Reference (Deposit): Jarmin, A., 1927, Report of the Hydraulic Mining Commission upon the feasibility of the resumption of hydraulic mining in California: California Division of Mines 23rd Report of the State Mineralogist, p. 45-116.

Reference (Deposit): Jenkins, O. P., 1932, Geologic map of the northern Sierra Nevada, showing Tertiary river channels and Mother Lode belt: California Division of Mines 28th Report of the State Mineralogist, p. 279-298.

Reference (Deposit): Lindgren, W., 1900, Colfax folio, California: U. S. Geological Survey Atlas of the U. S., Folio 66, 10 p.

Reference (Deposit): Jenkins, O. P., 1935, New technique applicable to the study of placers: California Division of Mines 31st Report of the State Mineralogist, p. 143-210.

Reference (Deposit): Merwin, R. W., 1968, Gold resources in the Tertiary gravels of California: U.S. Bureau of Mines Technical Progress Report 3, 14 p.

Reference (Deposit): Saucedo, G. J. and Wagner, D. L., 1992, Geologic map of the Chico Quadrangle: California Division of Mines and Geology Regional Map Series Map No. 7A, scale 1:250,000.

Reference (Deposit): Waring, C. A., 1917, Placer County: California State Mining Bureau 15th Report of the State Mineralogist, p. 309-399.

Reference (Deposit): Yeend, W. E., 1974, Gold-bearing gravel of the ancestral Yuba River, Sierra Nevada, California: U. S. Geological Survey Professional Paper 772, 44 p.

Reference (Deposit): Lindgren, W., 1911, The Tertiary gravels of the Sierra Nevada of California: U. S. Geological Survey Professional Paper 73, 226 p.

Reference (Deposit): Logan, C. A., 1927, Placer County: California Division of Mines 23rd Report of the State Mineralogist, p. 235-279.

Reference (Deposit): Logan. C. A., 1936, Gold mines of Placer County: California Division of Mines 32nd Report of the State Mineralogist, p. 7-96.

Reference (Deposit): Logan, C. A., 1948, History of mining and milling methods in California, in Jenkins, O.P. and others, editors, Geologic guidebook along highway 49 - Sierran gold belt - The Mother Lode Country: California Division of Mines Bulletin 141, p. 31-34.

Reference (Deposit): Beard, J. S. and Day, H. W., 1987, The Smartville intrusive complex, Sierra Nevada, California: The core of a rifted volcanic arc: Geological Society of America Bulletin, v. 99, no. 6, p. 779-791.

Reference (Deposit): Averill, C. V., 1946, Placer mining for gold in California: California Division of Mines Bulletin 135, p. 377.

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California Gold

"Where to Find Gold in California" looks at the density of modern placer mining claims along with historical gold mining locations and mining district descriptions to determine areas of high gold discovery potential in California. Read more: Where to Find Gold in California.