Michigan Bluff Mining District (Michigan Bluff Mining deposit), Placer County, California, USAi

Regional Level Types
Michigan Bluff Mining District (Michigan Bluff Mining deposit)	Mining District
Placer County	County
California	State
USA	Country

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Location: The Michigan Bluff district is a former Au-Ag-Pt-Cu-Zn-Fe-Pb-In mining area located in secs. 3-5, T13N, R11E, and in secs. 2, 3, 9-11, 14-17, 20-23, 26-29 & 32-35, T14N, R11E, MDM, in southcentral Placer County, 5 miles E of Foresthill. Discovered in 1850. It is best known as a placer mining district, and includes the Turkey Hill, Byrd's Valley, and Baker Ranch areas. The Damascus district is to the north and the Forest Hill district is to the west.

The Michigan Bluff District includes a number of individual mines distributed throughout an area encompassing approximately 18-20 square miles. Since the majority of mines and claims were located around the community of Michigan Bluff, the community itself was chosen to represent the district's location. The location latitude and longitude identify the intersection of Michigan Bluff Road and Gorman Ranch Road near the center of town on the USGS Michigan Bluff 7.5-minute quadrangle (within the W½W½, sec. 22, T14N, R11E, MDM). Michigan Bluff is reached by taking the paved Foresthill Road from Auburn, California, for a distance of about 25 miles, then turning south on the paved Michigan Bluff Road and continuing on for an additional 3 miles.

The district includes all placer and quartz gold mines in the Byrds Valley and Chicken Hawk Ridge areas from Baker Ranch on the west to approximately 2 miles east of Michigan Bluff, and between the Middle Fork of the American River on the south and the Gas Hill Mine on the north. The Gas Hill Mine (sec. 2, T14N, R11E, MDM) marks the southern limit of the adjacent Damascus Mining District to the north. The Forest Hill and Last Chance mining districts lie to the west and northeast, respectively. The district trends northeast-southwest along the crest and southeast flank of the Forest Hill Divide, a northeast-southwest trending drainage divide separating the North and Middle Forks of the American River. The district is primarily a placer-gold district, the majority of production having come from drift and hydraulic mining of Tertiary gravel deposits. Very little was produced from gold-quartz lode mines within the bedrock complex.

History: The town, first settled in 1850, was originally known as Michigan City. In 1858 the land began to slide into the river, so the town was moved higher up on the mountain side and became Michigan Bluff. Hydraulic mining began here in 1853, and the district soon became highly productive. During the middle and late 1850's, the gold output averaged $100,000 (period values) per month. Leland Stanford, Governor of California, and one of the builders of the Central Pacific Railroad, operated a store here from 1853 to 1855. His old home still stands. Activity in the area declined during the 1870's, but some work continued intermittently through the early 1900's and again in the 1930's. Much of the region was devastated by fire in 1960.

Miscellaneous Comments: Shortly after the discovery of gold in the American River at Sutter?s Mill in 1848, placer deposits were discovered in the North and Middle Forks of the American River flanking the Forest Hill Divide. Miners soon realized that much of the gold was eroded from rich Tertiary channel gravels perched high on the flanks of the divide. In 1850, the first ancient channels and gravel benches were identified hundreds of feet above the current rivers. In the same year, the community of Michigan City was settled just above an exposure of auriferous quartz gravel on a bluff overlooking Eldorado Canyon on the south flank of the divide. One of the early residents of Michigan City was Leland Stanford, future Governor of California and a founder of the Central Pacific Railroad. Having arrived in 1852 as a miner, he quickly opened a general store then served as justice of the peace before moving to Sacramento in 1855.

The Michigan Bluff gravels were first worked on a small scale by drift mining. Hydraulic mining of the deposits commenced in 1853 and continued until 1883. During the 1850's and 1860's Michigan Bluff was one of the most prosperous camps on the Forest Hill Divide and one of the foremost placer mining districts in the county. Between 1853 and 1858, gold shipments reportedly ran as high as $100,000 a month. In 1857, Michigan City was destroyed by fire, but the town was quickly rebuilt only to be moved again when, in 1858, the extensive workings on the bluff below caused the townsite to settle and slide downhill. A new townsite was selected farther uphill, and by 1861 most of the town was relocated and renamed Michigan Bluff (Clark, 1970). Activity began to taper off after 1870, but some work continued intermittently through the early 1900's and again in the 1930's. By 1880, most of the smaller hydraulic claims covering the bluff had been bought by the Big Gun Mining Company and consolidated with the Big Gun Mine, which was reported to have produced $1 million by 1882 and continued to operate sporadically until 1900.

The extensive hydraulic workings at Michigan Bluff and elsewhere in the Sierra Nevada dumped enormous quantities of sediment that choked local streams and eventually affected the Sacramento River. This waste resulted in extensive flooding and silting of downstream farmlands and litigation between the farming and mining interests. In 1884, the resulting Sawyer Decision injunctions, which curtailed sediment dumping in rivers, precipitated a plunge in hydraulic mining activity. Hydraulic mining so declined that by 1908, the total production of hydraulically mined gold in California had declined to $170,000 (Lindgren, 1911).

Miners persevered by following the richest auriferous channel gravels underground by drift mining. Generally, only the basal Eocene gravels were rich enough to warrant drift mining, but several intervolcanic gravels including those of the Orono Channel were found to be profitable by drift mining.

The most significant drift mines in the Michigan Bluff District were the Turkey Consolidated and Hazard Mines. While no date of discovery is known, the Turkey Consolidated Mine started out as the independent Boston, South Dakota, Weske, and Manhattan claims, which were later consolidated. The main drift was originally driven on the Weske claim in the Orono (Weske) Channel. The channel was mined for more than a mile west from a portal on the east side of Chicken Hawk Ridge. A second intervolcanic channel was drifted on the neighboring Manhattan claim where the Manhattan Tunnel was driven approximately one mile north with limited results.

By 1917 very little production was coming from the mines in the Michigan Bluff District, and dredging on the Middle and North Forks of the American River had become the primary means of gold recovery in Placer County. Only a few small placer mines were producing in the Michigan Bluff District. These included the Bogus Thunder and De Maria mines. Several small drift mines were also reportedly still in operation doing assessment work, but none was producing. These mines included the Franklin Drift, Golden Sheaf Drift, Gorman Drift, Marian Drift, Swift Shore Drift, and the Turkey Hill Consolidated Drift. Quartz mining, was also dormant with only a few mines conducting assessment work. These included the Bunker & Nihill Quartz, Champion Quartz, and Daniel Webster Quartz mines.

The district saw a little activity during the Depression, but interest waned by the1940s. Operation of all mines ceased in 1942 with the War Production Order. No mines are active today.

Today, little visible evidence remains of Michigan Bluff's heydays. While the remains of some of the hydraulic mining operations are visible, the remains of the drift mines are far from evident to the casual observer. Since virtually all former drift mines are on posted private property, permission must be obtained to access these sites.

Geology: This district is at the junction of two major Tertiary channels, one that comes in from the north from the Damascus district and the other comes in from the southeast from Ralston Divide. Just to the north at Baker Ranch there is an intervolcanic channel. The lower gravels at Michigan Bluff are nearly pure quartz with many large boulders. The gravels were extremely rich, the gold yield from six million cubic yards reportedly having been $5 million (period values). Much of the gold was coarse. Bedrock is slate and schist, and to the west there is serpentine. Some narrow gold-quartz veins are present.

The Michigan Bluff deposit is synonymous with the Michigan Bluff District. The district is primarily a placer gold district, the bulk of its production coming from just a few important hydraulic and drift mines. Many lesser hydraulic and drift mining operations are scattered throughout the district, but did not significantly contribute to the district's output. Of lesser importance yet were a few small, scattered lode mines. The majority of the district's production has come from hydraulic and drift mining operations within a series of buried Tertiary auriferous gravel-filled channels.

Rocks of the Michigan Bluff District can be divided into four units, which consist of basement complex, Eocene auriferous gravels, interbedded volcanic rocks and gravels of the Valley Springs Formation, and an uppermost Mehrten Formation volcanic cap.

The main body of basement rocks within the district is the north-northwest-trending Feather River Peridotite belt comprised of a 1 to 3 mile wide belt of partially to completely serpentinized peridotites. The Feather River Peridotite Belt coincides with the northern extension of the Melones Fault Zone of the Sierra Nevada Mother Lode (Clark, 1960). The Volcano Canyon Thrust Fault forms the eastern boundary of the belt where sandstone, siltstone, and slate of the Shoo Fly Complex are juxtaposed against ultramafic rock and serpentinite on the east side of the district. On the western side of the district, rocks of the Feather River Peridotite belt are faulted against metavolcanic rocks and slate of the Calaveras Complex.

Basal Eocene Auriferous Gravels:

The Michigan Bluff District is at the intersection of two major Eocene channels. The primary channel entered from the southeast from the Ralston Divide District about 15 miles away. A smaller tributary channel entered the district from the Damascus District to the north (Lindgren, 1911) where it was highly productive. Within the district, however, the tributary deposits have been largely lost to erosion.

The Eocene drainage system included an ancient counterpart to the current Middle Fork of the American River, which followed the same general course as the modern drainage. It flowed westward through the Ralston Divide District and skirted the southern part of the Michigan Bluff District where its gravel deposits were discovered on Michigan Bluff. Between the two districts the channel has been lost to erosion. West of Michigan Bluff, the channel has again been eroded, but reappears in the Paragon Mine in the Forest Hill District where it is known as the Forest Hill Channel.

The main gravel deposits in the district are those at Sage Hill and Michigan Bluff adjacent to and below the Michigan Bluff townsite. The gravel exposure at Michigan Bluff covered approximately 40 acres and proved to be one of the most valuable deposits in the district. By 1880, almost all the smaller claims on this deposit were consolidated by the Big Gun Mining Company and operated as the Big Gun Mine, which ultimately produced $1 million (period values) by 1882. This deposit has been correlated with the Eocene Forest Hill Channel in the Forest Hill District to the west and the Long Canyon Channel to the east in the Ralston Divide District. In the Forest Hill District, it can be traced for almost 6 miles and produced more than $6.1 million (period values) from the district's three main mines, the Paragon, Mayflower, and Dardanelles. Channel morphology is characterized by a flat, trough-shaped channel depression incised in bedrock. Where best exposed at the Paragon Mine near Bath, the bedrock channel was 500 feet wide and 100 feet deep. The bedrock surface is irregular with ridges, swales, and potholes conducive to trapping placer gold. In contrast to the equivalent gravels in the Forest Hill District, which are generally a blue-gray due to a concentration of slate and other metamorphic rock, the Michigan Bluff and Sage Hill gravels are almost exclusively white quartz gravels with some white quartz boulders of up to 20 tons. This difference is likely due to their location upstream of Calaveras Complex bedrock and/or to the loss of the deeper thalweg deposits to erosion south of Michigan Bluff. The Michigan Bluff gravels appear to be channel rim and bench gravels deposited along the north side of the old Forest Hill Channel. The quartz gravels are less-cemented and generally do not require crushing. The gravels were said to be as much as 80 feet thick, but averaged 40 feet. Reportedly, some 6 million cubic yards of gravel were hydraulically mined from the Sage Hill and Michigan Bluff exposures yielding approximately $5,000,000 (period values).

A tributary of the Forest Hill Channel flowed southward from the Damascus District and appears to have merged with the main channel near Michigan Bluff. Unfortunately, throughout most of the district its deposits have been removed by erosion in Eldorado Canyon. They are, however, present at the Gas Hill Mine (Sec. 21, T14N, R11E) on the southernmost edge of the Damascus District. Here, the gravels are almost identical to those at Michigan Bluff. North of this mine, the channel is truncated by a deeper intervolcanic channel, but reappears one mile farther north in the Hidden Treasure Mine (Sec. 35, T15N, R11E), where it was called the "White Channel" and produced over $4 million (period values). From the Hidden Treasure Mine, the tributary can be traced almost continuously to Damascus (Lindgren, 1911), a distance of almost 4 miles. The channel is a wide, flat depression in soft, swelling clayey slate bedrock, which required substantial timbering to keep the tunnels open. The channel was filled with almost 200 feet of uncemented quartz gravel, sand, and clay with some quartz boulders. The gravel is markedly finer and more quartzose than that in the Forest Hill Channel to the west. Breasting could be done with pick, and caving and blasting were limited to the removal of some large boulders. In places the channel widened to 800 feet, with rims rising gradually to 16 feet above the thalweg. The width of the gravel breasted was 250 feet, and 4 to 7 feet of the lowermost gravel, including 1 foot of bedrock was extracted. The gold was generally coarse, with gravels yielding only $0.50 to $1.75 (period values) per ton. Only the unusually low cost of production allowed this mine to profitably produce this grade of material via drift mining.

The exact location of the confluence of the Forest Hill Channel and the tributary remains unclear having apparently been lost to erosion south of Michigan Bluff. While the Michigan Bluff gravels resemble more closely those of the tributary in terms of texture, lithology, and yield, they are also consistent with flanking bench gravels of the Forest Hill Channel.

Valley Springs Intervolcanic Channels:

Overlying the Eocene channels are varying thicknesses of intercalated rhyolite tuff and intervolcanic channel gravels (often called ?cement? channels) of the Valley Springs Formation. Toward the top of the formation the tuffs become progressively more andesitic. The thickness of the sequence is highly variable. Thicknesses of up to several hundred feet of gravel, sand, and pipe clay, can extend well beyond the limits of the lowermost bedrock channel depression. Little information is available regarding specific thicknesses within the Michigan Bluff District, but in neighboring Forest Hill District, exposed thicknesses of rhyolite tuff and intervolcanic gravels range from 40-130 feet.

The network of intervolcanic paleochannels is complex, each channel representing a periodic displacement of the stream, a distinct cut with a deposit of gravel, and finally a volcanic event that filled the cut and buried the gravel. The frequent diversion and reestablishment of the intervolcanic channels, and subsequent erosion of earlier channels makes it very difficult to correlate these channels with any certainty. Intervolcanic period channels were deposited during a period of increasing gradient and are characteristically narrower and deeper, the flanks steeper, and the accumulations of bedrock gravel significantly less than those of the older basement channels. Gravel thicknesses in the smaller of these channels are generally several inches to fifteen feet and are generally dominated by volcanic gravel unless that stream cut deeply enough to erode older deposits or basement.

Many intervolcanic channels eroded deeply into older auriferous gravels either partially or wholly destroying them. The Forest Hill Channel is commonly cut by intervolcanic channels, in which case the channels are locally rich in gold. Clay beds are common in the upper portions of intervolcanic gravels. Petrified and/or lignitized cedar and oak tree trunks are not uncommon. Some gravel layers have become highly cemented by percolation of siliceous and calcareous waters, and colors range from gray, blue, reddish brown, to white depending on the source material and oxidation of the gravel and/or cementing material.

The most important intervolcanic channel in the district is the equivalent to the Orono Channel of the Forest Hill District. In that district, it could be traced for almost 14 miles; locally it cut the Forest Hill Channel deposits in the Paragon, Mayflower, and Dardanelles mines. The Orono Channel was found to be particularly rich downstream of those areas and was often worked in lateral drifts from the main Forest Hill Channel drifts.

The Orono Channel can be traced upstream from the Forest Hill District, across Volcano Canyon to the Michigan Bluff District where almost 3 miles of the channel are preserved. From its inlet in Eldorado Canyon, which was drifted in the Weske Tunnel, it trends almost a mile west before tuning sharply south for one mile. It then turns west again and can be traced to Volcano Canyon where it was drifted 3,000 feet upstream in the Hazard Mine. Called the "Weske" channel in the Weske Tunnel, it was drifted downstream for over 5,000 feet, requiring pumps and stopes. The channel was about 100 feet wide and cut into bedrock for most of its mined length. The channel gradient was steep, with many steep drops and potholes (Lindgren, 1911). The thin gravel was overlain with volcanic tuff in which were found several tree trunks in an upright position.

A smaller intervolcanic channel crosses the Orono Channel near the mouth of the Weske Tunnel and trends about one mile northward. Locally dubbed the Manhattan Channel, it was filled with heavy volcanic gravel and was little worked with the exception of a short drift in the Manhattan Tunnel.

Several other fragments of intervolcanic channels are also present, but are too small or erratic for accurate correlation. North of the Weske Tunnel, one short segment of a channel was worked in the Oro and Bowen tunnels. Along the face of Eldorado Canyon are several isolated gravel hills, the relicts of a complicated intervolcanic channel system. These deposits were hydraulically mined at Drummond Point, Eldorado Hill, and Bachelor Hill.

The Valley Springs intervolcanic channel sequence is capped by andesites of the Mehrten Formation in the northwest corner of the district and locally at Sage Hill and Michigan Bluff. It consists of hard and dense massive layers of light gray, reddish brown, and dark colored andesitic mud flows, tuffs, breccias, and volcanic conglomerates.

Lode Gold Deposits: The Michigan Bluff District also contains a few small lode gold mines, such as the American Bar Quartz (sec. 33, T14N, R11E), Champion Quartz (Sec. 15, T14N, R11E), Bunker & Nihill Quartz (Sec. 22-T14N, R11E), and Daniel Webster Quartz (Sec. 33, T14N, R11E). In the Champion and Daniel Webster mines, workings were limited to a few hundred feet of tunnels. The American Bar Quartz Mine is reported to have had total workings of 1,950 feet of tunnels. No information is available regarding the extent of the Bunker & Nihill Mine. The gold-quartz veins were of limited extent and thickness. Veins trended northwest and northeast dipping steeply to the east. The pay occurred as free-milling gold in white mesothermal quartz veins 2 to 5 feet thick within slate with varying amounts of associated sulfides, especially galena. No production information is available for any of the mines

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 Michigan Bluff District.

Ore Bodies/Mineralogy: Mineral occurrence model information: Model code 119; USGS model code: 39a; BC deposit profile: C01. C02; Deposit model name: Placer Au-PGE; Mark3 model number: 54. Model code: 273; USGS model code: 36a; Deposit model name: Low-sulfide Au-quartz vein; Mark3 model number: 27. Host rocks include Tertiary unconsolidated sand & gravels; Tertiary rhyolite tuff; Permian-Triassic Calaveras Complex slate; and Paleozoic serpentinite. Local alteration is negligible (none described). Ore bodies are irregular, tabular, lenticular. Controls for ore emplacement included mechanical accumulation on irregular natural bedrock riffles and within river and stream channel lag gravels, bars, and point bar deposits. Deposits are often enriched downstream of eroded gold quartz veins in the bedrock channels. Ore shoots occur within mesothermal gold-bearing quartz veins. Local rocks include Tertiary pyroclastic and volcanic mudflow deposits, unit 9 (Cascade Range).

Regional geologic structures include the Melones Fault Zone. Local structures include the Volcano Canyon Fault and the Melones Fault Zone.

Commodity Information: Placer deposits: Placer gold dust to large nuggets; Lode deposits: free-milling gold-bearing quartz veins. Ore materials: native gold; gangue materials: quartz gravels; quartz.

Mining Methods

Hydraulic Mining:

Hydraulic mining allowed the bulk processing of large volumes of low-yield gravels that would otherwise prove unprofitable by other methods of mining. Hydraulic mining methods were first applied to the gravels in the Michigan Bluff District in 1853. Crudely applied at first, it evolved to a point where a powerful stream of high- pressure water was directed through large monitors 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 mined in two or more benches. Often, adits were driven into the exposed face and crosscuts parallel to the face were loaded with dynamite to help break down the exposure. The loosened gravels were then washed through long sluice boxes lined with riffles or over 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 as well as dams, pipes, and tunnels. Another costly undertaking was 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 valley. Hydraulic mining flourished for about 30 years until the mid-1880s when the Sawyer Decision curtailed debris disposal.

The primary hydraulic mining operations in the Michigan Bluff District were on the bluff just below the town of Michigan Bluff. Several smaller operations originally worked these deposits, but they were ultimately consolidated as the Big Gun Hydraulic Mine (Secs. 22, 27 T14N, R11E). Smaller-scale operations were conducted on isolated deposits along Eldorado Canyon at the Batchelder Pit (Sec. 11, T14N, R11E), Drummond Pit (Sec. 15, T14N, R11E), and Eldorado Hill (Secs. 22, 23, T14N, R11E).

Drift Mining:

Drift mining in the Michigan Bluff District was not as extensive as in the neighboring Forest Hill or Damascus districts. However, a few significant drift mines including the Hazard and Weske were developed in the intervolcanic Orono Channel. 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 led to all the major 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 usually 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.

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 to 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 to 400 feet as necessary.

The breaking out of gravel (?breasting?) was done from the working faces of drifts. Usually, 1 to 2 feet of soft bedrock and 3 to 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 gravels in the Michigan Bluff District were not highly cemented and did not require milling. Instead, most surface works consisted of no more than a dumping and slaking area, riffled sluices, and a water supply under low pressure. Mercury was added for amalgamation.

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.

Noteworthy Mines:

Unlike the neighboring Forest Hill District in which there were a number of significant mines, the Michigan Bluff District was largely composed of many small mines and claims, some of which were consolidated into only a few significant mines. Consequently, there is very little specific information available about the district's mines.

Big Gun Mine (Sec. 22 & 27, T14N, R11E): Drift and hydraulic mining on Michigan Bluff began in 1853 as a series of small operations on independent claims. In the early years, over 20 claims were worked profitably including the Big Gun, Thompson & Powell, Red Hill, North American, and Van Emon Placer Mines. By 1858, the hydraulic workings on the bluff below the town were so extensive that they undermined the town causing it to settle and slide downhill. The community had to be rebuilt farther uphill in 1861. In 1867, with the introduction of nitroglycerin, blasting was introduced to the hydraulic operation and is said to have resulted in as much work being done by 15 men as had previously been done by a crew of 28. By 1880, most of the smaller claims were bought by the Big Gun Mining Company and consolidated as the Big Gun Mine. The company used 400 inches of water under a 300-foot head. While reliable estimates of early production are lacking, it is estimated that the consolidated Big Gun Mine had produced $1 million (period values) by 1882. Hydraulic mining ceased in 1883. The mine was again operated intermittently between 1896 and 1900 with permits from the California Debris Commission; however, no production records are available for this period. As late as 1926, estimates of as much as 2,000,000 cubic yards of unworked gravel are said to have remained, with negotiations in progress at the time to reactivate the mine (Logan, 1927). No records of any subsequent activity could be found.

Hazard Mine (Sec. 20, T14N, R11E): The intervolcanic Orono Channel was drifted in the Hazard Mine for about 3,000 feet from a 180-foot bedrock shaft on the east side of Volcano Canyon. Other than the channel being narrow with some rich gravel deposits, no additional mine-specific information is available. However, based on information from the Baker Divide Mine on the opposite side of Volcano Canyon, the Orono Channel in this area usually measured 30 to 40 feet wide, but narrowed to 8-10 feet in places. The gravel was 6 inches to 3 feet thick. The yield of the gravel was in part dictated by the hardness of the bedrock. The best pay was found where the channel crossed the softest bedrock.

Turkey Hill Consolidated Mine (Secs. 9, 10, 15, T14N, R11E)

The Turkey Consolidated Mine includes the earlier Boston, South Dakota, Weske, and Manhattan claims. The primary drifting was done in the Orono intervolcanic channel, which was locally called the Weske Channel for its workings in the Weske Tunnel. The Weske Tunnel was driven more than one mile west from a portal on the east side of Chicken Hawk Ridge. The tunnel was driven in bedrock for about 1,500 before breaking into channel gravel. The bedrock gradient was steep, with many steep drops and potholes. The channel itself was drifted downstream, which necessitated the use of pumps and stopes. The gravel channel was 100 to 300 feet wide, and the gravel was generally thin and overlain by volcanic tuff in which were found several tree trunks in an upright position. Approximately 4,000 feet from the portal, an incline was driven downstream into the neighboring Muir claim. The Weske Tunnel itself is reported to have produced $750,000 (period values) by 1911 (Lindgren, 1911). The mine was fully equipped with a surface plant and a locomotive for hauling ore trains.

A smaller intervolcanic channel crossed the Orono Channel near the mouth of the Weske Tunnel and was drifted about one mile northward in the Manhattan Tunnel. Locally called the Manhattan Channel, it was filled with heavy volcanic gravel. No detailed records of the workings or production are available.

Production Information:

In the Michigan Bluff District, it has been estimated that hydraulic mining of Sage Hill and Michigan Bluff worked approximately 6 million cubic yards of gravel and yielded $5 million (period values); the Big Gun Mine alone reportedly produced $1 million (period values) by 1882 (Logan, 1936). At the Big Gun, it has been estimated that as much as 2,000,000 cubic yards of unworked gravel remain (Logan, 1927). By some accounts, Michigan Bluff is considered to have also included some of the most profitable drift mining in terms of yield. In one case, two men were reported to have recovered 1,200 ounces of gold during one week of drift mining. On the Franklin claim, 2,000 square feet of drifting produced $37,000 (period values) (Logan, 1936).

Since production figures were not compiled during the most prolific production years (1852-1884), no accurate figures are available for most of the mines on the Forest Hill Divide, or collectively for the Tertiary channels of the Sierra Nevada. Lindgren (1911) conservatively estimated that approximately $507 million had been produced from Tertiary channels statewide by 1911.

Merwin (1968) concluded that the 1884 Sawyer Decision's adverse impact on hydraulic mining resulted in more than half of the then known gravels statewide being left unworked. He characterized these gravels as one of the largest known reserves of gold in the United States. Based on Gilbert's (1917) volumetric calculations of produced Tertiary gravels, Lindgren's (1911) production information, and average yield information, Merwin estimated that a total of 3-4 billion cubic yards of gravel with an average yield of $0.25/yard and worth $750 million - $1 billion dollars (at $35.00/ounce) remained; the majority of this volume of gravel was contained in the deposits of the ancient Yuba and American Rivers. At today's price of approximately $300/oz this estimate equates to $6.4 to $8.6 billion. His estimate did not include allowance for unknown channel segments of possible value of which we know nothing and which still remained concealed under the volcanic cover.

Mines: Placer: Argonaut & Sunset, Adams, Anna Sue, Baker Divide, Baker Ranch, Beehive, Big Gun (Michigan Bluff) ($1 million+), Bogus Thunder, Boston, Bowen, Bower, Britt, Buckeye, Burnham, Burns, Burroughs, De Maria, Drummond, Eastman, El Dorado Hill, Franklin, Georgia Consolidated, Golden Chief, Golden Gate, Golden Gem Placer, Golden Sheaf, Gorman, Hazard, Hermit, Hoffman, Horseshoe Bar Placer, Imperial, Lightfoot, Manhattan, Marian, Mary Anna, Mountain Chief, Muir Tunnel Consolidated, North American, Oro, Pleasant Bar, Rainbow Land, Red Hill, Russel, Sage Hill, South Dakota, Swift Shore, Thompson & Powell, Turkey Hill Consolidated, Van Emon, Washburn, Washington, Weeks, Weske, Wills & Volcano. Lode: American Bar Quartz, Bunker Hill and Nihill (Bunker & Nihill Quartz), Champion Quartz, Daniel Webster Quartz, Golden Sheaf Quartz.

Commodity List

This is a list of exploitable or exploited mineral commodities recorded from this region.

Mineral List

Mineral list contains entries from the region specified including sub-localities

11 valid minerals.