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Mining Glossary

Adit: A horizontal or gently inclined passage leading into a drift or hard-rock mine that follows the auriferous gravels or vein. Containing only one opening, as opposed to a tunnel, which has two. Frequently associated with shafts, adits contrast with cross-cuts. Sometimes, generally used as any horizontal hole into a hill or mountain.

Alluvium: A general term for clay, silt, sand, gravel, or similar unconsolidated detrital material deposited during geologically recent time by a stream or other body of flowing water.

Amalgamation: For gold, the process of pouring mercury into a pan at the end of a day or behind the riffles in a sluice whereby it combines with the gold to form an alloy or amalgam. The next step in the gold-extraction process is retorting, which leaves only the gold behind.

Arrastra: The arrastra is a circular stone-lined mill with a center post and dragstone that pulverized cobble-size consolidated deposits. Once pulverized, mercury was added at the final stage with the slurry released through a small hole (otherwise plugged) after it is run through a rocker, long, tom, or sluice. Water or animal operated, arrastras require very little energy and capital once constructed. Additional gold was recovered from cracks and unchinked spaces in the rock floor. During periodic clean-up events, floors were periodically pulled to replace worn-out floor rocks and to amalgamate any gold that might have collected in crevices. These devices were used beginning in the late 1840s by a large population before the introduction of stamp mills, after which their use gradually declined until the 1940s. After the 1850s, arrastras continued to be used by a few for small-scale individual operations. Similar device is Chili Mill; Spanish spelling is arrastre.

Assay: To test the deposit for the quality and quantity of gold or other valuable substance. Assaying focuses in on specific minerals, such as gold, and does not provide the range of minerals available at a location. Typical for most placer mining operations a prospect pit is dug and the removed earth reduced by panning to determine if ground sluicing or hydraulic mining is practical.

Auriferous: Containing gold.

Bench Placers: These placers are sections of a former stream channel that have been geologically abandoned when the stream changed course or carved down into the hillside. Containing some or all of the characteristics of modern stream placers, bench placers are often a ways from a watersource, 50 to 300 ft. above the present stream placers. Higher locations were sometimes called hill diggings. In California typically smaller ones were ground sluiced and larger ones were hydraulically mined.

Booming: A California term that refers to the collection of water at a reservoir dam and then its sudden release (usually through a gate), eroding and transporting gravel through sluices downstream. The gate allows the process to be repeated once the dam has filled with water. Used in either ground sluicing or hydraulic mining, frequently near the end of a season when water is scarce .

Boulder: Any rock 10 inches long or larger.

Cairn: A group of stacked rocks used to demarcate a boundary. In mining often used to define the boundaries of or denote the general area of a claim.

Claim: The size of ground that one claimant or company is permitted under federal and local laws to mine. Sometimes marked with either rock cairns with the paper documentation inside a can or jar, or after 1905 when pocket-tobacco cans were nailed to trees about five to six feet off the ground. Other examples of claims markers are carved into the wood of trees. Not all mining events had filed claims.

Clean-up: The practice of collecting gold taken out during a single run of a stamp mill, arrastra, dredge, or drift or hydraulic claim.

Cobble: Any rock between 2 ½ and 10 inches long.

Colluvial: An adjective used to describe mixed deposits usually at the foot of a slope or cliff that have been transported mainly by gravity.

Crevicing: The mining of stream channels for gold that has washed down and lodged in bedrock. The best locations are just below fast moving sloping areas at flat areas with tilted bedrock of shale and slate. Picks, pry bars, long-handle spoons, and shovels are used to loosen the detrital material and then it is washed to recover any gold. Frequently this is a spring or summer activity for one or two people, leaving little archaeological remains. Now it is considered recreational, but previously associated with more depressed times or an activity to augment other.

Cross-cut: A horizontal passage dug at right angles to the gold. Also see adit.

Crucible: A stoneware hollow container used for melting or calcining metals, ore, etc.

Cyanide: A metal used in gold extraction. Large, rectangular tin cans that once contained the substance are frequently strewn over the hillside or along creek banks near mill areas.

Dams: A variety of dams were used in mining related activities. Dam walls were constructed from earth, stone, timber, and eventually concrete. In California, there were two main kinds—debris dams and reservoir dams. Small versions of this would include wing dams.

Debris: The silt, sand, and gravel that flows from hydraulic mines.

Debris Dams: These dams were constructed to hold back the hydraulic debris. This was legally mandated to be part of a mining landscape after 1884 in any source that lead to the Sacramento River, or late 1880s in other northern California locations (such as the Siskiyou area). Most often the wall was constructed of logs, bolted and spiked together, which was called a crib dam. This type of construction acted as a sieve allowing water to leak out while keeping the debris contained.

Ditch: A linear structure used to transport water from one location to another. Basic, small, hand-dug ditches are the most common. For these small ones, construction consists of possibly surveying or more probably eyeballing it along a contour. Then vegetation is removed and the ditches are dug by shovels into the hillside packing the removed dirt on the downhill side to create a berm, often incorporating local county rock on steep slopes and in drainages. Larger ones were usually surveyed, and financed and built by a company. Large ones typically contained flume portions and then later siphons, for crossing drainages. Initial ditch building in the Sierras was begun by companies of miners who needed a constant large supply of water to separate out gold through sluicing. The average mining ditch drops 7 to 12 feet per mile.

Dredging: The mining of large alluvial deposits by floating washing machines (dredges) that are either bucket-line or dragline. Both kinds of dredges excavate the gravel, process it, and then expel it into rows of large tailings piles usually away from the dredge pond or working area.

Drift Mining: Employed in California by 1851 (some suggest as early as 1849), a placer mining technique that uses adits to follow the tertiary gravels containing gold. Shafts might be added to bring in air and, depending on the size of the operations, galleries and gangways were also used. When veins or old watercourses were near the surface, miners would uses trenches. After digging the gravels, early drift miners processed the material with a pan, sluice, or long tom. This technique reached its peak in the 1870s and was in use in some localities until World War II. Sometimes called coyoting.

Dry Placer: In arid or semiarid areas, dry placer refers to placer deposits that are transported by erratic, short-lived fast-moving creeks that are a product of heavy raining. The gold is often angular because it has not been tumbled very far or for very long. Usually the water supply must be brought into the workings. Now called Desert placers. Historically, more successful in Australia than in the southwestern United States.

Flood Gold Deposits: Flood gold or flour gold refers to particles of gold so small that they float in muddy water, often traveling long distances under flood conditions before they are deposited between the high and low water level along bars. Panning, or devices with riffles will not profitably capture this type of gold. Early on rockers were modified and used to capture this type of gold, with some dredging operations later in time. Typically such mining is not very profitable.

Flume: A channel usually made of milled wood that was originally constructed to bring water to mining claims. Sometimes used in conjunction with ditches. Later used for agricultural and municipal uses. By 1852, it was cheaper to build flumes than reservoirs, even though lumber was expensive. Two years later it was universally preferred.

Giant/Little Giant/Monitor: Names for nozzles used in hydraulic mining that create the intense pressure necessary to reduce hillsides to gravel.

Grain: Rock material ranging from 1/16 to 1/8” long. Items smaller than this are divided into various kinds of sand, followed by silt and then clay.

Gravel: Any pebble between 1/8 and 2 ½ inches long.

Grizzley: A grate or grill typically made from a series of evenly spaced ferrous bars or rails (typically 2-4 inches wide) sometimes used at the head of a sluice to eliminate large rock (creating placer tailings); or along a sluice to allow smaller cobbles and gravels to pass into an undercurrent for finer sorting.

Ground Sluicing: A mining method that uses water not under pressure to wash away and process placer deposits and overburden. A head race brings water to a workings where either from here or using a hose, penstock, or a lateral ditch the water is allowed to wash over gravels with the encouragement of picking nearby hillside creating a working face. The washed gravels are processed through wooden sluice boxes or narrow rock-line custom-built sluice channels, with larger rock being cast aside end up as either placer tailings or stacked rock depending upon the nature of the operation. Canvas hoses were more flexible and allowed miners to move and point them in different angles to be the most effective, but unlike penstock, the hoses were not as durable.

Head Race: A ditch or flume supplying water to a workings or mill. See supply ditch and lateral race.

Hydraulic Mining: Invented in 1852 and legally restricted in 1884 because of its environmental effects, hydraulic mining involves excavating the bank or hillside for gold-bearing gravel by aiming a high-pressured hose at it. The hillside caves in, disintegrating into gravels, which are carried through sluices where the riffles catch the gold. This process leaves an easily identifiable, devastating, moon-like landscape. After 1884, all hydraulic mining legally needed to include debris dams downstream (or late 1880s for Northern California outside the Sacramento River rivershed).

Lateral Race: A small ditch lying between the main race and a mining operation.

Long Tom: Introduced to California gold fields beginning in 1850. The long tom is two-layered wooden device consisting of an upper trough (8 to 15 ft. long by 1 ½ to 2 ft. wide) with perforations at one end allowing smaller washed gravels and smaller heavy particles to wash into the lower riffled box. Later versions combine the two layers.

Matrix: The rock containing a valuable mineral or metallic ore, such as gold.

Mercury/Quicksilver: A heavy silver-white mineral, mercury combines with most metals (gold, silver, etc.) to create an alloy or amalgams. It is a vapor when heated, and liquid under ordinary temperatures. Its abundance in the western United States, made mercury the preferred way to extract gold from panning and sluicing. See amalgamation and.

Miner’s Inch of Water: A measurement of water volume. Once an arbitrary volume varying by locality that is still not nationally standardized, but defined for each state. In California, a miner’s inch is either 9 (1/40 second-foot) or 11.5 gallons (1/50 second-foot) per.

Open Cut: A surface working that is open to daylight, generally used for gravel or stone work. See also cut and working face.

Ore: A mineral aggregate containing a valuable constituent (such as a metal) which is mined and worked for a profit.

Panning: In use in California by 1848, panning is the earliest and least complicated of all methods with a miner needing a shovel and a flat pan (any dish could be used, even baskets and wooden ones, Euroamericans preferred tin (ferrous) pans with an approximate 10 in. base and gently tapered sides of about 4 in.). The pan allows the gravel to be separated from the gold and the soil by washing this material in a pan with water in a swirling motion. It had widespread used by very early miners in California. By 1849, it was typically used in conjunction with more efficient devices, such as rockers, sluices, and long toms. Its continued use was not as the main method to process gold, but to assay or assess the quality and quantity of gold from a new area and to further process the reduced remains at the end of a day.

Penstock: Wrought-iron heavy-grade sheet metal that was transported to a working, ditch, or flume and then custom built for an individual working or water system. The pipe was placed resting on the ground, buried to last longer, or, when spanning a gulch, supported by a trestle. This is left on site once workings were abandoned. Canvas used first then penstock was introduced and first manufactured and commercially used in California in 1856.

Placer: A gravel deposit containing gold, or other valuable minerals, usually in loose alluvium that can be easily excavated or washed. Placers have been divided into the following classifications: residual placers, eluvial placers, stream placers (including the subcategories gulch, creek, river, and gravel-plain), bench placers, flood gold deposits, desert (dry) placers, tertiary gravels, and miscellaneous types (beach placers, glacial placers, and eolian placers).

Placer Mining: Practice of processing auriferous sediments to extract gold. Typically using water to reduce the volume of placer deposits. Methods include of panning, sluicing, ground sluicing, hydraulicking, and dredging.

Placer Tailings: Any size gravels, cobbles and boulders that are moved in the act of placer mining; typically in piles or stacked. Since this is a generic term, it is important to note the size and origin of the rock, to elaborate on specific placer mining activities.

Pocket Mining: Pocket mining begins with panning a shovelful of dirt from a hillside, looking for isolated surficial veins of gold. When gold is identified, another sample is taken nearby, until a small area is defined or the pocket can be defined. Then a prospect pit was dug and occasionally blasting was necessary. Made famous in Mark Twain’s Roughing It, this method was sometimes called coyoting in California.

Prospect Pits: Holes dug into creek terraces and hillsides with excavated material typically part of the hole’s berm or lying nearby. These are most likely the result of assaying or pocket mining. The slang term is glory hole.

Prospecting: Conducting exploratory excavations; searching for productive placer deposits for new areas to work.

Race: An open channel—ditch —that carries water. There are various kinds of races: head races, lateral races, and tail races are used most often.

Reservoir Dams: Dams constructed to store a constant water source for ground sluicing, booming, and hydraulicking operations. Preferred locations for storage reservoirs are those that contained compact rock and steep, denuded watershed. Masonry dams were expensive to build but at least one side must be stone to successfully hold large amounts of water, with later ones constructed from concrete. Often these have been turned into past of the municipal water system for the county.

Residual Placers: A concentration of gold at or close to the parent rock from which it was released. These deposits are not large, may be rich, and usually considered relatively unimportant.

Retorting: For gold, once amalgamation has been done the process of vaporizing the mercury from the alloy or amalgam so that only the gold remains. A retort is iron bowl with a fitted lid and a pipe leading from it to a container of condensing water.

Riddle: A sieve.

Riffle: A small ridge in sluice-type mining devices to trap the heavier gold while lighter material would be washed away and larger material would be forked out. Sometimes this is as simple as a series of small pieces of wood nailed to the base of a sluice, long tom, or rocker.

River Mining: This mining method consists of temporary diversions of rivers and creeks during the dry season to mine exposed gravels and bedrock for gold. Euroamericans employed diversions consisting of wing dams, ditches, and flumes. In use in California by 1849, this technique peaked in 1855 and 1856, before rapidly declining among Euroamericans. This method was very popular in Butte County. Chinese miners continued to use this technique using a waterwheel pump, which picked up the water and dumped it into a nearby sluice. Occasional later ventures included constructing the 12,000-ft., almost-one-million-dollar Big Bend Tunnel to expose 13 miles of the North Fork of the Feather River.

Rocker: Also called a rocker cradle or miner’s cradle, the rocker is a two-layered wooden box and trough device. Dirt and water pass through the upper box through perforations (or riddle), where the remainder is washed over riffles that catch the gold with the rest washed out the end. The removable top box has a handle. First used in 1848, the rocker was an improvement over panning (four times more efficient) and was popular by everyone in the early 1850s, and continued to be popular with Chinese miners and also where water was limited or in certain seasons. There were variations to the basic design—one was called a bullrocker.

Run: The length of time a mine operates before it is shut down to clean up, repair, or other tasks.

Shaft: A vertical or near-vertical passage used for airshafts (typically smaller) or framed with wood for support for hard-rock mining endeavors. Entrance shafts to hard-rock mines typically involve hoists and their accompanying stone or concrete foundation.

Siphon: A ferrous-pipe system spanning gullies and drainages, that lying down one side of the bank and up the other. This device allows the water to be supplied by gravity and pressure either over or into gullies.

Sluice Channel: Also called sluice water channel, the U- or V-shaped channel typically framed by placer tailings above which a wooden sluice was washed. Also refers to the custom-made, rock-lined versions built into the bedrock often with stacked rock along the sides; these were constructed from the large boulders and cobbles (placer tailings) exposed during that particular location.

Sluices: Sluices usurped the Long Tom and revolutionized gold washing. There were two basic types. Either alone or an interconnecting series of wooden sluice boxes with many riffles or other gold-trapping items crossing its width, through which the earth and water was passed. In a modified version, exposed bedrock from mining operations was dug to create long troughs with the uneven rock acting as riffles. Gravels and cobbles were periodically forked out to keep the path open creating piles of placer tailings and sometimes stacked rock. Sluices were used in sluicing, ground sluicing, drift, and hydraulic mining.

Sluicing: Introduced in 1850, the method used sluices to process creek and creek terrace gravels for gold. Using a high amount of water, sluicing is often associated with ditches bringing water to the workings.

Stamp Mill: First documented use in California was 1851. A stamp mill consists of a vertical steel stem with an iron foot or shoe that is lifted by a cam and dropped with weight and gravity crushing the ore below. Stamp mills vary by the number of stamps and are described as such. Typically surrounded by tailings piles. In gold-rich areas, stamp mills were in use seven days a week, through out the day and night.

Stream Placer: Deposits concentrated in current watercourses. This placer has been further subdivided by landscape form: gulch, creek, river, and gravel-plain placers.
Gulch placers are small in area, steep, and typically limited to minor watercourses. Usually of poorly sorted gravels, they are often thin and discontinuous, surround by large quantities of boulders. In California, usually these areas were mined early on using basic hand tools, with some areas re-mined.
Creek placers were often an important source of gold and have been mined using many methods beginning with panning and continuing through Depression-era re-mining dredging events.
River deposits usually constitute the most extensive and important areas to be worked. These overall low-grade deposits have spurred river mining and dredging sometimes with very high yields.
Gravel-plain or bar placers are formed or large rivers during times of high water creating geographic features frequently named flats, bars, or gravel bars. Ranging in age from geologically old to recent, they are found in flat areas of rivers just beyond steep drop offs and the inside curve of a gooseneck. Similar to river placers, the gold deposit tends to be larger in size with higher gold yields.

Strip: To remove overlying earth, low-grade or barren material from a placer deposit.
Supply Ditch: A ditch that carries water to the general area of a mine or group of mines, but cannot be specifically called a head race.

Tail Race: The channel at the end of a sluice containing water and tailings, most of which gets carried downstream.

Tailings: The materials washed and expelled out at the end of a gold-processing device. See placer tailings and debris.

Tertiary Gravels: Gold-bearing gravels from Tertiary age (60 to 1 million years ago) stream alluvium.

Undercurrent: This labor saving device consists of a flat, broad wooden box or stone sluice channel, platform below and angling to the side of any sluice-type device with a grizzley. Also containing riffles, the undercurrent washes water over the smaller cobbles and gravels that fall through a grizzley. At a steeper slope that the main sluice (typically 1 to ½ in. per ft.), the undercurrent is not only faster, but more profitable in recovering more of the gold than that of a sluice. It is in this portion of the device that the gold will be amalgamated.

Waste Rock: Barren or marginal rock that has been excavated but not of sufficient value to warrant milling; rock not valuable enough to be classified as ore. Also called waste.

Wing Dam: Employed in river mining, a wing dam is somewhere between a dam and a flume system. The wing dam is L-shaped, extending out from the creek bank and into the middle of the stream channel, and then angling upstream. Typically built from stacked stone with brushed packed with soil to cover it. The result leaves part of the riverbed exposed.

Working Face: Any portion of a claim where work is underway.

Recommended References

Bates, Robert L. and Julia A. Jackson, editors
1984 Dictionary of Geological Terms. Anchor Press, Garden City, New Jersey.

Boericke, William F.
1936 Prospecting and Operating Small Gold Placers. John Wiley & Sons, Inc., New York, London, & Sydney.

Bowie, A.J.
1910 A Practical treatise on Hydraulic Mining in California. D. Van Nostrand Co., New York.

Brererton, Roslyn
1976 Mining Techniques in the California Goldfields During the 1850s. Pacific Historian 20(3):286-302.

Degroot, Henry, Sr.
1881 Glossary of Terms in Common Use Among the Miners of California. Annual Report of the State Mineralogists, June 1, 1880 to December 1, 1880:280-288.

Fay, Albert H.
1920 A Glossary of the Mining and Mineral Industry. Bulletin 95. Department of the Interior, Bureau of Mines, Government Printing Office, Washington.

International California Mining Journal
2004 Dictionary of Mining Related Terms. International California Mining Journal. Available at

Jenkins, Olaf P.
1946 New Technique Applicable to the Study of Placers. California Division of Mines Bulletin 135:149-216.

Natural Resources Conservation Service
2004 NSSH Part 629 – Glossary, A-C. Natural Resources Conservation Service. United States Department of Agriculture. Available at

Wells, John
1969 Placer Examination, Principles and Practice. Bureau of Land Management, United States Department of the Interior, Technical Bulletin 4. Washington, D.C.

Wilson, Eugene B.
1907 Hydraulic and Placer Mining. Second Edition. John Wiley & Sons, New York.