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Humboldt County

  • Humboldt County Mines and Mineral Resources (circa 1913-1914) - Excerpts from Report XIV of the State Mineralogist - Mines and Mineral Resources of Portions of California, Chapters of State Mineralogist's Report - Biennial Period 1913-1914, Part III. "The Counties of Del Norte, Humboldt, Mendocino," by F. L. Lowell, Field Assistant (field work in September, 1913), San Francisco, California, July, 1915, California State Mining Bureau, San Francisco, California, 1916, pp. 173-370.

    Brief Geologic Description of Del Norte, Humboldt and Mendocino Counties.

    "In discussing the geology of this section of the Coast Ranges, one is confronted with the similarity of the character of the rocks of the different geological ages and the scarcity of fossils by which the different series of stratified rock may be distinguished. The rocks of the different formations have undergone such metamorphism that it is at times difficult to detect the change from one series to another. The Coast Range has been subject to so much disturbance that the rock masses have been crushed and faulted out of their original stratigraphic positions.

    "Beginning at the northern boundary of Sonoma County and extending north through Mendocino, Humboldt, and Del Norte counties, the geological structure is very regular. The rocks are mostly of cretaceous age and are often very much altered. Serpentine, jaspers and mica slates are encountered in large quantities and in a very irregular manner. There are but few areas of unaltered strata.

    "The general strike of the axis of the Coast Ranges through these three counties is northwest and southeast and the preponderance of dip is toward the southwest, the crest of the range being nearer the eastern slope. The deep valleys have been eroded by the abundance of water and the level valleys of some of the watersheds contain strata of Pliocene age. These strata are shallow, and fossils have been noted in Del Norte and southern Humboldt counties. The Tertiary rocks are not as prevalent as those of the Cretaceous. The latter are to be noted more particularly in the oil field region of southwestern Humboldt County.

    "The South Fork of the Trinity River takes the same general northwest direction as the other rivers of the Coast Range. Trinity River changes its direction, flowing nearly west from Weaverville in Trinity County to where it joins the South Fork thence northwest through the mountains to the coast. The Trinity Mountain ranges seems to be the joining strip uniting the main Sierras and the Coast Range. The rocks in this northern section become more crystalline, and the old granites which form the nucleus of the Sierras make their appearance. This granite outcrops north of Humboldt Bay and thence north to the state line.

    "From the junction of the Klamath and Trinity rivers, extending northward to the northern end of Del Norte County, the country is very rugged and covered with forests. The rocks resemble those of the Sierras and are auriferous and cupriferous. The gravels of the rivers also carry gold and platinum values. In this northern region, serpentine is the principal rock. Peridotite, the parent rock of serpentine, is found exposed by erosion on Horse Mountain in northeastern Humboldt County.

    "It might be said that the greater part of the geological formations of Mendocino, Humboldt and Del Norte counties is composed of sedimentary rocks of Tertiary and Cretaceous age. There does not appear to be a nucleus of igneous rock forming the axis of the range, although granite does outcrop in some parts of this section. There are remains of volcanic activity in the form of volcanic glass and tuff, and solfataric action is still taking place at some of the springs of southern Mendocino County.

    "Throughout Mendocino and southern Humboldt counties the Cretaceous sandstones are abundant, being very noticeable at Point Arena and in the oil section of southwestern Humboldt. Organic remains are absent except in a very few instances. The rocks of this age have been altered to a considerable extent and serpentines and mica slates are the alteration products.

    "In Del Norte County, granite forms the nucleus of the mountain ranges and over it is a mantle of metamorphic rocks. In the western portion of the country sedimentary rocks prevail. Intrusive serpentine carries the copper and chrome iron deposits. Quartz occurs in small seams and veins. Copper occurs in lenses of a rich concentration, either as free metal or in sulphides. The slates carry many thin seams of quartz, sometimes rich in gold, and no doubt the erosion of these formations is responsible for the gold concentrated in the streams.

    "This serpentine belt continues through Humboldt and Mendocino counties. Perhaps the most noticeable occurrence is at Horse Mountain, in Humboldt County. There the copper deposits in serpentine are encountered again. The country has been eroded so extensively that the older crystalline diorites protude (sic) through the most recent rock formations. Other acid rocks, such as quartzite, outcrop in large masses, besides a dike of porphyry which forms a well defined contact with serpentine. Not far from Horse Mountain on Willow Creek a large body of limestone is exposed, having a northwest strike. It resembles that in western Trinity County. another limestone formation north of Humboldt Bay is well exposed. The granite formation also outcrops here.

    "Passing south through Humboldt County and across the redwood belt, the later formations of sandstone and shale come in. These carry the oil and gas of this section. The formation is very badly broken up and seepages of oil, and gas emanations are numerous. This formation continues into Mendocino County and is most noticeable on the coast at Point Arena. In the southern portion of Mendocino County, the amount of alteration by the introduction of magnesian combinations is noticeable. This is illustrated by the magnesite deposits and the mineral springs of that section.

    "Taking the three counties together, one might say that the geology is complex, the solution of which will take considerable time and much patience to decipher."

    Building Materials (in Humboldt County)

    "Brick and Tile. There are only two companies in Humboldt County who manufacture brick or tile and they are able to supply the local and county demand. The Fortuna brickyard at Fortuna formerly owned by J. A. Thompson has been closed down and Mr. Thompson is now interested in the Eureka Brick and Tile Company of Eureka...."

    Quarries (in Humboldt County)

    "The only quarries in the county are those being operated for the purpose of obtaining rock to be used in building the jetty at the mouth of Humboldt harbor and for road metal."

    Limestone (in Humboldt County)

    "There is considerable limestone in the county suitable for burning for lime and also for fertilizer and smelter flux. The most accessible deposits to Humboldt Bay are on Jacoby Creek in Secs. 13 and 14, T. 5 N., R. 1 E., on the property of the Bayside Lumber Company. It is 3 miles from the bay and on the railroad. There is also another deposit on Jacoby Creek owned by J. A. Moore of Blue Lakes, Humboldt County...."

    "There is a large dike of limestone crossing in a northwesterly direction from Trinity County to Humboldt County in T. 4 N., R. 5 E., which extends northwesterly and passes to the east of Horse Mountain and cuts across Willow Creek. This limestone formation has not been developed and is a source of immense quantities of good limestone.

    "There is also considerable limestone in the southeastern section of the county which has not been developed."

  • Humboldt County Mineral Industry (circa 1919) - Excerpt from California Mineral Production for 1919, Bulletin No. 88, by Walter W. Bradley, California State Mining Bureau, 1920, pp. 147-148.

    Area: 3,634 square miles.
    Population: 37,857 (1920 census)
    Location: Northwestern portion of state, bordering on Pacific Ocean.

    "Humboldt County is almost entirely mountainous, transportation within its limits being very largely by wagon road and trail, and until recent years was reached from the outside world by steamer only. The county is rich in mineral resources, among which are brick, chromite, coal, clay, copper, gold, iron, mineral water, natural gas, petroleum, platinum, silver and miscellaneous stone.

    "Six mineral substances as shown by the table given below, having a total value of $43,667, were produced in 1919, as compared with the 1918 output, worth $141,954, the decrease being due to manganese and chromite. Humboldt ranks forty-seventh among the counties of the state for the year.

    "Commercial production for 1919 was as follows:"

    (Headings for the information below are: Substance, Amount, and Value.)

    Brick and clay, ---, $9,271
    Gold, ---, $8,000 (estimated)
    Silver, ---, $50 (estimated)
    Stone, miscellaneous, ---, $25,198
    Other minerals,* ---, $1,148
    (Total value) $43,667

    (* Includes mineral water and natural gas.)

    Humboldt County, 1916 Map, from California Mineral Production for 1919 (with County Maps), Bulletin No. 88, by Walter W. Bradley, California State Mining Bureau, San Francisco: California State Printing Office, 1920, pp. 183. Humboldt County, 1916 Map, from California Mineral Production for 1919
  • Humboldt County Limestone Industry and Deposits (through 1947) - Excerpts from "Limestone in California," by Clarence A. Logan, California Journal of Mines and Geology, Vol. 43, No. 3, July 1947, California Division of Mines, San Francisco, California, pp. 175-357. (Used with permission, California Department of Conservation, California Geological Survey.)

    "Franciscan rocks are known to extend northwest across Humboldt County and are flanked by younger formations on both sides, but the geology has not been mapped in detail. Gold from beach placers and from placer mines in the Klamath River drainage in the northeastern corner of the county, and miscellaneous stone, have been the principal mineral products. Much of the county is rough and timber-covered. Production of redwood lumber and diversified farming have been the most important industries.

    "There are numerous relatively small deposits of limestone, and there was a limited production for local use in early days, but no recorded output has been shown since the compilation of statistics began in 1880, although there has been some production for agricultural use. Larger deposits on which no development has been reported, occur in the eastern and southeastern parts of the county. The Northwestern Pacific Railroad enters the southeast corner of this county, following the canyon of Eel River and is the only rail outlet. The town of Eureka has steamer service.

    "The population of the county was less than 50,000 according to the 1940 census. Eureka, the county seat, with more than one third of the population of the county, is the principal city of northwestern California. The limestone resources are ample for any local requirement likely to arise, but at present there is no operating lime kiln in the coast counties north of San Francisco Bay. As rainfall is rather heavy in the western part of the county and dairying is an important industry there should eventually be a local demand for limestone on the land where alfalfa and such crops are grown...."

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