USA > California > History of California, Volume V > Part 2
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The Coast range province, too, showed this same phenomenon in its Paleozoic and early Mesozoic sediments, but from the bottom of the Cretaceous to the middle of the Miocene conditions were more uniform, indicating moderately quiet advance and retreat of the sea, with minor unconformities, smaller
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HISTORY OF CALIFORNIA
masses of igneous intrusives, and outpourings of surface lavas. The Coast range revolution, about the middle of the Miocene epoch, broke the monotony of this history, and for a time there was much mountain- making activity. Minor outpourings of lava occurred along the coast, while farther to the northeast the Columbian lava flood overwhelmed an area of about two hundred thousand square miles, and the rejuvenation of the Sierra Nevada was beginning.
The Cretaceous section of the Coast ranges is more complete than that of any other single province in America. It lacks only the uppermost portion, and shows a variety of conditions not seen anywhere else, from the boreal faunas of the Knoxville to the tropical faunas of the Horsetown and Chico epochs, with fossil floras interbedded in every formation.
The Tertiary marine section of the Coast ranges is not only the most complete in America, but also more complete than that of any other single geographic region in the world. Every minor division is fully represented by marine faunas, and most of them have freshwater beds intercalated, with fossil plants and freshwater animals.
The Quaternary marine section of the Coast ranges is the most complete that has been described, for this is almost the only known region where there has been much post-Quaternary orogenic activity. In nearly all other regions the Quaternary sediments are still buried under the oceans in which they were deposited.
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OUTLINE OF GEOLOGY
ROCK-FORMING AGENCIES OF CALIFORNIA
Igneous Rocks. A large part of the surface of the state, a little less than one-half, is made up of igneous rocks. Of these the most important group consists of deep-seated granitic rocks, granites, grano-diorites, diorites, and gabbros, compounds of feldspars and ferro-magnesian minerals, such as hornblendes, pyrox- enes, and mica. The greatest of these batholiths is the great igneous mass of the Sierra Nevada, making up the bulk of that mountain chain. Smaller batho- liths of similar character are in the Sierra Madre range, the White Mountain range, the Klamath mountains, and in the Santa Lucia mountains.
Associated with the deep-seated granitic rocks in nearly all these regions there are numerous dyke-rocks, similar in chemical nature to the parent masses, but showing only a small surface area.
A second group is composed of basic intrusives, chiefly peridotites, now largely changed to serpentine, rich in olivine and other ferro-magnesian minerals. These cover great stretches in the Coast ranges, where they are largely of Franciscan age, older than the Cretaceous; they also form less extensive masses in the Sierra Nevada.
A third group is composed of dark lavas, mostly andesites and basalts, surface flows from volcanoes. These are chiefly of Tertiary age, Miocene, and, to- gether with the less important rhyolite lava flows, they cover broad areas in northeastern California, and smaller patches in all the other mountain regions of the state. The flows in northeastern California
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HISTORY OF CALIFORNIA
are a part of the Columbian field, and probably came from fissure-eruptions. The others came from ordinary volcanoes, though in most cases the volcanic cones are long since destroyed. Mt. Shasta and Lassen Peak are the two grandest volcanoes of the state, the southern extension of the Cascade range, still preserving their ancient form and some feeble remnants of their old- time activity.
Inorganic Sediments. The greater part of the surface of California, a little more than half, is made up of sediments. These are of two groups, (I) inorganic, and (2) organic.
The inorganic sediments are far greater in thickness and areal extent, sandstones and shales, derived from the decay of crystalline rocks. The quartz and undecomposed feldspars furnished the sand grains, and the decomposed feldspars furnished the clay for the shales. The sandstones of California are remark- able for the large quantity they contain of undecom- posed fragments of minerals derived from the igneous rocks, so that they are more often arkose and grey- wacke than true sandstones.
Thick beds of aluminous shales, now largely changed to slates, are found in the Carboniferous and Jurassic rocks of the Sierra Nevada, and to a less extent in the Franciscan formation of the Coast ranges. The Auriferous slates also form the surface rocks of considerable areas in the Klamath mountains.
Less altered shales are extensively developed in all the later formations of the state, from the Lower Cretaceous upward, although not on such a grand scale as in the older periods.
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OUTLINE OF GEOLOGY
The greatest individual mass of sediments in Cali- fornia is formed by the Quaternary and Pliocene fluviatile deposits of the Great valley. This mass is about four hundred miles long by fifty in width, and is several thousand feet thick in the middle, thinning out toward the edges, surpassing the enormous mass of Tertiary sediments. These valley deposits have been bored to a depth of three thousand feet, without reaching bed-rock, but there are too few deep borings for an estimate of the average thickness to be possible.
A second great mass of clastic sediments is seen in the Tertiary sandstones of the Coast ranges which extend nearly the entire length of the state, and have a total thickness of about fifteen thousand feet, al- though not all of this at any one place. A remnant of this series is seen along the western flank of the Sierra Nevada in the marine and brackish-water Ione forma- tion, and the upland equivalent is seen in the Auriferous gravels.
A third great mass of sandstones is found in the Cretaceous of the Coast ranges, where a thickness of about thirty thousand feet was deposited. This thickness surpasses by far that of the Tertiary sand- stones, but the areal extent is much less. These, too, overlapped on the foot of the Sierra Nevada.
Smaller masses of sandstone, now largely changed to quartzite, are seen in the early Mesozoic and Paleozoic formations of the Sierra Nevada and Coast ranges, but nowhere forming extensive surface areas.
On the western flank of the Sierra Nevada, through- out the gold belt, there are in the late Paleozoic and in the late Jurassic thick beds of tuffs, or volcanic ash,
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HISTORY OF CALIFORNIA
now altered to greenstone schists. These in places have a thickness of several thousand feet, but do not form considerable areas of the surface rocks.
Organic Sediments. These do not make much of a figure on the areal map of the state, but play a large part in its economic history. They are limestones, siliceous shales, and plant accumulations in the form of coal or lignite.
The limestones are entirely of organic origin, with the exception of some smaller occurrences of late spring deposits, or calcareous tuff, which, however, are large enough to be used in the manufacture of cement.
The great masses of limestones are confined to the Paleozoic and early Mesozoic, though as late as the middle of the Jurassic period there are some large beds of limestone. They are formed of ground up shells, corals, and foraminifers that lived in quiet, clear waters, but are now largely crystalline, most of the evidence of their organic origin having been de- stroyed in the great mountain-making revolutions that have passed over them. The formation of limestone on a large scale in California was confined to epochs that we know from other evidence were warm, and also to epochs when sheltered, clear seas covered portions of the state. In such seas corals and foraminifers abounded, and the evidence of their rock-forming activity is still visible in the coral reefs of the Paleozoic and Triassic, and the Fusulina limestone of the Carboniferous.
From the middle of the Mesozoic up to the Eocene it was still warm enough at times for reef-building
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OUTLINE OF GEOLOGY
corals, and foraminifers to have flourished in the seas of California; but the warm epoch of the Middle Jurassic was a time of igneous activity, and during the Cretaceous there was too much sand and mud poured into the water for these organisms to find a favorable habitat.
Limestones, at least in part formed by corals, have a thickness of several thousand feet in the Cambrian of Inyo county, but the areal extent is unknown. The Devonian of Shasta and Siskiyou counties shows coral reef rock to the thickness of several hundreds of feet, of small area. These are all surpassed in the great masses of Carboniferous limestone, of the White mountains, the western flank of the Sierra Nevada, and the Klamath mountains, where the lenticular beds sometimes attain a thickness of two thousand feet.
The Santa Lucia limestone, in the Coast ranges, of doubtful Paleozoic age, also occur in large beds, amounting to several hundred feet in thickness, now changed to marble.
The Upper Triassic of Shasta and Plumas counties has lenses of limestone in places four or five hundred feet thick, forming important topographic features, and largely formed by the agency of corals.
The Franciscan series of the Coast ranges has similar limestone masses of lenticular form, amounting in places to a few hundred feet in thickness, and wholly destitute of fossils, except a few traces of foraminifers.
The Cretaceous lacks limestone beds, except a local accumulation of shell limestone in the Knoxville formation of Colusa county, where a thickness of only a few feet is developed.
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HISTORY OF CALIFORNIA
The Eocene of the Santa Cruz mountains has some thin beds of limestone, and the Miocene of Santa Barbara, San Luis Obispo, and Orange counties has shell limestone amounting to as much as fifty feet in thickness. With the exception of these local occur- rences there are no limestone masses in the marine beds of California from the middle of the Jurassic to the Quaternary, the Jurassic and Knoxville being characterized by thick beds of shale, and the other formations, from the Horsetown up, by enormous beds of sandstone.
Siliceous Organic Sediments. Among the most remarkable features of the stratigraphy of California are the thick beds of siliceous organic sediments. In the Monterey shale of the middle Tertiary in the Coast ranges such sediments are extensivey developed, and in places reach a thickness of five thousand feet. These are not shales in the ordinary sense, for they are chiefly organic in origin, the remains of microscopic diatoms and radiolaria. Similar deposits are known also in the Eocene of the middle Coast ranges, but on a smaller scale. These organic siliceous shales are of great economic importance, for they have furnished nearly all of the petroleum of California.
Similar masses of siliceous organic sediments are known in the Coast ranges in the Franciscan forma- tion, of the earlier Mesozoic, but they are no longer shales, rather hard, flinty rocks, with the organic matter long since removed, and the fossil tests of radiolaria almost entirely destroyed, so that the rocks now show little resemblance to organic sediments.
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OUTLINE OF GEOLOGY
In the Mother Lode region of the Sierra Nevada there are somewhat similar chert masses, in beds sup- posed to be Jurassic in age. These too are probably of radiolarian origin. In the Middle Triassic of Shasta county a series of siliceous shales almost without sand grains, and about two thousand feet thick, like- wise was probably formed partly from the shells of siliceous organisms.
The Lower Carboniferous and the Devonian of Shasta and Siskiyou counties also contain many hundreds of feet of fine-grained so-called siliceous shales that are probably, at least in part, metamorphosed organic sediments. Shells of diatoms and radiolaria are extremely rare in all these older beds, but organic silica is very soluble, and even a slight degree of metamorphism destroys the delicate tests, and thus obliterates the evidence of their origin.
Gold Deposits of California. The gold deposits of California, which have added in the last sixty years considerably more than a billion dollars to the world's wealth, lie principally in the gold belt of the Sierra Nevada. They are of two sorts, vein or lode deposits, and Auriferous gravels. The lode deposits are in quartz veins in the metamorphic auriferous slates and associated igneous rocks; they are deep seated chemical deposits formed by the hot waters that permeated these rocks in the periods of mountain making activity and great intrusions of granitic masses in the time preceding the Cretaceous age. They still continue and will continue for many years to be a great source of wealth to our state.
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HISTORY OF CALIFORNIA
The Auriferous gravels are sedimentary deposits laid down by the ancient Tertiary rivers that won their golden freight from the wear and tear of the gold quartz veins of the old mountain highland during the long period of erosion that lasted throughout the end of the Cretaceous and early part of the Tertiary periods. The accumulation is still going in the modern bars of streams in the gold belt, though not on such a grand scale as in the Tertiary rivers.
Coal Deposits. During the Eocene epoch plant remains accumulated to a considerable extent in the swamps of the old embayment of California, especially along the western flank of the Sierra Nevada near Ione, the Coast range island area of the Mt. Diablo region, and in the middle Coast ranges of Monterey, San Benito, and Fresno counties. These leaf beds have since been compacted into lignite, and in a few places into true coal.
Chemical Deposits. In Kern, San Bernardino, San Diego, and Inyo counties there are extensive chemical precipitates of salt, soda, potash, borax, and gypsum, concentrates from the old lakes and salt pans of the arid region, from Tertiary up to the present. The areal extent is not large, but they are scattered over enormous stretches of country, and are of great present or prospective economic importance. Outranking all the other chemical deposits in abundance and impor- tance the petroleum of California, distilled by natural processes from the organic siliceous shales of the Tertiary, has come to the front, and in recent years has surpassed gold as the most characteristic product of the "Golden State."
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OUTLINE OF GEOLOGY
Most Important Events in the Geologic History of California. In early Cambrian time sedimentation began in the eastern part of California on the western shores of the Great Basin sea, and kept up, almost without interruption, until the middle of the Jurassic. During this long period the greater part of the state appears to have been above water, although during the Santa Lucia epoch (Paleozoic?) calcareous sediments were laid down in the Coast ranges, and during the Carboniferous the Great Basin sea spread westward and southward over much of the region of the Sierra Nevada. In the Permo-Carboniferous, California, al- though remote from the center of activity, felt the effects of the Appalachian revolution, for an uplift began along the axis of the Sierra Nevada, manifesting itself in great outpourings of volcanic tuffs, which now are preserved as greenstones, showing by their marine fossils that they were deposited in the sea. Further west, the calcareous sediments of the Santa Lucia mountains were raised above the sea and changed into marbles and schists.
The Appalachian revolution restricted, but did not obliterate, the Great Basin sea, nor did it confine the relentless advance of the Pacific ocean, for during the Jurassic marine sediments were laid down along the Coast ranges, and along the sides of the Sierra. The Franciscan series has preserved this record in the Coast ranges, and the Mariposa formation in eastern California.
The Cordilleran revolution began in the Great Basin sea in the middle of the Jurassic, when that body of water, after many vicissitudes, finally went dry, and
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HISTORY OF CALIFORNIA
has never since been covered by salt water, although in later ages Tertiary and Quaternary lakes have been scattered over its dead basin.
This elevation culminated, in late Jurassic time, in the upturning, and metamorphism of the Triassic and Jurassic sediments of the Sierra Nevada, and the Franciscan beds of the Coast ranges. Since that time the Sierra Nevada has been above the sea, subjected to continuous erosion, and there we see the deeper results of metamorphism. The Coast ranges, on the other hand, have been buried under the later Cretaceous and Tertiary sediments, and the deeper products of meta- morphism are little exposed. The crystalline schists of the Coast ranges are evidences of rather shallow hydrothermal metamorphism, while the great masses of thoroughly altered rocks and auriferous veins of the Sierra Nevada show the deep-seated action in that region. This explains the fundamental difference be- tween the metamorphic rocks of the two areas, where the phenomenon was contemporaneous, and the rocks affected were similar in the beginning.
During this epoch along the west coast, from Oregon to Lower California, there was much igneous activity, and great masses of serpentine are now seen throughout the Coast ranges, the results of alteration of the peridotite dykes that were intruded into the Franciscan sediments.
It is probable, also, that the Cordilleran revolution was something more than a mere orogenic disturbance, for it marks a change from the warmth of the Middle Jurassic, with its cycads and reef-building corals, to the cooler epoch of the Upper Jurassic, with its scanty
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OUTLINE OF GEOLOGY
boreal fauna. The Middle Jurassic was of tropical type, from Mexico to Alaska, and uniform up to Franz Joseph Land. The Upper Jurassic, on the other hand, was of Boreal type from the Arctic region down as far as California, and for a short epoch in the Portland these conditions extended down as far as Mexico.
After this mountain-making epoch near the close of the Jurassic, the sea again encroached on the up- lifted area, and the Knoxville sediments were laid down on the western border of the Coast ranges. The lower Knoxville beds contain a fauna closely related to that of the Mariposa, still with Jurassic types of Aucella, and with the same poverty of other animals. But the upper Knoxville beds, while still retaining reminiscenses of the Boreal region in Aucella and a few other forms, show a preponderance of life characteristic of more favorable conditions. Aucellas of northerly habit mingle with cephalopods that did not belong in the Boreal region, and on the nearby land cycads abounded.
With the opening of the Horsetown epoch, the revolution of faunas and floras was complete, the cli- mate had become tropical, and swarms of Trigonia, Nautilus and Ammonites like those of India and eastern Africa occupied the shallow seas of northern Cali- fornia. These beds were deposited only in a narrow strip from Shasta county down to the neighborhood of Mt. Diablo, the rest of the state being above water.
While the Paleozoic and the earlier part of the Mesozoic were characterized by the formation of immense masses of limestone, and the Jurassic and the Knoxville by the deposition of thick beds of
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HISTORY OF CALIFORNIA
shale, the middle Cretaceous inaugurated a sandstone- forming era, which lasted through the entire Tertiary.
During the Upper Cretaceous Chico epoch the climatic conditions and faunal geography remained unchanged, but the sea encroached still further on the land, reaching the foot of the Sierra Nevada, where, in Butte county, the unaltered and slightly tilted sandstones of the Upper Cretaceous may be seen resting upon the upturned, metamorphosed and eroded rocks of the backbone of California.
By the end of Cretaceous time the subsidence and erosion of the western part of the continent had almost established a connection between the Pacific Gulf in California and Oregon with the old Mediterranean sea of the Mississippi valley. The intervening isthmus not covered by salt water was worn down to base-level and wide expanses of flats were covered with marshes, which eventually formed coal, preserving a very similar flora from the outliers of the Mississippi valley almost to the Pacific coast. These coal-forming conditions reached far up into Alaska, where almost under the Arctic circle types of plants flourished that, to-day, could not live in the open north of Mexico.
In Eocene time the climatic and geographic con- ditions remained the same as in the Upper Cretaceous, but the sea had encroached still further on the land, and the base-levelling of the backbone of the continent was more complete. The aged rivers began to deposit their loads of sediments, beginning the formation of the Auriferous gravels, the first great source of wealth of the Pacific coast.
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OUTLINE OF GEOLOGY
Tropical conditions still prevailed up as far as Alaska, and coal was still formed abundantly where vegetation is now scanty. If a geologist in western America had first named the geologic systems, the Eocene would have received the name "Carboniferous," for most of the coal on the west coast belongs to that epoch. During the Eocene, also, a temporary connection was established between the Pacific and the Atlantic basins, for in California and Oregon the Atlantic "fingerpost of the Eocene," Venericardia planicosta is found along with Pacific types.
Before the Miocene epoch this Atlantic connection had ceased, and the faunas of the later Tertiary were wholly of the Pacific type. The lower Miocene was still warm, for we find in its fauna a Nautilus still persisting, and other genera now found only in southern waters. Quiet accumulation of sediments with abun- dant organic remains, diatoms and radiolaria, was going on in the Coast range region. From these the petroleum, which has added so much to the wealth of California, was afterwards distilled, in the great disturbance that took place after the close of the Monterey epoch of the Miocene.
The vast outpouring of the Columbian lava flow, which covered an area of more than two hundred thousand square miles, including the northeastern part of California, occurred about the middle of the Miocene, and the Coast range disturbance was probably a local phase of the same revolution.
In the upper Miocene the climate was no longer subtropical, but warm-temperate and moist, like that of the states bordering the present Gulf of Mexico.
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HISTORY OF CALIFORNIA
Marine animals like those of our time abounded in the waters, but along with them were some southern forms. And on the land elms, walnuts, hickories and laurels flourished, indicating a temperate, rainy climate, moister if not milder than that of today in the same region.
In the Sierra Nevada in this epoch there were large rivers, not running swiftly in deep cañons, as they do now, but winding slowly down low grades, overloaded with sediments, the Auriferous gravels. These dead rivers, which must have run on a low plain not far above sea-level, are now found high up in the Sierra Nevada, with their channels buried deeply under later lava flows, and warped by later orogenic movements.
In the Pliocene the warm-temperate types of plants have disappeared temporarily, and the salt-water faunas, too, show a change for the worse. The fresh- water Pliocene lake beds also show the influence of a cooler climate, for while many of the fossil mollusca are the same as species now existing in that region, others that are still living are now found only in the Klamath mountains.
Now the land had begun to encroach on the sea, and the shore was receding westward. The whole west coast was rising, and the salt waters no longer reached to the foot of the Sierra Nevada, nor even to the great valley. But the elevation was not uniform, for valleys in the Coast ranges that had been cut during the Miocene were filled with sediments during the Pliocene, which was made possible by local subsidence along the coast. The immense deposits of the great valley belong partly to this epoch, and partly to the
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OUTLINE OF GEOLOGY
Quaternary, but they are wholly of fluviatile origin. These gravels and silts have been bored into to the depth of three thousand feet in the middle of the great valley, and still bed-rock was not reached.
During the Pliocene the Sierra Nevada was elevated again, and the rejuvenation of the streams carried the sediments out of the mountains to the flats of the valley floor, piling up the gravels and clays now known as the Tulare formation. California of that time was very much like California of today, with a great mountain range on the east; in the middle a long, broad valley, low-lying, and covered in many places by fresh- water lakes; and on the west, a long, low narrow mountain range. On the submerged narrow coastal plain, and in troughs parallel to this range, were laid down the marine Pliocene sediments.
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