USA > California > San Luis Obispo County > History of San Luis Obispo County, California, with illustrations and biographical sketches of its prominent men and pioneers > Part 60
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California, under similar conditions, i. e., whenever there is an opening in the littoral chain to allow the shore winds access into the interior, the inward current being produced by the ascent of the over-heated air of the plain, leaving a partial vacuum, which the sea breeze rushes in to fill. In such places a land breeze prevails at night. The influx of such cold winds, charged with moisture, lessens the mean temperature of the summer of these plains, while at the same time it adds very con- siderably to the fertility of the soil, which at times would be almost reduced to barrenness from the drought. In several places on the middle terrace the soil was cracked in fissures a foot wide, some yards long, and three or four feet in depth, the result of the excessive summer heat on a plastic clay.
The Gavilan Range of hills forms the eastern boundary of this valley. This range at its northern part is essen- tially granitic, flanked on its lowest side by metamor- phic limestone (crystalline carbonate in places), 300 to 400 feet in thickness; lower down, the foot-hills are made up of a series of soft sandstone, which extend in an almost straight line from the mouth of the Pajaro to the Mission San Miguel, a distance of eighty or ninety miles.
These sedimentary beds dip towards the valley, as in a southwest direction, and form the true bottom of the valley, having been reached at the depth of forty feet in sinking a well near Mr. Hills. These sandstones also form the low hills upon the west side of the valley, where they constitute the base of the wide mountain ridge, here one of the coast ranges. This ridge, which com- mences at Point Pinos, the south point of Monterey, runs in a southeast direction, and approaches the Salinas River fifty-five miles from its mouth, has a central axis of feld- spathic granite, coarse-grained, and of a bluish tint on a fresh fracture, owing to the presence of adularia. This rock, which occupies only a few miles of the surface at the shore of the bay, as the mountain rises to a greater elevation farther south, also covers a greater width and forms the highest summits of the range which exceeds 3,500 feet; as it passes south it becomes more hornblen- dic and magnesian in its character. East of the granitic axis a mass of slaty, serpentine, and trappean rock is pro- truded, forming a second ridge running a parallel course, whose altitude does not reach that of the granitic chain, but which, from its proximity to the plain, hides from the latter the granitic hills, and presents to view its sharp and angular crests. As this igneous rock runs south it sends spurs out into the valley, which, upheaving the later formed strata, narrow the plain so as to reduce it to two or three miles broad, ten miles north of Mission San Mig- uel, and south of that to lessen it merely to the condition of the river bed without a lateral plain.
The sandstone and overlying beds have been both partially elevated and cut through by these serpentine and trappean rocks; in places the sandstone is hard, rings to the hammer, and has a slaty appearance. A few miles north of the Mission San Miguel, trappean dykes cross the road, cutting the sandstone at an oblique angle to the line of strike. In the upper beds the calcareous strata are separated by a quartzose bed, four to ten feet thick, which presents the appearance of agate and opales- cent quartz veins, one to two inches thick, and separated a few feet from each other; three and sometimes four of these veins occur in the sandy bed; these silicious veins are in places accompanied by serpentine and talcose clays which tinge the edges of the veins green; when any portion of this vein stone is removed, it is found to be intersected by lines of former fracture cemented anew, giving a pretty agate appearance to the various tints of the quartz lines. These veins mostly correspond to the plain of deposition of the strata in which they are included; in a few instan-
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ces they have been seen cutting the strata through at a slight angle. The presence of these veins serve, from their hardness and readiness to recognize them, as a good mark to determine the presence of the upper fossiliferous beds. In themselves they are the evidences of the exist- ence of thermal waters highly charged with soluble silica traversing fissures in the strata and insinuating the fluid between the laminæ of deposition. These layers were first observed in leaving the Salinas and ascending the hills in which the San Antonio River heads. Here a better view of the constitution of the Point Pinos Chain was had than elsewhere below, when, on account of the width of the plain, the road lay along the river side away from the mountains.
South of the Mission Soledad, which lies thirty-five miles up the valley, the mountains converge considerably, and the low foot-hills spread into and narrow the plain. The diluvial clays are deep, often more than forty feet exposed. The yellow sandstone which, from Hills ranch for thirty miles southward, is observed to rise up from the valley with a gentle slope, now disappears, and a whitish ar- gillo-calcareous rock takes its place; it is probably an upper stratum of the series brought to light by the lesser slope. The paste of the rock is soft, friable and easily worn down by the elements; of a slightly green tint, cal- careous, and very full of casts of dosinia, venus, natica, etc. (vide Mr. Conrad's report), many of which were very imperfect; a few pecten impressions were intermingled; small masses of this rock were scattered over the terrace and the plain beneath. The observed thickness of this bed was about fifty feet, its whole depth not being exposed. On crossing the divort* between the small stream, a trib- utary of the Salinas, and the waters of the San Antonio, this bed was found to occupy a large surface and to be the uppermost rock. Its dip, when first observed, was to the southwest, so that it lay on the west or Pacific slope of the Point Pinos Chain, which is here a series of low and broad hills.
Underneath this whitish clay rock lies a bed of con- glomerate, made up of a clay paste cementing rounded and broken pebbles of prase, hyalitic jaspery quartz, obsidian and serpentine. The observed thickness of this conglomerate was eighty feet. It contains no fossils. Below the conglomerate a reddish sandstone grit was ob- seved. This grit is one of the beds which repose on the east side of the range, and dip under the Salinas River, and rises up again on the sides of the Gavilan Range. This constitutes the whole section of stratified rocks.
The axial rocks did not appear exposed, but the ar- royos brought down, beside serpentine, obsidian, and trap, broken angular fragments of gneissose rock and feld- spathic granite, so that a section of these hills would af- ford the following details :-
Igneous rock .- Granite, gneiss, serpentine, obsidian, trap, in veins.
Sedimentary rock .- From below upward; Reddish sandstone grit; conglomerate green, quartzose; whitish green calcareous and fossiliferous beds, in brown sand- stone, with dosinia and pecten. The whitish green cal- careous rock is met the entire length of the chain for thirty miles, terminating a few miles south of Mission San Miguel, where they can be traced passing up the Estrella River, and forming the side hills of the river bottom upon which the terraces are placed.
The fossils found in the sandstones on the west side were Dosinia Monteregana, Dosinia Montana, Dosinia Subobliqua, Dosinia Longula (vide Mr. Conrad's re-
port) which extended from the Salinas River, at Mr. Hill's at the north extremity of the valley, to near the Mission San Miguel, at the south end. Ten miles south of the junction of the Estrella and Salinas Rivers the valley of the Salinas may be said to terminate. The granitic rocks and sandstones of the Point Pinos Chain cross the river and form the eastern boundary of that stream for some miles further south.
The granitic rocks at this point are low hills, flanked by the sandstones, having a slight dip to the southwest. By following the course of the river, which here comes from the S. S. E. a small valley is reached, the valley of the Mis- sion Santa Margarita.
The geological structure of this valley was obtained very imperfectly, partly on account of its great size and the rapid transit over it, but chiefly on account of the fogs, which for some days so completely hid the plain as to render everything farther off than fifty yards wholly undiscernible. Fossils similar to those found on San Antonio hill slopes were found in the bed of the . river near Mr. Hill's ranch; so that this upper layer of the sandstones of the Point Pinos Range extends the whole length of the valley on its west side. They are, however, inferior to the beds containing the stres and echinoderms of Santa Margarita Valley.
SANTA MARGARITA VALLEY.
The valley of Santa Margarita, in San Luis Obispo County, comprises the sources of the Salinas River. It is a small plain, whose greatest breadth is nine miles, nar- rowed toward its southern end to a width of three miles by upheaval of low hills; it lies between the valley of San Luis Obispo on the west and the valley of the Estrella or San Juan River on the east, and may be looked upon as the southern prolongation of the Salinas Valley, from which it is separated by the low hills south of San Mig- uel. Its eastern boundary is the prolongation of the Point Pinos Range of hills, which have been described as running southeast from Monterey, and which, fifty miles south of that city, become less elevated and more spread out; in this southerly course they cross the Salinas River, and in its upper portion become the eastern boundary, as they were its western lower down; along this valley they are low mountains not more than 1,000 to 1,200 feet above the level of the plain, itself, 950 feet above the sea; further south these hills rise to a considerable height, are more pronounced, and known then as the San José Mountains. The western boundary of the plain is another of the coast ranges, the Santa Lucia Hills, one of the longest and most decided of the coast ranges, with few breaks or passes, and rising to a height of 2,500 feet. The valley between these limits is one of the most beautiful and fer- tile in south California, possessing fine grass, with abun- dance of running streams in the bottom, the side hills clothed with live-oaks and cotton-wood and covered with a luxuriant crop of wild oats (avena fatua) which was nat- urally preserved, and at the time of visit (January) served as food for the multitude of deer and horned cattle, which found abundant sustenance here. The oak trees are covered, as to their branches, with the beautiful ram- alina, which, hanging gracefully in festoons, with its light green tint, convey the idea of spring at a season when vegetable growth is nearly suspended. The Salinas River flows upon the east side of this valley, from the level plain of which it is separated by a range of low hills of sand- stone grit; beyond (east of) the river, the granitic axis of this range appears, having the same mineral constitution as further north, largely feldspathic, with well-defined or- those crystals, of a light flesh color, vitreous quartz, and small plates of diallage, whose green tint a Ids a lively con- trast to the feldspar, and gives an appearance of syenite to the whole mass; the rock is cut through by thin green
*"Divort"-This word expresses fully what no other word at present in use does. The word "divide" is not etymologically applicable, as it does not convey the idea of altitude as the cause of separation; while the word divort implies elevation, the cause of the "divortia aquarum" whence its derivation also. It is hoped that this expression will meet with favor and application .- P. R. R. Sur- vey.
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HISTORY OF SAN LUIS OBISPO COUNTY.
threads of oxide of chrome, along the line of which the mass breaks into small rhombic fragments. It is a gran- ite which decays readily from the separation of the feld- spar crystal, which drops out by the weathering of the paste.
At the southern end of this valley the granite becomes highly magnesian from the intermixture of serpentine protrusion. These are derived from the Santa Lucia, whose axis is serpentine and trappean rock, spurs of which are given off and enter the plain at various points. One of these protrusions occurs in the center of the valley, within one and a half miles of the entrance of the pass to San Luis Valley; it is a mass of augitic trap, which rises up from the plain in knobs ten to fifteen feet high, increasing in height to the south, where it is found elevating the brown sandstone from one hundred to five hundred feet high, and forming central bosses from fifty to one hun- dred feet on the summit. These hills are covered with wild oats and oak, and produce the finest pasture in the valley; as they increase in height they merge into the main mass of the Santa Lucia. To the northwest the trap vein can be traced along the valley several miles, until it passes into the same range west of the old mission, Santa Margarita (Don Joachin de Estrada's residence).
The old mission establishment stands on a terrace raised about sixteen feet above the plain, on its western side; at the base of the terrace lies one of the forks of the Salinas, which heads up in the Santa Lucia Range a few miles southwest; the terrace is not more than one-fourth of a mile wide, and stretches northwest for one and a half miles; where the river cuts its margin it exposes here and there sandstone and argillite beds similar to those of the San Antonio River, cut up and altered by intrusion of trap rock, steatitic and talcose clays, and shales, which have flexed and contorted the strata in various directions. This intruded rock can be traced several miles, both north and south, preserving a direction of north 60° west, south 60° east.
The valley is closed at its south extremity by an eleva- tion of the sandstone, caused by the intrusion of a mass of serpentine with augite, which runs in an easterly direc- tion toward the Toro Hills, small masses of granite, out- liers of the San José Mountains, and forms a natural di- vision between the Santa Margarita and San José Valleys.
On account of the frequent and extensive intrusions of augite and serpentine in this valley, it is difficult, in many places, to say what is the original dip of the strata; thus, in the north, the white fossiliferous beds dip to the southwest, conforming to the dip of the strata of the San Antonio River, and there on the west flank of the Point Pinos Range, while in the south of the valley the same strata dip eastward. Observation had, however, shown that as an elevating agent the Point Pinos (or San José) Mountain Range extended its influence to a much greater extent laterally than the Santa Lucia Mountains, and that where the strata reposes without any subsequent altera- tion or flexion they are found to be conformable to the Point Pinos granitic axis.
The sedimentary bed lowest in position in this valley, is the same as that observed at San Antonio, a breccia conglomerate of quartz ore, and jaspery pebbles, in an aluminous paste, the whole having a light brownish green color. This was not occupying a prominent posi- tion, but was found cropping out near the river beyond the low hills on the east side of the plain. Above this is a fine-grained sandstone, greyish white in color, fri- able, and weathering readily into holes, intersected with threads of sulphate of lime, which traverse the rock in horizontal lines, having a direction north twenty degrees west; the gypsum was in places granular and compact; in others, crystalline; the seams one-half to an inch thick, and stained green with carbonate of copper (mal-
achite). This appearance was presented wherever au- gitic rock cut through the elevated sandstone, and was well displayed at the Rinconada Hills. The gypsum, being readily removed by the weathering of the rock, is dissolved by the waters, and finds its way into the Salinas, to which it imparts its flavor and unhealthy action, and from which being present the river has derived its name.
Besides the gypsum veins, another set of threads cross the foregoing at an oblique angle; these are filled with limonite (peroxide of iron). These two classes of veins render the sandstone readily recognizable wherever found. The thickness of this bed in the valley was 250 feet. In Panza Valley, lying several miles to the east, and on the other slope of the granite axis, it was found much thicker. No fossils were observed in either of these rocks; but it is probable that the upper layers may yet be found fossiliferous.
Above these, and conformable to them, was a whitish sandstone rock, coarse in its lower layers, with pebbles of rounded, white quartz. Calcareous fossiliferous lay- ers occurred in the upper part of this sandstone, which had a dip of thirty-five degrees to the southwest, the strike, north forty-six degrees west. The total thickness of this rock is nearly 450 feet, and may be sub-divided conveniently into four beds, commencing with the most inferior :-
First bed reposes on the agatic or flinty layers, de- scribed as met with at the upper end of the Salinas Val- ley; is about 200 feet thick; a whitish sandstone grit, containing calcareous layers two to four feet thick. These layers are mostly made of ostrea titan (Conrad) in a condition tolerably perfect, cemented by a calcareous paste, the debris of the shells comminuted finely; the paste includes fine grains of rounded quartz pebble. This bed of ostrea was the first one encountered on en- tering the valley where it was found, fifty yards to the left of the wagon road, and less than four miles north of Don Joachin's residence.
Second bed lies above the foregoing, from which it is separated by a quartz grit layer; it is a grey sandstone, including a calcareous cement; it contains a mass of broken shells, forming a cement mass in which are im- bedded layers of ostrea and pecten; the ostrea in this bed have not the size of the mollusc of the first bed. The pectens are large, rarely perfect, and when so, in such a soft condition that it was found difficult to preserve them. The pecten (hinnites crassa, vide Conrad's re- port) as a fossil, more abundant than the oyster. This bed averages from seventy to eighty-five feet in thick- ness.
Third bed varies from sixty to ninety feet thick; is made up almost completely of white calcareous cement, broken shell, and quartz pebble. The fossils lie in two layers, separated by a bed of sand rock. The lower layer contains ostrea and pecten (hinnites) about sixty inches thick; in the upper, ostrea and asterodapsis. The latter (echinoderm) is the characteristic of this bed; it was not found in the lower beds; the individuals vary in size from one-fourth to one and one-half inch across; they are in every respect similar to the Estrella fossils; pecten disdus of a small size was found in this upper bed.
Fourth bed; a soft, brown sandstone, which splits readily into thin slabs, perforated with circular holes, three-fourths inch in diameter, bored obliquely, showing . the action of boring molluscs upon it; thickens from three to six feet.
Accompanying the echinoderms was a mass of broken fragments of their own species; this comminution took place while the bed was yet soft and inhabited, as few of the specimens are broken in places, though so brittle that it is difficult to remove them; they lie crowded to- gether and conformable to the plane of deposition, as
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GEOLOGY.
do also the ostrea and pecten. The ostrea lie in regular layers with their flat shell uppermost, apparently undis- turbed except by the general elevation.
Mr. Conrad has described the pecten as a hinnites, and given the characters of the fossils in his report.
These four beds were never found together in the same immediate locality, but usually within a longitudi- nal range of five miles. The first bed was rarely up- heaved, and constituted the level ground of the valley, while beds two and three were usually found cropping out of the low hills on the east side of the valley; the continuity was, however, satisfactorily traced in several instances.
Some of the beds, as that containing the astero- dapsis (laganum), were brittle so as to render it difficult to preserve the specimens from falling to pieces; while the ostrea layers were sometimes imbedded in so hard a matrix that it was difficult to remove them without fract- ure. Measured by the foot, several of the oyster shells were fourteen inches long by seven inches wide, and few of them were less than six inches long. The thickness of the under shell is remarkable, some of them being five inches in depth.
It is worthy of remark that the beds, although within few yards of each other, had not their fossils intermingled, as it were; thus the asterodapsis, though the most abun- dant shell of the upper bed, was not found in the second lowest ostrea bed-this might more properly be called the hinnites bed-which latter was also unattended by the Janira estrellana, which however, was freely inter- mingled with the laganum; and. lastly, that the layers perforated by the pholadines were only found above the upper bed, and formed loose stones upon the surface, accompanied by rounded pebbles of jasper and quartz.
The height of these hills rarely exceeded 100 feet, more frequently about eighty feet, with rounded sides and summit, and presenting bluff edges to the west. As this was the direction of the dip, which did not anywhere in these beds exceed forty degrees, the strata were un- covered by denudation; indeed, everywhere these hills were examined they were found to have suffered exten- sively by the denuding effects of currents, which, sweep- ing in a meridional direction, removed large masses of this stratum, and converted what was an inclined slope into a series of rounded hills.
The flattened summit of these hillocks with the bored slates tends to show that at the time when these were last covered by water they must have nearly reached the level of the sea of that period. It may be remarked of the sandstone hills of the west side of the valley, that those which are first met with are also flat on their sum- mit, and under 150 feet in altitude.
Below these beds, interesting from their fossil con- tents, and separating them from the gypseous sandstone, lies the white argillaceous rock with the layers of chal- cedonic and opalescent quartz, already spoken of as met with on the San Antonio hills, beds containing dosinia, venus, and natica. In a geological sense, as well as topographical, the argillite is inferior; for it here occu- pies the middle of the valley beside the stream; it dipped northwest from sixty to seventy degrees, and was so hid- den by alluvium as to prevent any exploration of its beds. It has a light yellow tint, becoming in places almost white; granular in texture, and breaking with a splintery fracture. In places the strata were almost ver- tical, not more than fifty feet was exposed.
There white ostrea beds were the most modern rock observed in the valley. Passing westward for a couple of miles, no rock was exposed; and when the Pacific side of the valley was reached, protusions of trap and serpentine presented themselves to view, with the brown sandstones dipping toward the center of the plain.
These are the foot-hills of the Santa Lucia Range, a mountain chain which is described elsewhere in the report.
These sandstones underlie the valley dipping beneath the strata already described, and having a position below the breccia conglomerate of the east of the plain, and lying between it and the granitoid axis. I look upon them as repetitions of the gypseous and saline sandstones found near the base of Panza.
The valley is a true basin; the conglomerate of the last rising up near the summit of Santa Lucia Range; above it the brown and yellow gypseous sandstone; then the San Antonio beds with dosinia; above these, the ostrea and pecten beds-all conformable to each other and to the volcanic rock and the granite, and all having their dip reversed in portions of the valley from local up- heaval.
The whole number of species found in these beds were: Ostrea titan, hinnites crassa, cyclas permacra, balanus estrellanus, pecten discus, asterodapsis antiselli.
Cyclas and hinnites with pecten found in bed two. Balanus was found in bed three, with asterodapsis.
POINT PINOS RANGE AND SIERRA SAN JOSÉ.
This important chain of the Coast Range was first encountered in the center of San Luis Obispo County, where the eastern boundary of the Salinas Valley sepa- rates the upper course of that river from its tributary, the Estrella. The junction of these streams is near the Mission San Miguel; the low hills which form the east- ern boundary of the Salinas Valley at this point are made up of the soft, brownish sandstones which, further north, have been also found lying at the slopes of Ga- vilan, whose upper strata contains the dosinia species, of which four varieties have been enumerated by Mr. Con- rad. In this place these strata slope at a universal angle to the west; and although no primary rock is observed in passing eastward across these hills, yet both north and south of the point the granite rock is considerably upraised. If from the mission a line be drawn in direction southeast, it will accurately cover the range until it is merged in the immense primary upheave called San Emilio Mountain. Projecting a line in a northwest direction, also from the mission, it traverses the trend of a mountain chain which, in its course, gives rise to the waters of San Antonio River, and forms a prominent feature of the Coast Range of Monterey County, and finally terminates in the southwest extremity of Monte- rey Bay at Point Pinos. With the short break alluded to as lying in the Salinas Valley, it is a continuous chain, and might, perhaps, receive a common name. By the title of San Jose Mountains, that portion between the upper waters of the Salinas River and the valley of Panza and Carrisa are known. There, it is a chain ap- proximating 3,000 feet above the sea, and from twelve to sixteen miles in breadth. While we restrict the name of San José to this southern portion, we shall, both topographically and geographically, look upon the whole line from Point Pinos to the head-waters of the Santa Clara and Santa Maria Rivers as one mountain system extending 250 miles from north to south, throughout the whole of which extent it preserves a character remark- ably similar. The northern termination at Monterey Bay displays the usual character of the axial rock, a feldspathic granite, containing only scattered crystals of mica with adularia and epidote, which communicate a green tinge to the mass.
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