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 62
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which are washed and torn by the force of the waves; this character of shore line continuing to Estero Bay on the north, where, owing to the occurrence of the soft uppermost rocks on shore, the sea makes an inroad, which is checked further north by the sharp crest of the Santa Lucia Range, at Punto Gordo. Between this headland and the south border of the Estero Bay the valley of San Luis extends, opening to the northwest, and allowing the winds and moisture to enter and sup- ply it with a much greater rain-fall and heavier dews than are to be found in the valleys east of the range; owing to this, as well as the lesser altitude, the climate is warm, and the vegetation approaches an intertropical character.
The eastern margin of the valley is formed of the sandstone lying against the serpentine axis of the Santa Lucia; these sandstones dip toward the valley and are lost beneath the alluvium.
Along the east side of the valley, lying close to the foot of the sandstones (not more than one mile west), is a series of elevated buttes of serpentine and trappean rock, which can be traced traversing the valley from its northern limit, following the base of the Santa Lucia Range, of a tri- angular form, the serpentine, lying on the west side of the butte, forming its chief mass and determining its crested outline; the eastern slope of the conglomerate rock is at an angle of 45°, serpentine lying underneath it and protruding on the western edge of the buttes.
Further to the south these buttes converge in direc- tion, or nearly so, with the upheaving rock of the low hills along the coast, and both unite in closing the San Luis Valley to the south, forming the elevated land of Nipomo, and thence south till the valley of Guadalupe Largo is reached.
From these buttes the valley is a plain or a gradual slope from four to six miles, when the low hills between it and the coast are encountered; toward these hills the waters roll and find their way partly out by low passes into the ocean, while in some places large ponds and marshes are formed by their collection. The low hills of the coast can be well seen immediately west of the town, whence the river which waters the village of San Luis Obispo finds its way out west of the Corral de Piedras. The first stratum met with is a thick bed of conglomer- ate and grit rock; beds of quartzose pebbles, cemented by a calcareous clay paste, of a greenish yellow color, mostly made up of broken trap rock, a few serpentine and porphyry pebbles are also inclosed, but it is chiefly trappean, and is thus easily distinguished from the green conglomerates of the Santa Margarita Valley. The thickness of this bed is not less than 300 feet, including some intercalated layers of finer grit with white pebble; above this is a yellow sandstone, soft, and easily disin- tegrated; this sandstone is 150 feet in thickness; then occurs the asphalt rock, a greenish yellow bed, where not highly charged with bitumen; where it is, it is blackish, composed of fine grains of white quartz, cemented to- gether by a calcareous and clay paste; some layers in this bed were highly charged with foraminifera; the total thick- ness of this asphalt group of rocks here might be about 120 feet. Upon this reposed a layer of soft, white feld- spathic clay rock, in a state of minute division; in places so soft as to be readily cut with the knife; in others, hard and almost slaty; in places partly calcareous; in others, pure argillite, or kaolin clay. These beds were a little thicker than the foregoing, and perhaps were 200 feet in thickness. In these occurred the arca obispoana; of Conrad's report. As these beds were first encountered in this plain, and were afterwards found at several points along shore to the south, as far as Los Angeles, and as they are almost always associated with asphaltum, they will deserve a somewhat fuller notice.
The total thickness of these beds approaches Soo feet.
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HISTORY OF SAN LUIS OBISPO COUNTY.
From the Santa Lucia sandstones it is locally separated by the serpentine buttes and intervening valley. Its geological connection could not be traced at this point, the lowland and swamp of the valley occupying a large surface.
In the lower conglomerate no fossils were observed, nor in the yellow sandstone lying above it; the two upper beds contained fossiliferous layers, the asphalt rock con- taining the polythalamons shells, and the soft argillite containing impressions of arca obispoana, this fossil cast alone being found; while in other places, broken casts of fish scales, and dorsal spines of minute dimensions were found scattered throughout.
The upper thirty feet of this stratum is harder, and approaches a slate, readily splitting into thin lamina. This and the cream yellow tint, with the imbedded fossil, serves to recognize the bed.
The polythalamous layers were intercalated between strata of fine sand rock, made up of minute rounded grains of transparent quartz, not cemented, but adhering by cohesion; these could be separated at the edges by mere pressure of the fingers. Among the polythalamia, the forms of rotalina and orbicularia were the most abundant. I am inclined to look upon this series as the most recently elevated strata in California; the upper soft rock, which is the most persistent and easiest recognized, being the distinguishing stratum.
I have not observed them north of San Luis Bay, not having reached the coast north of that point. It is likely they extend along shore to Punto Gordo; the deeply excavated beach would imply some such soft rocks at the base of the Santa Lucia Range. From San Luis, south, they may be traced, by Nipomo, along shore, and occupying the low hills of the Santa Inez Range, at Point Concepcion; thence under the terrace at Gaviota Pass, and along shore, close to Santa Barbara, where it rises up to form a terrace cliff barrier 100 feet high.
From Santa Barbara it may be traced, not far from the shore, to San Buenaventura; and east of Santa Clara River, it leaves the shore, running directly east, and form- ing the upper beds of the low hills called Sierra Monica, whence they may be found running out north of the town of Los Angeles.
In the Santa Margarita Valley these strata were not observed occupying a prominent position-perhaps the center of the plain may be occupied by them-but they were found in the northern end of the Santa Maria Val- ley, where they form the latest beds of the San José Mountain on both slopes, and are found occupying a position superior to the ostrea and pecten beds, corre- sponding to those described in the account of Santa Margarita Valley. In the valley of Santa Maria River they were found traversing the base of the hills about 150 to 300 feet above the level of the valley; upon these layers the lowest hill terrace of the valley was placed. The strata extended twenty miles along the hills towards the head-waters of the river. This is the furthest point inland at which they were observed, about sixty miles from the sea. In this extended course (above 200 miles from north to south) they have a varied dip along the San José Range, whose axis is granite; they are unaltered in character, and have an elevation on the east side not more than 15°, while on the west it approaches 45°.
In the valley of San Luis the dip is 20°, while along the coast at Gaviota Pass it is 40°. Both in Santa Bar- bara and Los Angeles Counties it varies from 8° to verti- cality, in proportion to its proximity to the trappean and trachyte eruption. In the eastern end of the Sierra Monica, north of Los Angeles, the strata are almost vertical. Though not observed further north on this survey than Estero Bay, there is no reason to doubt of their occurrence in the valley of the Coast Range
further inland. From Dr. Trask's description I am inclined to think that beds found by him near the mouth of the Pajaro River, and those observed by W. P. Blake, near the town of Monterey, are extensions of those to the north. Dr. Trask notices that these beds, the two upper series of the group described here, are never found at a lofty elevation-that they are found above an altitude of 500 feet. This was also observed upon this survey, with one exception, the Santa Maria Valley. Everywhere these beds have been observed, they seem to have suffered extensively by denudation. In San Luis Valley, to the south, these strata merge into the Santa Lucia Range, and shut up the valley in that direction. Around the town of San Luis, and north to the ocean, these soft strata have been removed, and have left only the harder conglomerate standing here and there as land- marks to indicate the former position of the strata.
The history of these beds would be incomplete if notice was not taken of their occurrence upon the hills which form the divort between the Valleys La Purissima and Santa Inez. In descending this hill slope on the southeastern side, or entering the Santa Inez Valley, the upper yellow slate was met, forming the sides of a cañon, down which the wagon-road led to the valley; on exam- ining these shales, they were found to contain in places the impression of numerous bodies of small fish-only the marks of the vertebrae and ribs were discernible- the scales of which had only been obscured in the San Luis Valley and elsewhere; intermingled were some fractured impressions of dorsal spines. In the same locality was found very beautiful pecten discus; lower down the strata became black from asphaltic impregna- tion.
This description completes the history of these upper strata of the Valley of San Luis. In noticing them, as occurring in other places, reference is made to this local- ity for a knowledge of their characters to avoid repeti- tion. They are the most recent of the consolidated rocks of California. They have suffered the most extensively from denudation, and upon them, either on their edges or their slopes, the terraces and the raised beaches are found, and they are constantly associated with outflows of bitumen.
Between the serpentine and trappean upheaval, on the east side of San Luis Valley, and the conglomerates of the bituminous group on the west, the valley, proper is located; the surface is covered with alluvial clays, the whole depth of which cannot be estimated, as no borings have been made, and not more than twenty feet of red- dish yellow clays and light gravel were observed in the river courses. As the center of the valley has suffered so much from denudation, it is probable that the ancient alluvium is also very deep. The valley at present slopes slightly to the northwest, where it opens on the ocean, the direction doubtless which the denuded matters took when it was being removed from the plain.
SALINAS VALLEY.
The most prominent of the several valleys is that of the Rio Salinas. This valley, at its mouth, has a width of about nine miles, and extends sixty miles inland between the Salinas and the Gavilan Mountains. The lower portions of this valley are decidedly of a prairie or plain character, and are thus styled. They are quite like the lands along the lower Pajaro, flat and monotonous. Ascending the stream, the valley narrows, and losing its continuity, breaks up into tributary or lateral valleys. Of the lateral valleys, those -which come under our observation are the Estrella, Santa Margarita, Rinconada, and San José. The Estrella heads to the east of the San José ridge, and is separated from the Tulare Valley by a series of low, broken, and bold hills, the terminal spurs
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GEOLOGY.
of the Monte Diablo and Gavilan masses. This valley has an average width of over eight miles, and unites with the Salinas at San Miguel, having a meandering course of forty miles. The Santa Margarita and Rinconada are lateral valleys, uniting with the Salinas on its left bank. These valleys are somewhat basin-shaped, and receive the drainage from the eastern face of the Santa Lucia Range for a space of twelve miles, and all uniting in these basins, flow off easterly to the bed of the Salinas.
San José is above and to the southeast of Santa Mar- garita, and may be called the head valley of the Salinas. It partakes, also, somewhat of the basin character, but of limited area. Here are gathered the waters of the Santa Lucia and San José Mountains, the source of the Salinas forming a single stream, which, breaking through the rim of the basin, flows off through a tortuous cañon, assuming in its progress all the different phases of valley features, which finally resolve themselves into those of the plain below. Beyond San José, and separated from it by twenty-three miles of rough country transverse di- vides, stretching between the two longitudinal ridges, lies the Cuyama Plain, or the prolongation of the axis of the San José and Santa Margarita Valleys. This plain is about forty-five miles long, and has an average width of two miles. It heads near the Santa Emelia Mountain, and slopes off to the northwest, being drained by the Rio Santa Maria, which meanders through its length, and, reaching a barrier at its northern end, turns abruptly oceanward, and breaks through the Santa Lucia Ridge by a narrow and rough canon. The head of the Estrella Valley lies immediately on the east of the lower portion of this plain, and is separated from it by a low divide.
Still further to the east is found another remarkable feature, the Estero,* a broad, smooth plain, destitute of timber and shrubbery, cut off from the Estrella and Cuyama, and also from the Tulare Valleys, by low ridges. From a distance this plain had the appearance of a basin, having a broad and shallow lagoon near its center, whose waters were evaporated during the dry season, but, nevertheless, it has a drainage toward the Tulare Valley. [This is a mistake. It has no such drainage .- M. A.]
Crossing from Santa Margarita to San Luis Obispo, we enter upon the plain of the mission, extending from the base of the ridge to a low range of sandstone hills and bluffs, separating it from the beach, through which the waters of this plain flow off by a narrow valley to the ocean, at the port of San Luis, This plain was smooth and meadow-like, but of limited extent. Between the plain of San Luis Obispo and the valley of Santa Inez are found several minor valleys, whose streams break out - from the Santa Lucia Mountains and flow directly to the ocean. Of these the most important is the Guadalupe Largo, a plain which stretches from the base of the ridge in delta form to the beach, and contains about eighty square miles. The Santa Inez Valley heads in the angle embraced by the Santa Inez and San Rafael Mountain, and is drained by a stream which trends off in a westerly direction close under the former mountain. In its course this stream flows through a gorge for about twelve miles, separating the main valley into the upper or Santa Inez Valley, and the lower or La
Purissima, from the mission there located. These valleys have a combined length of fifty miles, and an average width of four miles, and are bounded on the north by terraces sloping back to low spurs jutting out from the mountains to the coast. The valleys and side slopes of the mountains and terraces are dotted with clumps of oaks, and the streams fringed with a growth of willow and cottonwood. Leaving the Santa Inez, no valley is
found until arriving at the mission of Santa Buenaven- tura, which is situated at the mouth of the valley of the same name, near the beach. This we crossed at right angles, but found, by side explorations, that it extends inland, and turning the east end of the Santa Inez Mountain, heading with the Santa Inez River, receives the waters of the ocean slope of a lofty ridge, the cx- tension of the Santa Lucia, which separates this valley from the head of the Cuyama Plain.
OF THE QUATERNARY PERIOD IN CALIFORNIA.
An interesting portion of the physical history of Cali- fornia is that which relates to the period immediately pre- ceding the existing date of things; a period subsequent to the deposition of the blue clays-the sand and gravels, with the coarser (local drift, the chief portion of which latter has since been removed), and anterior to the pres- ent physical configuration of the coast line. This period, when the present surface of California was an ocean, studded over with elliptical-shaped islands, which ran in linear meridional directions, with currents flowing between them and the mainland, was one of elevation, with per- haps occasional depression, and is one the history of which there are not materials sufficient to transcribe.
In the geological history of this coast, depression of the land does not appear to have entered largely as an element. There are no records of a continued slow de- pression, as evidenced elsewhere, by the carboniferous limestone of the Rocky Mountains, or of the jurassic beds further east; at those epochs it does not appear that this portion of the continent even skirted the mainland -far away out to the westward it formed the depressed bottom of an ocean whose shores were no nearer than longitude 110°, if, indeed, at that epoch, there were any summits of the continent front latitude 30° to 37 north, above the surface of the sea. So far out at sea was it that it does not appear that the granite bottom received much current deposits until the commencement of the tertiary era, when, by the elevation of the land, basins, estuaries, and rivers of greater magnitude aided in the formation of those sand and clay beds which have accumulated to so remarkable a thickness.
At the close of the tertiary period commenced the deposition of the thick, blue clays with broken shells; then the yellow clays and gravel, and, lastly, a bed of conglomerate drift, of mixed material, granitic and vol- canic materials, which upon one valley plain at least has been wholly removed. This drift is derived wholly from the degradation of the neighboring sierras, and contains no masses of rock which cannot be traced to the hills in proximity. The removal of this upper bed from the valleys of California has materially increased its fertility by diminishing the depth of the porous unconsolidated strata. East of the Sierra Nevada, in the Mojave Val- ley, the same unconsolidated strata are met with: also of granitic and volcanic conglomerate in the upper bed; but these have not been removed, and, like the Sonorian Desert, it is a barren plain which appears to have under- gone but little physical alteration since its final upheaval.
With the deposition of these quaternary beds, es- pecially of the upper ones, and with the corresponding periods of upheaval, are connected the system of ancient terraces, which are met with everywhere in California. Every mountain-side, every river-bed, and every valley of that State, presents the unmistakable evidence of a state of quiescence of the land with that of a gentle flow of water over its surface during the latter portion of the quarternary period, a period of deep estuaries and bays or straits, whose waters then reached points now nearly 2,000 feet above sea-level: or, in other words, when the land was so much depressed.
Notice has been made incidentally, throughout this re-
* Carrisa Plain.
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HISTORY OF SAN LUIS OBISPO COUNTY.
port, of the occurrence of these terraces, in describing the localities where they exist, and it is only necessary here to collect the observations together so as to form a connected series.
Commencing at the Salinas Valley three terraces have been noticed on its bed, and one on the sides of the San Antonio Hills, near the Mission San Miguel. On the Arroyo San Benito, a tributary of the Pajaro, which it joined near the village of San Juan, a little south of that village both sides of the stream have continued terraces for four miles; that on the east side, or right bank, being forty feet above the present valley level; that of the west side almost as high, differing only in a few feet from the others; the valley is not a mile across. This valley is one which leads out from Tulare Valley through the high range (Gavilan) separating them.
The pass leading from the Salinas Valley to Monterey is formed of the sandstones overlying the Point Pinos granite; at an elevation of 140 feet the summits of the low hills are flattened and covered with oaks; the terrace flat extends 100 yards back on each slope. This may have some connection with the terrace on the valley side of the San Antonio Hills, which are about twenty feet above the level of the stream. South of the Mission San Miguel terraces again are found on each side of the river bank, seventy feet above the river level.
On the west side of the Valley Santa Margarita a small terrace is found, twelve feet above the valley; on this eminence the old Mission Santa Margarita is placed. There were no terraces observed on the east side of this valley.
In the valley of the Santa Maria River some of the most extensive systems of terraces were found. These have already been noticed in full; they stood on the sides of the San Jose Range, at the height of thirty and 150 feet respectively; a terrace flat existed on the central insular elevation and a high terrace on the Santa Lucia Hills, above 150 feet high. Besides the hill terraces, the river bottom was cut down so as to form a well-marked terrace, the ancient or upper bed of the river.
On the east side of the San José Mountains in the Panza Valley, and the elevated land of Carrisa along the banks of the Estrella River, two sets of terraces were found, the lowest at twelve feet, and the upper seventy feet above the river level. It is remarkable how nearly the level of the upper terrace here and that of Santa Maria Valley assimilate, the one being 1,650 feet above the sea, and the other 1,676. The difference might, per- haps, be placed on an error of observation. In Santa Inez Valley the river flows in a narrow bottom, twenty- five feet below the ancient valley, in a direction toward the west; north of the ancient bottom, a terraced land spreads along its margin twenty feet above it; upon this the Mission Viejo is placed, behind which (N. W.) another terrace rises 100 feet above the last. These different levels are not distinctly repeated on the south side. The different ancient water levels are then :-
25 feet-Ancient river bed above which, at
20 feet-First terrace,
100 feet-Second terrace,
Above the present river level.
Leaving the inland valleys and taking the line of travel along shore, the whole base of the Santa Barbara Range, coastward, will be found to be one great terrace from Point Concepcion to Santa Barbara. As the latter place is approached, the terrace at the immediate base of the range is scooped out, forming a valley, in which Mr. Hill's ranch and the Indian village are situated. This terrace, in its whole length, averages eighty feet above the ocean level, toward which it presents cliff edges.
Ancient sea beaches have been observed at a few points in or near the shore. In San Luis Obispo County
one well-marked sea beach is found on the summit of a conglomerate hill which overhangs the west side of the valley a little south of Corral de Piedras; the summit height, 300 feet above the plain, was covered with fine quartz sand, mingled with broken and perfect shells such as exist on the shore a little west, as the Saxidomus Nuttali, a common shell along the coast. Another beach was found on the summit of a small hill which lies directly at the month of the San Luis River on its south- ern side, with similar shells; this hill had not an altitude much exceeding 150 feet. The shells found on it were precisely similar to those found along the present shore at the base.
On the terrace, a few miles north of Santa Barbara, deposits of fine quartzose sand with the broken shells indicated the existence of an ancient beach along its line, and similarly at the port of San Pedro along shore, where the cliff has been cut down for the improvement of the wharfage; besides the terraced flat above, which may be forty feet high, the cliff itself presents the follow- ing section from above downward: Alluvial clay and sand, ten feet; calcareous bed (beach) eight feet; arena- ceous clay, with modiolus, cardium, and small univalves, twenty-two feet, the strata dipping southwest. At another point of the custom house, a section slightly different was obtained; the distance between the two points might be 500 yards along shore, the strata dipping northwest. Alluvium, eight to eleven feet; raised beach, with shells, four feet; argillaceous rock, six feet; yellow and blue clay stratified, thirty feet. Accompanying the Venus Nuttali is a trochita, also very common along shore; these two shells form the mass of the perfect as well as of the comminnted shells of every raised beach along shore.
The following synopsis of the localities where terraces have been found, with their relative and absolute height, may serve as a conclusion to this brief notice of the evidences of rising land :-
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