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 61
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The superficial portion of the rock is soft, and feldspar crystals out distinctly from the paste; it is of a flesh- brown color externally, with a bluish shade on fracture, well seen on the south side of the harbor of Monterey, near the steamer landing, and thence to Point Pinos,
238
HISTORY OF SAN LUIS OBISPO COUNTY.
upon the low bosses forming which the light-house is built. It is probable that it is due to the alkaline nature of the soil, produced by the disintegration of the rock, that the cedar and sequoia flourish down even to the level of the sea, a point much below the usual altitudes common to those trees.
There the granite is nearly five miles broad, where it dips under the alluvium forming the low land around the inner harbor. Southward it extends in a line southeast, forming the chief mass of the mountain, occupying its western and highest ridge, until it reaches the River San Antonio. East of the granite lies a great width of ser- pentine rock running parallel with the granite and form- ing a sharp, narrow crested ridge, which, by its abrupt- ness upon the Salinas, hides the main granitic ridge from view when traveling along that river. Still, the presence of the granite rock is revealed by the wash of almost every mountain stream, which carries down a large por- tion of primary rocks among its debris. On the east of the serpentine lie talcose and chloritic slates, intersected by filamentous veins of quartz. These being the min- eral conditions under which gold is found, it was sus- pected that the precious metal might be found in this range. In the winter of 1854-55, prospecting was car- ried on to a small extent on the head-waters of the San Antonio, in the northern part of San Luis Obispo County. A few native Californians commenced washing there, and obtaining about $4.00 per day for each hand; the quantity, however, ultimately obtained was but small, and the washings were abandoned after a little. The protrusions of serpentine and magnesia slates drop down before the range approaches San Miguel Mission, and do not appear again. The fossiliferous sandstones, with dosinia underlying the Salinas River, rest on these, have been upraised by them, and are in places rendered met- amorphic by contact.
The granite itself drops down, as stated, and while diminishing in height covers a greater breadth to the east. Owing to the close approach of the magnesian rock to the river valley, the trail is obliged to leave it and cross the eastern portion of the range, where it meets with the San Antonio River, which rises in the granitic hills further north, and passes in the small trough between the serpentine and granitic ridges of the mount- ain. This trough is filled up by the fossiliferous sand- stones which here dip to the southwest, being influenced by the serpentine upheaval rather than by the granitic, the latter being the rock first elevated. The sandstone is in places converted into a rock resembling novaculite, and near the Mission Soledad beds of jasper and reddish porphyritic rock are found. Angular fragments of prase occur in the arroyos which found their way into the val- ley; a bed of conglomerate lies below the sandstones. This stratum is of a greenish tint, and contains pebbles of hayaloid quartz, prase, serpentine, and porphyry. It was not fully exposed, so that not more than forty feet of thickness could be attributed to it. Above, this sandstone is whitish, a soft rock, easily degraded, and fossiliferous. The dip of this upper bed is very variable, dipping in every direction, east and west, and occasion- ally vertical. It appears to have suffered considerably by the talcose upheaves and by subsequent denudations, the terraces which are found at the base of the range being covered with angular fragments derived from the degradation of these strata. The fossils of these strata are described elsewhere in this respect. The total thick- ness of this upper bed is about eighty feet where ob- served. The sandstone which lies beneath this are of two kinds, brown and red. The brown beds are soft and easily decay; the other bed is made of white quartz grains in a reddish paste. This bed is not fossiliferous, but at several points between the Mission Soledad and
San Miguel, these two bands of sandstone were sepa- rated by a calcareous stratum, whitish, and in places fif- teen feet thick, with particles of comminuted shell, and casts of dosinia alta, and obliqua, and a small venus. Above both sandstones were found, near San Miguel (south) occasionally cropping out, ostrea, hinnites, and pallium; but few specimens could be collected complete, owing to the brittle character of the fossil, from disloca- tions of the rock; the fossils are, however, noticed in full when describing Santa Margarita Valley.
From the outline it would appear that the structure of the chain is simple and may be stated as follows, com- mencing west with the axis, and traveling east :-
WEST-granite one and one-half to five miles wide; serpentine, talcose, and chloritic slates; green conglomer- ates, sixty feet exposed; brown and red sandstones with dosinia, 200 feet; soft white calcareous; conglomerate ostrea, fifty feet east.
Upon the latter two series the terraces are placed south of the Mission San Miguel, and east of the Valley Santa Margarita the San José Mountains proper commence. Those hitherto treated of are the geological extension northward.
At Santa Margarita, the Salinas River flows on the east side of the valley; there is a collection of granitic hills from 600 to 1,000 feet in height, set close together, with deep cut gorges between. This granite occupies a breadth of six miles from the Salinas, eastward, when it disappears under the elevated sandstone of the Estrella. On the slopes of this granite occur tertiary sandstone, similar to the fossiliferous beds of Santa Margarita. Running in a direction south 48° east, it attains a high elevation, and twenty miles south-east of Santa Margarita is almost 3,000 feet, its greatest probable height; it pre- serves its height for nearly fifty miles further south, where it forms the eastern edge of the Cuyamas plain, sepa- rating the latter from the shallow basin of the Estero and. from Tulare Valley. As a mountain range it is there lost. It may be traced, geologically, in the porphyritic hills separating the upper waters of the Santa Maria from those of Tulare, or from the Great Basin, and becomes con- founded with the mountain mass of San Emidio.
In this portion of its course the chain has an axis purely granitic, either feldspathic granite or gneissose rock. South of San Miguel there is no longer any parallel ridge of serpentine, any talcose or chloritic slates. The mag- nesian rocks are wholly wanting, and are only represented by the addition of hornblende to the granitic rock, which gradually creeps in the further south the range extends, entering largely into the gneissose portion, and rendering the whole rock more compact. Mica is still a mineral lit- tle abundant, the feldspar predominating, which is some- times bluish from adularia, and sometimes cemented by a paste of epidote. The feldspar in the northern range is flesh-colored, and contrasts strongly with the clear green of the epidote, giving a porphyritic appearance to the rock.
The granites of this range are wholly of the first system, containing the highest amount of oxygen in them, and are mostly of the formula of orthose, which is found of a whit- ish color, and in rhomboidal prisms in the northern por- tions of the range. In San Luis and Santa Barbara Coun- ties the orthose crystals are usually in hexagonal prisms, with dehedral summits of a flesh-color, approaching a brick-red; the quartz in amorphous pasty masses, very few crystals of brown mica interspersed, and a large amount of the paste is of serpentine, which gives a greenish tint to the whole rock, contrasting strongly with the colored feldspar. In the interspaces between the lines of fissure of the blocks a coating of amorphous carbonate of mag- nesia covers the surface of the granite. In Santa Barbara County hornblende enters into the granite very largely, giving it more the appearance of hornblende porphyry
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GEOLOGY.
than a true granite. The amphibole mineral appears to replace the serpentine. Gneiss, which is rare in the State, is found in the rolling country east of Cuyama Valley, where it is met with in the bed of the stream Carrisa, and occupying a width of several miles of the undulating land east of this range; the gneiss is hornblendic, and accompanies the granite in its further southern course, keeping on its eastern edge until this sierra merges into the mass of San Emidio and the country round about the Tejon. The gneiss was cut up in several places by dykes of granite in the vicinity of Panza Rancho. The sedimentary strata dip, both east and west, from this axis, which through its whole course has tilted the strata on its western side to a much higher angle than those on its eastern, the latter country being the much higher ground. In crossing from the Santa Maria River at Cuyama Valley, eastward toward Carrisa, the ascent is toilsome and precipitous across strata, some of which are at an angle of 70°; the bed next to the granite, a green- ish conglomerate, standing with its weathered pinnacles almost erect, forming the lofty and prominent crest of the range, which then drops down by slow descent over rounded granite hills until, after a few miles, the sedimentary strata are again met with, dipping in an opposite direction at an angle of not more than 25° to the northeast, which drops gently into the upland swells of Carrisa.
This chain was crossed in two places for several times, viz .: At Camp 19, in the Valley San José, and again about twenty-five miles further to the south, to enter Cuyama Valley. The strata presented to view differed but slightly in the two places, viz .:-
A .- Section of crossing from camp in San José to Panza.
ON WEST SIDE.
GRANITE.
DIP.
THICKNESS.
I. Green grits and conglomerate ... . 2. Coarse porphyritic conglomerate.
64° to 70° SW. 56° SW.
150 feet. 200 600 “
4. Conglomerate of serpentine and quartz pebbles. . .
50
5. Whitish sandstones and layers of argillite, with gypsum; remains of ostrea and Pallium.
45° SW.
250 4
Total
1, 250 feet.
ON EAST SIDE.
I. Green grits ..
2. Coarse porphyry conglomerate .. .
3. Brown and yellow sandstone.
4. Serpentine conglomerate.
35° NE. 20° NE. 15° NE.
300 feet. 500 4 80 “
5. Gypseous beds, with argillite
200
Total.
1,080 feet.
B .- Section crossing from Cuyama to Carrisa.
ON WEST SIDE.
GRANITE.
DIP.
THICKNESS.
I. Grits and green conglomerates.
35° S., 75° W.
2. Yellow arenaceous grits ..
3. Brown sandstones and shales ...
4a. Reddish conglomerate of jasper.
4b. Fine reddish grits, with gypsum.
22° SW.
200 "
5. Gypseous sandstones, with os- trea and calcareous beds ...
15º S., 60° W.
75 €
Total.
975 feet.
ON EAST SIDE.
I. Green conglomerate. .
2. Brown and yellow sandstones.
3. Reddish conglomerate ...
4. Gypseous sandstones, with calca- reous layers, containing ostrea and argillite beds superimposed.
IOº NE.
400 “
Total (observed).
860 feet.
As the figures expressing the thickness of the strata are only approximative, they may be somewhat under- estimated; they show, however, that on the eastern slopes of the axis the deposits are thicker than on the western. This thickening is independent of any elevating cause. The yellow sandstones are thicker still further to the east, on the Panza Hills, than they are found upon this range, indicating the source of deposit to be toward the east. The contact of the green conglomerates with the granite rock was frequently observed in these hills; the only rock which at any time separates them was hornblendic gneiss, which, on the east side and toward the south, intervened. No metamorphic rocks, no doubtful schists, were here; no silurian or palæozoic rocks. The crystal- line and metamorphic limestone which occasionally lies next the granite, as on Mount Diablo, Gavilan, and the Cordilleras of Los Angeles and San Bernardino, are wanting, and nothing but tertiary sandstones, efflorescent with gypsum, and cut through with thin seams of brown peroxide of iron, conglomerates of magnesian origin, and those of jasper and porphyry, with superimposed beds of fine sandstone and clay, highly fossiliferous, con- stitute the stratified rocks; these average 1,000 feet in thickness.
The green conglomerate bed is the most persistent of the whole group, being made up of rounded frag- ments of serpentine, chlorite, and trappean rock, ce- mented by a brown aluminous sand, and found in close proximity to the granite; it occupies the highest points of the range, and forms the pinnacled summits which serve as good land-marks from a distance. The red conglomerate bed is made up of fragments of jasper and brownish quartz, with obsidian, and occasionally amyg- daloid green stone, as these latter rocks are found more abundant to the north and east.
ESTRELLA RIVER, PANZA, AND CARRISA.
The San Jose Mountains separate the Salinas and Santa Maria Valleys from those lying further east. When this range is crossing east of Santa Margarita, or of Cuyama, a valley country is entered whose elevation is considerably above that of those on the west; but the nature of the valley north and south are very different in character. At the point where the San José chain crosses the Salinas to pass south, the San Juan, or Es- trella, River enters the Salinas. This, which is hardly a tributary, since it is much longer than the upper Sa- linas, takes its rise forty miles further southeast in a series of high valleys on the eastern base of the San José Mountains. The stream, there small, receives the name of Carrisa Creek, where its elevation is more than 1,600 feet above the sea; as it passes south, it leaves the open, rolling sandstone land and enters a narrow valley wonderfully disturbed since its deposition, and denuded during its elevation. This receives the name of Panza Valley, from the ranch of that name. North of this it receives the name Estrella, and from thence north- ward the river retains its place at the base of the range until it reaches the Salinas Valley and River.
The region of Carrisa was but little examined; but few fossils were found in the upper sandstones; in an upper layer of these, before reaching the valley of Panza,
30° SIV.
700 feet.
Not observed. 20° NE.
400 feet. 60 “
3. Brown and yellow sandstones. .
240
HISTORY OF SAN LUIS OBISPO COUNTY.
two small shells were picked out of the soft sand rock. These were pecten deserti (Conrad) and anomia sub- costata, the latter doubtful, the former is a shell found on the western limit of the Colorado Desert; it is here found 250 miles northwest, and separated by two valleys and three mountain ridges. The stratum does not correspond lithologically with that of the desert in which it is found.
The granitic axis of the San José Range spreads out westward underneath the strata elevating the whole plain, and carrying the sandstones to a level several hundred feet above the western valleys. Nor does it merely ele- vate; it is also itself protruded in several places, not in a chain, but separately, producing the local disturbances and flexions of strata alluded to. Panza Hills, lesser and greater, are two mountains which display these phe- nomena well, being masses of granitic rock at their southeast end, which have tilted up the strata, and causes them to dip toward the San José, from which they are not distant further than six miles in an air line eastward. Further south, the country still rises with rolling hills of sandstone, presenting their worn edges to the west and south. The granite appears more con- stantly as a surface rock, and along the head of Carrisa Creek gneiss is traced for several miles accompanying the stream. This elevated, rolling plain stretches several miles to the east where it drops down into Tulare Val- ley. This lofty district owes its elevation to Gavilan Range, coming in at this point in its southern course, and intermingling its strata with those of San José. The result of this union of two parallel ranges not only pro- duces the highly elevated country, but, perhaps, also the increased elevation of the San José Range itself, which, at this point, the head of Carrisa Creek, sustains a loftier crest than elsewhere in its course. South of this point the two ranges separate and pursue different courses, forming, by their divergence, Estero Plain, a wide trough plain, with a gentle descent to the south- southeast, where it opens into Tulare Valley by the sub- sidence of the Monte Diablo Range at the extreme south.
Estero Plain is a miniature of Tulare. The hills bounding in on either side supply it with water, small in quantity, which collects in lagoons, or ponds, in the cen- ter, and thence flows sluggishly south, forming the Agua de Paleta, which rolls into Buena Vista Lake, in Tulare Valley. The northern edge of the plain near Carrisa and Panza Hills furnish the largest amount of water, as many as three distinct streams being observed to roll down to the lake in the center of the plain, which is uninhabited by man, and occupied only by herds of deer, antelope, and wild horses, with which it abounds. It is about forty miles long, and averages twelve broad. Nothing exact is known of the geology of this plain. Its geography was comprehended exactly by looking from the summit of Panza Hill, which overlooked the whole country, south and east, as far as the eye could reach. The southern portion of the plain was again observed in crossing from Tulare to Cuyama Plain; of its structure nothing more is known than that its eastern ridge is the Monte Diablo Range, terminating south at the head of Tulare Plain-its western, the San José Range; the sandstones slope into Estero from either side. Two slight elevations cross the plain above and below the lake, as if a dyke crossed in these places. The plain itself was not entered.
In treating of the San José Mountain Range, allusion was made to the axial and sedimentary rocks; the textural character, dip, and thickness of the strata on its vastern side are there given, and need not again be re- peated. Hornblendic gneiss appears here upon the vast side of the range along the bed of Carrizo Creek
for some miles down below its source. It presented the appearance of a stratified rock dipping away to the northeast. Although the granitic rock was exposed to a few points east of the range, yet nowhere was the gneiss rock observed in contact with it there. Panza Hills are sandstones, elevated by feldspathic granite, which occu- pies low bosses on the southeastern edge of the hills, and have no gneissose rock, nor any appearance of the limestones found at Gavilan; the point of contact of the sedimentary and upheaving rocks was not, however, observed. The lowest rock was a series of brown sand- stones, with sharp, angular outlines, and serrated and triangular shaped crests, in every respect similar to the lower beds of the Santa Barbara; above these were coarse conglomerates and grits with saline gypseous veins, and thin layers of limonite. These represent the beds on the east of Santa Margarita Valley, immedi- ately below the ostrea and scutella beds; these also line the Santa Lucia Mountains; then followed fine-grained sandstones with ostrea and pecten; and, finally, where the hill drops down to the creek bottom, fine arenaceous clay beds consolidated, containing arca obispoana. Both the northern and southern Panza Hills have a similar structure, and dip southwest from twenty-five to thirty- five degrees. The total thickness of these beds ap- proached 1,100 feet; the dip is towards the San José Range, from which it is separated by the valley interven- ing; this valley (Panza) like that of Santa Maria, is also one of denudation, presenting terraces 100 feet high on the east side of the San Jose Range, where the foot-hills run out into promontories, which, before the denudation, stretched across the present valley to the Panza Hills; these promontories come off from the main ridge like the teeth of a comb, and are themselves merely frag- ments denuded. On examining the strata of these terraced promontories near the edge of this valley, they are found to dip away from the valley and towards the range of which they seem to be a part. From one of these was obtained some of the finest specimens of the astero- dapsis of a larger size than those found in Santa Marga- rita Valley. Accompanying it was the scutella subro- tunda, the pecten, and ostrea. The dip of these layers was fifteen degrees southwest. On another promontory, above a half a mile up from the valley, yellow clay rock containing the same fossil scale impressions as that found on the shore at the Gaviote, and also found on the west side of the San José. The green agatic quartz riband layers found in Santa Margarita Valley were not found here.
The exploration of the Panza Hills proved to be very interesting; their sandstone, less inclined than either those of Santa Margarita or Santa Inez, allowed of a comparison not admitted by the others. The continuity and relative position of these beds could be better studied there than in any other locality. Here was first observed the angu- lar-crested gypseous sandstones repeated at Santa Inez, and here was observed the relative position of the ostrea and echinoderm beds, similar to those of Santa Margarita, with the softer clays and beds associated with bitumen along shore, and including polythalamous layers. Much that was doubtful was thus removed, and the relative posi- tion of these tertiary beds was thus determined to stand in this order from above downwards :--
A. Fine yellow slates; soft argillitic layers, with area obispoana; bituminous sand rock, with polythalamous layers.
B. Yellow sandstones, with pallium, ostrea, hinnites, and echinoderm.
C. Brown and yellow grits; sandstones conglomerates, gypsiferous and ferruginous; the upper beds including the dosinia of San Antonio.
241
GEOLOGY.
D. Coarse grits and green conglomerates of serpen- tine and jaspery quartz.
The last bed, so distinctly marked on the San José and Santa Lucia Ranges, was not observed represented on Panza Hills, in which circumstances it resembled Santa Inez Range.
South of the larger Panza Hill, a few miles along the valley, a dyke of augitic rock, of a dark green compact structure was observed running north 80° east, and con- verting the sandstone into a hard, micaceous rock in its neighborhood; the strata dipped in every direction near it, and even the gneiss rock was slightly disturbed from its usual easterly dip. A folding together of the sandstones was observed not far from this on the river-side, causing a partial synclinal axis, which may, perhaps, have been produced by the upheaval of the Panza granite at a date subsequent to the elevation of the San José rock.
The bed of the Estrella River, at Panza, displays a series of terraces on the hills on either side precisely similar to those on the Santa Maria, although necessarily on a much smaller scale.
The fossils found in the strata on the sides of the val- ley were the following, the names and descriptions of which have been supplied by Mr. Conrad :-
I. Ostrea Titan. 7. Cyclas permacra.
2. Ostrea Panzana. 8. Cyclas Estrellensis.
3. Pecten discus. 9. Glycimeris Estrellensis.
4. Pecten Heermani. Io. Balanus Estrellensis.
5. Pallium Estrellensis. II. Asterodapsis Antiselli.
6. Sponchylus Estrellensis. 12. Scutella Subrotunda.
The ostrea, asterodapsis, balanus, scutella, and pecten, were found in the same strata and accompanying each other; the other fossils occupied the sandstones lying below the upper calcareous layers, having the commi- nuted shells and other points of resemblance with the beds containing ostrea and hinnites of Santa Margarita. The Panza beds are thicker than those of Santa Marga- rita, and more variety in the animal life contained in them. Like the latter beds, the Panza strata lie upon the slope of the San Jose Range, and have suffered ex- tensively from denudation.
VALLEY OF SAN LUIS OBISPO.
The valley or plain of San Luis Obispo is separated from that of Santa Margarita by the Santa Lucia Mount- ains; between this range and the Pacific Ocean is a plain in which the village of San Luis Obispo lies, and from which the plain derives its name.
The level of this valley is much below that of Santa Margarita, its altitude not much exceeding 150 feet; it slopes gradually to the ocean, from which it is separated by a range of hills which stretch from the shore to a dis- tance of six miles inward; these hills do not exceed 600 feet high, and dip variously in opposite ends of the val- ley; about the San Luis River, which finds its way to the sea through a break in them, and from thence south- ward the strata dip toward the shore, while in the north- ern part of the valley these strata dip toward the valley. This different dip is caused by the serpentine and trap- pean protrusions, which are the elevating rocks of the valley, passing across the strata in an oblique line from northwest to southeast, not producing anticlinal axes, but simply lifting the beds to the east at the north end of the valley and to the west on the shore. The consequence of this different dip is evident by inspecting the cost line, north of the bay of San Luis, where the dip is to the east, and the lowermost beds of the series are ex- posed; these are hard conglomerates of a greenish tint, arising from pebbles of serpentine and trappean rock, and have a dip from 15° to 20° S. 35° E. Here the strata stretch out into the sea "and form bold headlands,
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