Chapter III: Part 3

The most interesting geological feature about this northwestern part of San Diego County is the long plateau, confined chiefly to the Santa Rosa grant. This plateau lies near the western corner of the grant, and extends east nearly to Murrieta. The lava is broken up into detached tables by erosion, which become very strongly pronounced toward the western end of the flow. The western body of lava is the highest. It has a length of nearly 2 miles and is broken into three peaks or ridges, sloping generally a few degrees to the east; height 2,850 feet. There are two terrace-like tables lower down its southern slope. The lava is, perhaps, a hundred feet thick at its eastern end, and has been so much eroded toward the western portion that the underlying sandstone is exposed along the crest of the ridge, with lava lying in broken masses along its sides. The sandstones form quite an extensive bed under the lava flow, being 200 or 300 feet thick, and horizontally bedded, wherever bedding is present. The upper part is very soft and granular, the lower portion is hard and stained reddish. It carries many bowlders 6 to 8 inches in diameter, different from any other rock seen in the adjacent mountains: quartzite mica schist, aphanitic rocks, and some granitic ones. These are washed smooth. The sandstones contain much kaolinitic matter, and at one spot show an incipient crystallization. A number of contiguous grains, over a space half an inch in diameter, show the same orientation. Near the bottom the sandstones are impregnated with iron. The western ridge in particular shows a great amount of erosion. The lava is nearly gone in places, but occurs southward in scattered outcrops for half a mile. At the northern end the sandstone rises fully 300 feet above the lava. Lava is present on its sides. Much of the sandstone closely resembles a granite decomposed _in situ_. Fragments of the mica schist resemble that in the hills west of Temecula. Northward half a mile is the deep cañon of the San Mateo. The country descends very rapidly from the lava ridge, especially so on the north, where the cañon is fully 1,500 feet deep. It is a number of miles in any direction to mountains which are as high as this lava-capped sandstone ridge, and the amount of erosion must have been enormous since it was deposited. Mesa Redonda has an elevation of 2,750 feet, and is separated from the lava just described by a valley fully 800 feet deep, and nearly a mile broad. Mesa Redonda is formed by a lava table, probably basalt, 150 to 200 feet thick. It is quite precipitous on three sides. The lava is bedded, dipping 5° to 8° northeast. Underneath is a body of coarse, friable sandstone, similar to that just described. Some pebbles and bowlders of lava lie in the upper portion of the sandstone. The sandstone consists of angular quartz grains and kaolinic matter, and often presents the appearance as if it had been partly fused by the lava. In the top of the sandstones are pebbles of quartz, feldspar, and mica schist. The sandstone shows no bedded structure, but seems to form a mantle over the hill, following the irregularities of the underlying granite. It descends 700 feet on the southern slope of the mountains which rise so abruptly from De Luz Valley. The lava has spread out in thin sheets on the southern slope of the mountain, descending more than a thousand feet on the east side of Cottonwood Creek. These thin beds are not massive, but are formed of angular lava bowlders. The flows were so thin that they either broke up on cooling, or later through atmospheric agencies. Fig. 15 is a sketch of Mesa Redonda from the north.

Cienega Peak lies east of Mesa Redonda and is separated from it by two gulches opening in opposite directions. It has an elevation of 2,400 feet, and the mesas east rise still less. Sandstone underlies this as it does the other lava flows. Near the eastern end of the southern slope, a lava flow has broken out from a basin-like depression which opens southward, and flowed down the mountain for a mile, descending a vertical distance of 1,800 feet. It appears to have broken up entirely into angular bowlders. The stream was probably very liquid, like the others, and formed a thin flow. It takes a slightly winding course and slopes often 30°. One short branch appears on the western side about half way down, and another on the east near the bottom. The lava descends in successive terraces, like steps, from the crater depression. The width varies from 500 to 700 feet, terminating in a straight line about a hundred feet above the bed of the cañon at the head of De Luz Valley. This distance may represent the amount of erosion since the stream flowed. There are also cañons worn to some depth on each side. The surface of the flow is rounding, and appearances indicate that it descended over a surface not much different from the one now shown. A large part of the bowlders in the creek for several miles are lava. Fig. 16 shows this lava stream as it lies on the mountain side, and also Cienega Peak, from which it flowed. These lava beds appear very prominent from De Luz Valley. The long, winding flow is known locally as the Oak Ridge, on account of its being covered with oaks, while the adjacent mountains are barren and brushy. It is hard to reconcile the appearance of these isolated peaks, with often precipitous sides, and deep valleys between them, showing a great amount of erosion, with the thin sheets spread out on the southern side of the mountain in so many places, which from their position indicate so little erosion since they flowed. It is possible that the mesas, with the high precipitous cliffs, represent remnants of an older flow, and yet the lithological character of the lava seems to point to a single origin. With the exception of the long southerly flow and another short one west of it, the lava everywhere presents bluffs on its southern side, with deep gulches between them. Toward the northeast and east there is a gentle slope. A large part is coarsely vesicular; dense massive portions are mixed irregularly in places with the vesicular. The lava table-lands lie nearly 2,000 feet above De Luz Valley. This abrupt escarpment extends east as far as the lava does, though less marked. There has either been an enormous erosion in the region lying south, or a great fault elevating the plateau. A detached portion of the lava plateau caps the hills west of Murrieta, extending in a north and south line for a distance of 2 miles. Whether these detached portions all had their source in one great flow and have been separated by erosion, or were formed from different sources, was not fully determined. It seems probable, however, that the main portions did belong to one flow, from the fact that they have a uniform slope and are underlaid by similar sandstone, which may once have been the bed of a stream.

The range of mountains lying west of the valley which extends from Temecula to Elsinore, also has the appearance of having been elevated by a fault. From the entrance to the Temecula Cañon, northward past Elsinore, and along the eastern base of the Santa Ana Mountains, these abrupt escarpments and indications of a fault become more pronounced. The eastern part of the Santa Rosa plateau, with its lava fields, forms the southern end of the escarpment. The valley in which are located the towns of Temecula, Murrieta, and Wildomar, rises gradually toward the east. The western portion is very fertile. Artesian water is found at Murrieta. The eastern portion, which rises toward the granite mountains, is more gravelly, while east of Temescal there is a stretch of many miles of these dry gravel hills, probably of Quaternary age. The town of Temecula has an elevation of 1,000 feet. Immediately west and north of the cañon there arise hills of metamorphic rocks, having an elevation of 1,800 feet. They are covered with dense brush on their eastern slopes, but contain some fertile valleys to the west. For several miles the rock is almost wholly metamorphic. It extends south to the cañon and north to the lava plateau. It is chiefly a fine, dark mica schist; strike indistinct but north 60° west, to east and west, dip vertical. On the west it changes to a quartzite. Dikes of granite cut this rock; one is noticeable for several miles by its more pronounced croppings over the hills.

East of Murrieta the granite begins near the boundary of the grant, and forms a line of barren hills extending northerly. East of these the country is less rocky and quite fertile. Many springs abound in the granite through this section. Near the Hot Springs is a dike of granite porphyry. Numerous bunches of a dark, coarse, dioritic rock are scattered through the light-colored country granite. They weather away more slowly than the granite. The metamorphic rocks of the Santa Rosa plateau extend north to the entrance to the cañon, up which the road passes to Parker Deer’s. The strike in the cañon is a little east of north. The metamorphic rocks terminate in a range of hills which form the southern boundary of the Rinconada. Northward the country is formed of rugged granite mountains. The Los Alamos opens westward into deep cañons, which lead down to the coast. A dark dioritic granite is included in the usual light-colored variety, sometimes in bowlder-like masses and sometimes in dike form. The metamorphic rocks extend 2 miles west of Parker Deer’s house. They include mica felsite and dark vitreous quartzite. They are often intruded by granite bosses and dikes of quartz porphyry. The lava table-land lies just south of the ranch house. It is about 40 feet thick, and has underneath a kaolinic stratum 12 to 14 feet thick, which is impregnated with bog iron; one assay has shown 10 per cent. This is quite similar to the sandstone under the table-land farther west, but is less quartzose. A similar deposit, impregnated with iron, was seen north of Mesa Redonda. The Santa Rosa grant consists chiefly of broad, open valleys, having an altitude of 1,700 to 1,800 feet, with rocky ridges between them.

On the trail from Santa Rosa to Howe Station, the metamorphic rocks extend to within a mile and a half of the latter place. They are chiefly light-colored, granular quartzites. Dikes of diabase and gabbro appear in many places on the Santa Rosa grant. Ores of gold, silver, and copper are found in the metamorphic rocks of the grant, but they have never been developed. Selected samples of galena assay several hundred dollars to the ton in silver. The veins are, however, small and bunchy, and it is not probable that they can be profitably worked. The granite varies from one with mica, as the only dark constituent, to one with much hornblende. It is uniformly coarse and of undoubted eruptive origin, judging from the manner in which it has broken through the metamorphic rocks.

The table-land west of Murrieta is about a mile broad and fully as high as that near Parker Deer’s house. It is separated from the lava farther west by a mile of brush-covered hills. The lava was supposed to extend no farther than the big cañon west of Murrieta, but a close examination revealed a small outcrop on the hills about a mile south of Wildomar. The elevation is about 600 feet above the valley. It is perhaps one fourth of a mile across. In places it extends down the hill nearly one third of its elevation above the valley. It presents the appearance of having flowed out of the summit of the hill when it had much the same form as now, and down over its sloping surface. This eruption is fine-grained, and not vesicular. Much of it has a conglomeritic character, appearing to have been broken up when almost solid, and then cemented. The fragments are more or less rounded and elongated, and are at times almost blended in the matrix. There are signs of former solfataric action on the summit, there being a considerable deposit of a light yellowish material, consisting chiefly of alumina and magnesia. Under the lava is sandstone 10 to 20 feet thick, composed of quartz grains and kaolinic matter, exactly similar to that under Mesa Redonda. It would be easily taken for granite decomposed in situ, but for the large quartz grains. The sandstone has an apparent southerly dip. It is very difficult to account for the presence of the sandstone under the lava, unless we suppose it covered the adjacent country, and was only preserved by the greater permanency of the lava. Another hill of lava was found 200 feet lower, about a mile south of this, and west of the cañon leading up to Parker Deer’s. It occupies a sort of depression between three hills, with gulches cutting into it between them. The lava is very similar to that just described.

A long, high ridge running northwest and southeast, adjoining the lava, is very interesting. It is about 200 feet higher, and covered with dense brush, as is all the country in this vicinity. The greater part of the hill is formed of a coarse tuff, whose fragments stand out in sharp relief on the surface of the huge projecting, bowlder-like masses. The matrix, which is darker and softer, weathers out, leaving the surface of the rock covered with a great variety of fragments. Some are scoriaceous or amygdaloidal, others are very coarsely crystalline and porphyritic with feldspar or hornblende. Some of the fragments are themselves tufaceous, containing large masses of hornblende in a dioritic matrix. On the southern end of the hill, a great variety of dikes intersect the tufa. This is in all probability the neck of an old volcano, but appears to have no relation to the modern lavas near it. Owing to the exceeding difficulty of traversing these hills, the exact relations of the formations were not ascertained. About 10 miles east of Temecula, near the point where the creek takes a turn to the southeast and enters a cañon, there has been another lava eruption, but the time at my disposal did not permit me to examine it. A great variety of rocks are exposed along the road from Elsinore to Menifee Valley. For nearly 2 miles east of the station the rock is a white, glassy diorite, with an excess of feldspar. At the point where the road crosses the railroad, metamorphic schists appear. The rock is a fine, dark mica felsite. It is so compact that it breaks with a conchoidal fracture. A great irregularity in strike and dip exists; the average strike is a little west of north, dip northeast. As far as the top of the grade, the rocks are in part metamorphic and part dioritic. There are many dikes; some fine-grained granites, others micaceous diorite porphyrites. The hills along the west side of Menifee Valley seem to be mostly metamorphic, with some bunches and veins of granite.

All of the mountainous region lying south of the road from Temecula to San Jacinto is granite or diorite, excepting a strip of micaceous schist and gneisses near Glen Oak Valley. These strike northwest toward Menifee.

No opportunity was given me to examine the mountainous regions comprised in the San Jacinto range. The line of hills lying northeast of the town and having a northwest direction are composed largely of gneiss and mica schist, with some bodies of white crystalline limestone. In the line of strike these hills finally disappear north of San Jacinto Lake, under Quaternary clays and gravels, which form rather an abrupt rise from the San Jacinto Valley and extend northerly to the San Bernardino Mountains. The deposits show a great deal of disturbance. A part of them may be Tertiary. Dikes of dark, heavy diabase and diorite are common about the sulphur springs north of San Jacinto.

The hills for a distance of 3 miles north of Elsinore are formed of slate and mica schists; strike north 70° west, dip vertical to 45° east. This is a continuation of the same series of rocks exposed on the road to Menifee. A lenticular body of limestone occurs in these slates about 3 miles north and east of Elsinore. It is highly metamorphosed, has a gray to dark color, and is traceable for 500 or 600 feet. At one spot a stratum of quartzite divides it. It was carefully examined for fossils, but none were found. About 4 miles from Elsinore granitic rocks appear, followed by dark diorites in the vicinity of the Good Hope Mine. The Pinacate district, taken as a whole, is rather peculiar. At first sight it seems to be formed of granite, dark diorite, gneiss, mica schist, and other metamorphic rocks, arranged in the most irregular manner. The belt of metamorphics northeast and east of Elsinore is terminated on an irregular east and west line by these granitic bodies, which inclose portions of the schists, and extend into the main body as long, dike-like arms. In the vicinity of the Good Hope Mine the strata of metamorphic rocks inclosed in the granitic rocks have a north and south strike, and are traceable for a mile or more. The veins of the Good Hope Mine are in a dike of light-colored biotite granite. It has considerable width on the surface, 100 feet or more, but below ground some distance it is not over 12 feet. On the surface it is greatly decomposed and cut by numerous small veins, which are so scattered that they hardly pay for working. Below they unite to form larger veins, generally one on the foot and another nearer the hanging wall. The latter is more irregular, often running out at a small angle. The foot wall, a dark compact diorite, is very regular. The walls are separated by well-defined clay seams from the vein matter, the decomposed granite. Clay seams also separate the different veins. The foot wall diorite forms the country rock indefinitely eastward. The hanging wall is a fine, dark brown mica schist. The quartz is generally friable, and the granite vein matter much decomposed. The quartz at a depth of 300 feet carried one third of the gold in the sulphurets. A small amount of silver is also found. This vein is located for over a mile; direction a little east of north, dip 65° west. It is remarkable that there is no barren quartz; all the ore pays for working. In the lower workings the veins become more regular.

The Good Hope is the first mine in this district to reach a paying basis, and that has succeeded in finding a regular, defined quartz ledge. About 3 miles northwest is another vein, which has an east and west direction. It seems to lie wholly in granite, save for a narrow stratum of mica schist on one wall. The vein is located for a mile, but no extensive development has yet been made on it. On the hills, a short distance southwest, is an old Mexican mining camp. Many small veins are found in the vicinity, generally in a dark micaceous diorite. There are also bunch-like masses of coarse white granite, blending into gneiss and the gneiss into mica schist. The strike is exceedingly irregular, changing from north and south to east and west in the course of a few feet. Toward Elsinore mica schist, quartzose, and feldspathic rocks replace the greater portion of the granite. For some distance the schists are cut up by dikes of fine-grained granite, running in different directions, and small bunches of the same rock, often only a few feet across, but sharply differentiated from the schists. Judging from the exposure here, I think we might say that at the time of the metamorphism the action was so intense as to change the sedimentary rocks to mica schists and gneisses and through these to squeeze the liquified portions of the same formation in dikes and fissures. Small fragments of mica schist were noticed in the eruptive masses. In a region like this it is often difficult to draw the line between eruptive and metamorphic rocks. It has been shown before that lamination is no sure indication of sedimentary structure.

Lake Elsinore is bordered on the west by a high and rugged granite range. In the mountains west of Elsinore the granite which cuts off the metamorphic rocks on the Santa Ana range is again replaced by the Metamorphic Series, which are here very greatly altered. They strike a little west of north and dip vertical or at a steep angle to the east. The boundary of the granite is very irregular, and masses outcrop in the metamorphics near the main contact line. Much of this crystalline rock perhaps more truly belongs to the diorites.

The new silver mines lie just north of the San Diego County line, and west of the divide, a position which brings them into Orange County. The formations in which the veins occur vary from a dark brown felsite, often micaceous, to a finely banded quartzose rock. The latter is very compact, and often almost massive. In places hard, blocky argillites appear. The two or more veins found here carry galena bearing silver, and also much magnetite and iron sulphurets, with some of the baser metals. The veins are characterized by a dark red gossan cap on or near the surface. Carbonates are found in this. These deposits exist as impregnations along a fissure, which is not very strongly pronounced. The ore is usually quite massive. The little gangue present is calcite. Not enough development has been made here at the time of my visit to show how extensive the deposits are. The metamorphic rocks extend north along the mountains, forming the summit and eastern slope for a number of miles. Granite borders them on the west toward San Juan. It is probable that this belt of mineral-bearing rocks runs continuously through to Silverado Cañon. At some time this Elsinore basin opened out through the Temescal Valley, but now a low divide separates it from the head of Temescal Creek. Gravel-topped hills lie along the mountains west of the creek. At the terra cotta works a drill was sunk over 600 feet without reaching the bottom of the basin. The Cheney Coal Mine is located 5 miles northwest of Elsinore, in the same basin. The beds dip to the west and southwest, having clay below, and sandstone followed by clay above. The coal is 7 to 8 feet thick, generally solid, but in places showing a parting in the middle. A great deal of faulting has taken place, but there seems to be no system about it. The throw of the faults sometimes amounts to 30 feet, often disturbing the pitch of the vein, and making it greater. The strata evidently belong to the Miocene-Tertiary, for a little farther down the valley fossils of that age are found. This old Tertiary valley, undoubtedly an arm of the sea, opened into the large valleys of San Bernardino and Los Angeles Counties, and extended southerly to Temecula; though south of Elsinore the Tertiary is covered by Quaternary gravels. The depth is unknown, but the width is quite narrow, being from 1 to 2 miles. Not more than a quarter of a mile northeast of the coal mine the metamorphic rocks, quartzites, and hard, blocky argillites outcrop. East of Temescal Creek northward the mountains are formed of a quartz feldspar porphyry of a dark gray color; at times it blends into portions not distinctly porphyritic.

Three miles north of the San Diego County line granite appears again on the east flank of the Santa Ana range and extends north to Cold Water Cañon. Between Temescal Creek and the mountains is a broad, sloping gravel and bowlder deposit of great thickness, resting on the Tertiary. Two miles south of the Temescal Post Office there is an outcrop of soft sandstone carrying Miocene fossils. It dips southwest at an angle of 30°. Extensive clay banks of various colors and nearly horizontally bedded lie along the flanks of the mountains both east and west of the creek. An interesting series of rocks is exposed up Cold Water Cañon. This cañon has been eroded near the northern termination of the granitic portion of the Santa Ana Mountains. The first rock exposed is a micaceous diorite, decomposed to a great depth, but very tough when fresh. This is followed by syenite. A mile up the cañon, near the western edge of this rock and wholly inclosed in it, is a small mass of jasper schist and a lenticular body of semi-crystalline limestone. No traces of fossils were found in it. West of the syenite is another diorite dike. Then follows banded jaspery rocks, sometimes verging on micaceous felsite or quartzites. There are also some slates, and all are often greatly contorted; strike north to northeast. North of the cañon these rocks extend to the summit, while south the Santiago Peak, the highest of the range, and the ridges leading up to it from the east, consist of a coarse quartzose granite, with but little if any triclinic feldspar. A variety of dikes occur near the summit north of the cañon, among them hornblende porphyry, porphyritic granite, and syenite. Fossils were found on the ridge leading up to the summit, north of Cold Water Cañon. They occur in a grayish rock, apparently a fine micaceous felsite. They are poorly preserved, on account of the extreme degree of metamorphism to which the rocks have been subjected. The rocks have become so altered by pressure that they will not break on the lines of bedding, but perpendicular thereto. The fossils consist of impressions of a small bivalve shell. Only about a dozen specimens could be found. The rocks are more altered than any others I have ever seen carrying fossils. These are the first fossils reported from the metamorphic rocks of the Santa Ana range. These fossils when determined will give a clue to the age of the metamorphic gold-bearing rocks of this portion of the State, and also of the granite, concerning which much diversity of opinion has existed.

Dawson Cañon, which heads in the Temescal Mountains, was explored and found to contain interesting geological features. A fine opportunity is given for the study of the relation of the granite to the extensive porphyry intrusives. For 2 miles east of Temescal Creek no eruptives appear; the rocks being wholly of the Metamorphic Series, with exposures of highly altered sandstones, clay shale, conglomerates, etc., striking northwest and dipping southeast at 45° to 50°. About 3 miles up the cañon the argillaceous rocks are replaced by a coarse granite, rich in mica and quartz. This is the prevailing rock up the cañon for 2 miles, and it apparently extends much farther east. It shows a great variation in appearance; much of it contains large crystals of flesh-colored orthoclase. In this granite, particularly on the north side of the cañon, there are dikes of many kinds of rocks. Large dikes of beautiful diorite porphyrites, both light and dark colored, appear in places. At one spot 4 miles from the mouth of the cañon, there are rectilinear dikes of fine-grained granite, intersecting each other like artificial stone fences. For the distance of a mile east, after the granite begins in the cañon, the hills north show nothing but metamorphic schists. The porphyry in the mountains south does not reach the cañon. The great mass of this rock is dark, but in the vicinity of the granite it is lighter colored and more feldspathic, sometimes assuming a granitic structure. In places it is a gray, hard rock, of almost conchoidal fracture, and faint feldspar crystals. The granite near the contact is usually sharply defined, and has a faintly porphyritic appearance at times. The line of junction of the two formations is sharply defined, not only lithologically, but physically. It is difficult to say which is the older. No granite appears in dikes in the porphyry, but there are many dikes of a porphyry-like appearance, resembling the light-colored porphyry in the granite itself. The line of junction is very irregular, and it is certain that the two formations do not belong to the same eruptive mass.

East of the head of Dawson Cañon there is another outcrop of considerable extent of metamorphic rock, micaceous felsites, and other dark schists. A mile west of the Gavilan Mines is a high conical peak formed of coarse, dark diabase. The mines of this district are in white biotite granite, continuous with that of the Pinacate district. The metamorphic rocks south of Dawson Cañon strike east and west, dip north, and extend in a westerly direction nearly to Temescal Post Office. North of the cañon, 2 miles from its mouth, there are a number of outcrops in vein-like forms and in bunches, of a black crystalline material, evidently tourmaline, identical with that at the Temescal Mine. These occur in the metamorphic sandstone and shales. The next large cañon in the Santa Ana range north of Cold Water Cañon shows highly disturbed Tertiary strata at its mouth, dipping away from the range at a high angle. They are soft, white clayey deposits, containing small nodules of selenite. The first of the older rocks exposed in the cañon is a hornblende porphyry, with variations to a granular diorite. For 3 miles up the cañon the only rocks seen are crushed and silicified ones of the Metamorphic Series. They dip, as a usual thing, at a high angle to the east, though in spots it is to the west or horizontal. Quartzose sandstones prevail, with blocky argillitic rocks and conglomerates. Near the summit there are dikes of green tufaceous porphyries.

Temescal Valley is underlaid by clays of a great variety of colors. They are being used very extensively for the coarser kinds of pottery and drain pipe. The Miocene deposits of the valley dip westward from the Temescal range, and instead of also dipping away from the Santa Ana Mountains basin-like, they dip west into the latter range. The dip of these beds 3 miles south of South Riverside is 5° to 10° southwest, and as the Santa Ana Mountains are approached the dip increases, and at a distance of a fourth of a mile, up to the metamorphics, it varies from 45° to vertical. The strata are not exposed all the distance across the valley, but there is no sign of a fold or overthrow; everything seems to point to a gradually increasing dip. This is indicative of an elevation of the region toward Temescal, or a sinking of the Santa Ana Mountains. This is undoubtedly the fault line which follows the range for such a long distance south. Several thin seams of coal outcrop for a distance of 10 miles along the base of the mountains. They have been opened in a number of places and all the strata found dipping into the mountains. The coal seams are often only a few hundred feet away from the metamorphics, and dip toward them at a very regular angle of 45°. Judging from the position of the strata it is not probable that the coal underlies the valley, and as it is so close to the mountains, formed wholly of rocks of the Metamorphic Series, it cannot be of great extent. I believe that appearances point to the whole of the coal beds having been eroded, save the limited, steeply inclined portion at the foot of the mountains. A crowding of the strata against the mountains during the movements along the fault line, have given rise to the steep dip. The highest portion of the Tertiary beds has an elevation of 1,500 feet. A very even, gently sloping plain extends from this elevation toward South Riverside. It is formed of unconsolidated wash from the mountains, deposited on and dipping in the opposite direction from the Tertiary. The Tertiary formation consists of clays in various conditions of consolidation, others chalky in appearance, and a great thickness of argillaceous quartz-sand loosely cemented. Poorly preserved fossils are found in places. Near the southeastern corner of Mr. Hoag’s ranch is a hill with hardened concretionary sandstone outcropping around it. Nearly every portion of this contains fragments of bones supposed to be cetacean. Artesian wells are obtained near Temescal Post Office at a depth of 300 feet. The water is abundant and of excellent quality, and is flumed to South Riverside.

Bunches of granite outcrop in the metamorphic rocks along the east side of Temescal Creek north of Dawson Cañon. At the dam of the San Jacinto Company there is a large outcrop of the beautiful diorite porphyrite, similar to that seen in Dawson Cañon. This extends northwesterly along Temescal Creek toward South Riverside, where it is quarried. It makes an excellent and durable building stone, being compact and free from much mica or hornblende. West of this is a narrow strip of coarse granite, followed by diabase. North of Mr. Hoag’s ranch, and west of the dam, is a dike of black porphyry. Westward the crystalline rocks are overlaid by the Tertiary.

The dam commenced across the Temescal Creek at this point, where it enters the cañon, was intended to have been extended down to the bedrock, and thus bring to the surface the water which flowed beneath the surface channel. The diorite porphyrite is followed on the east by black porphyry.

_Geology of the Temescal Tin District._—The Temescal Tin Mine is located in the northern part of the San Jacinto grant, and about 5 miles southeast of South Riverside. This portion of the grant consists of rolling hills. On the west is a large body of porphyry, extending nearly to the Temescal Creek.

The first rock exposed along the road to the mine east of the creek is a dark flinty one. This is followed by a body of black porphyry, with white feldspar crystals. The porphyry is about a mile across, and is followed on the east by massive black crystalline rock, and that by a felsite. These rocks are soon replaced by granite, in which there are dikes of fine-grained, highly quartzose granite. Little black veinlets of tourmaline aggregates are very numerous in the granite, extending through all the rock up to the porphyry. They have a northeast direction. The material forming them is the same as the gangue of the tin veins. A half mile south of the road is a cañon. Here the porphyry is seen extending up to the granite. The granite is greatly broken near the contact, and though there is no blending of one into the other, there is a confused mixture of broken portions of both rocks. Bunches and dike-like bodies of granite are inclosed in the porphyry. The little veinlets of tourmaline seem to have replaced the feldspar and mica, leaving the quartz. These veins grow larger toward Cajalco Hill. Just west of the works is a great mass of the black veinstone, the gangue of the tin ore. This rises in high, rugged croppings, and covers an area of about 300 by 250 feet. This is the greatest body of vein matter to be seen in the district. The tin deposit worked lies in an eastern prolongation of this cropping. The course of the veins is north 45° east, dip 65° to 70° northwest. The country rock is a coarse hornblendic biotite granite. The vein has the usual character of mineral deposits, swelling at times to a width of 8 feet, and then contracting to much less. The highest grade ore is found in the narrower portions, where it is sometimes almost pure tin oxide, running as high as 70 per cent. The vein matter does not consist wholly of tourmaline, but contains quartz grains scattered through it in about the same proportion as in the granite. The tin is not found in the quartzose part of the gangue to any extent, but in the irregular vein-like deposits of pure tourmaline, which lie in the quartzose gangue. The tin occurs in this in bunches and stringers of nearly pure ore, or disseminated through it. This is particularly the case where the width of the vein is 6 to 8 feet. Where it pinches, the whole vein is sometimes formed of the tourmaline aggregate and tin ore. The vein has usually clay seams on both walls; sometimes it is frozen to one wall; wherever the walls come together and cut out the vein matter, the seams remain. The tourmaline vein matter is an aggregate of needle-like crystals. There are two varieties of tin ore: the yellow, appearing in thin layers in an uncrystalline form; the brown, in granular form in the massive specimens, or in small, clear, reddish brown crystals lining cavities. In the latter case it forms handsome specimens. A small amount of arsenical pyrites is present in places in the vein, and iron pyrites in the granite. The quartzose portion of the vein matter often blends into the granite walls, and there are bodies of evidently granitic origin wholly inclosed in the vein matter. A careful study of the vein matter, and its relation to the walls, shows that it is simply a portion of the granite, in which the feldspar and dark silicates, hornblende, and mica have been removed and tourmaline substituted. The quartz has the same character and color as that in the granite, and many transition stages in the process are shown. Where the action has been more intense, near and along the fissures, the quartz has been wholly removed and the tourmaline deposited, together with the tin. Cajalco was the center of this action. The veins decrease in size farther away.

At the time of my visit the mine had been opened to a depth of 180 feet, by two working shafts. The total length opened on the vein is 300 feet. Two levels have been run and work was in progress on the third. The main ore body lies in the center of the workings, and extends downward in the dip of the veins. The ore milled averaged 5 per cent of tin oxide, though large portions, as before stated, are very high grade. The company has also prospected Cajalco Hill by tunnel and open cuts, and one or more of the veins south by shafts. At the time of my visit two of Husband’s pneumatic stamps were in operation. They weigh 900 pounds each, and drop one hundred and thirty-five times per minute.

South and southeast of the works are many bunchy veins of the black tin gangue. They often carry considerable iron. They extend, generally nearly parallel, in a northeast and southwest direction. Some appear as mere bunches on the surface. These veins closely resemble the main vein at Cajalco Hill, and are due to the same action, and it has been supposed that many of them will be found to carry tin, though it is not present on the surface. About 2 miles south the granite is replaced by a banded feldspar porphyry. This cuts off the tourmaline veins. The granite about the works, and especially toward the contact with the porphyry, is cut by many dikes of a fine-grained granite, having an excess of quartz and feldspar. Associated with the porphyry are strata of metamorphic rocks, of a hard, dark, quartzose character. A quarter of a mile northwest of the mine is a bunch-like outcrop of porphyry, carrying silver and copper carbonate. The black veins outcrop for a distance of 2 miles northwest from the mine, extending into the porphyry, which replaces the granite in that direction. The granite extends eastward for many miles.

The general geological features which obtain here are: A semi-circular area of granite over 2 miles in diameter, surrounded on the northwest and south by porphyries and joined on the east to a great body of granitic rocks extending indefinitely in that direction. Around the border of this granite protuberance are many dikes of a fine-grained granite. Cutting through the granite in a northeast and southwest direction are the black tourmaline veins, which form the gangue of the tin ore when it is present.

Tin occurs here under conditions different from any other known deposit. Tin veins are almost always found in granitic formations, but such an extensively developed tourmaline veinstone is remarkable. The direction of the fissure system shown here is an uncommon one in California. The veinstone, together with the associated metals, has probably resulted from a process of sublimation along lines of fracture, removing those portions of the granite easily affected, over a large area, as at Cajalco Hill, and in the immediate contact completely replacing it with the massive aggregate of minute tourmaline crystals.

Thanks are due to the manager, Captain Harris, for the facility freely afforded me for examining the mine, the works, and the country about.

North of South Riverside the Tertiary beds dip at a small angle to the north. The Santa Ana River has cut its course through the hills at the northern end of the Santa Ana Mountains. No outcrop of the metamorphic rocks appears in the cañon. The Tertiary strata no longer dip toward the west, but in the Chino hills north of the river show a great anticlinal arch. Along the south side of the river the beds dip 70° northeast; farther west, near the heart of the range, they dip 60° southwest, strike north 30° west. Near the upper end of the cañon there are fault lines dipping toward the range, which show an elevation of the hanging wall. Bedrock Cañon is the first large one which opens to the Santa Ana River from the western slope of the mountains. Opposite the mouth of this cañon the greatest amount of water appears in the bed of the river, indicating the presence of hard rock only a little distance below. Coal veins are located near the head of this cañon, one 700, the other one 1,300 feet above the river. They dip only a few degrees to the southwest. They are exposed on cliffs facing the mountains to the northeast. Below them are very hard sandstones carrying fossils, probably Cretaceous. One prospect shows a number of seams within a width of 8 feet. The widest is 29 inches, the others much smaller. The other prospects show only one 39-inch seam. Their position, lying so flat high on the mountains, indicates an uplift without great disturbance, while the gypsum mines farther down on the flank of the mountains dip at a high angle to the southeast. It may be that all of the coal deposits of the western slope of the Santa Ana Mountains belong to the Cretaceous, and have been greatly separated by faulting and folding. A deposit of white, granular gypsum has been opened in Gypsum Cañon, 2 miles south of the river. The beds have a thickness of 8 or 10 feet. At one spot a large mass of crystalline dolomite was found. The deposits run with the strata, north and south, and dip west 60°. As we approach Olive, the few croppings seen still dip south or southwest, but at a less angle. South of the mouth of Silverado Cañon a line of hills extends north and south, bordering the Santa Ana Plain. The western portion of these hills is formed of basalt considerably decomposed. The basalt varies from scoriaceous to fine-grained and compact. Its eastern edge was seen to rest on Miocene sandstones, and it dips west at a small angle, perhaps 10°. The lava seems to have been squeezed up in fissures, judging from the way in which it outcrops. Its greatest elevation is 800 feet. At some places the sandstones, where not covered with lava, have been silicified, turned to quartzite, or rendered granitic in appearance. This may be due to an intrusive neck of lava, or more probably to the action of thermal springs.

An interesting fold of the Tertiary strata was observed at the entrance of Santiago Cañon. The sandstones and conglomerates on the eastern side dip to the northeast at an angle of 30°, while those on the west side dip in the opposite direction. The valley has been eroded in the summit of an anticlinal. The rocks of the eastern side rise again against the side of the mountains, thus forming a synclinal. Up the cañon the sandstones on the west maintain a southwest dip of 45° to 50°, and strike north 40° west. The cañon finally leaves the anticlinal, and the rocks dip southwest on both sides. Toward the summit of the hill, north of the Harris Coal Mine, the dip increases to 70°, but on the top they turn so that the strata lie horizontal. Here they consist of clay shale. The strata at the coal mine swing around, and one mile northeast they strike north and south and dip west. This hill seems to form the southern termination of the anticlinal ridge north of Santiago Cañon. Southeast of this point there is a simple monoclinal fold or slope away from the older rocks of the high mountains. There has apparently been a fault extending northwest in this anticlinal ridge, bringing up the clay shales which farther south were shown to belong to the Cretaceous. Harris Coal Mine shows a seam 18 inches wide, shale forming the foot wall and sandstone the upper. There is a fault of 200 feet cutting this coal seam. The sandstone at the mouth of Silverado Cañon dips south 30°, forming bold cliffs. A half mile up the cañon there are heavy beds of clay shale inclosed in the sandstone. Cretaceous fossils appear in the shales, as well as in a coarse sandstone which underlies them. This sandstone is replaced by conglomerates near the contact with the underlying Metamorphic Series. The sandstone rises to a height of 2,500 feet, with bold, almost perpendicular cliffs facing the mountains. Portions of the sandstone containing the fossils are often very much hardened.

The first crystalline rocks met are dark and fine grained, with traces of bowlder-like inclusions, and are evidently eruptive tuffs. Above these are green, dioritic rocks. These intrusives are followed for several miles by sandstone and shale, in which the stratification is often obliterated. In other places thin layers of sandstone and shale are wonderfully contorted. The dip is at a high angle either east or west. In the vicinity of the old Silverado Camp there are dikes and bunches of a green dioritic rock. The mines in the Silverado district are again being developed to some extent. The mineral belt is about 2 miles wide, and extends nearly north and south. The country is formed to a great extent of dikes of greenish to blackish rocks, often showing distinct hornblende crystals. The dip of the metamorphic rocks is east about 45°. There is one main mineral vein located, beginning about a mile north of Silverado, and extending in a southerly direction for 7 or 8 miles. The Quincy Mine is one of the most northern ones. The vein has a width of 2 feet; the ore, silver-bearing galena in a calcite gangue. It carries but little base metal of any kind. The ore has a peculiar appearance, the galena being distributed through the gangue in little leafy crystals or aggregates. The fissure is well defined and regular, with a pale green syenitic rock on the hanging wall, and a dark diorite on the foot wall. This hanging wall rock weathers to a light gray color, producing a rock known as porphyry among the miners. South of this mine a side vein carries much antimony. The Quincy has been opened along a length of 500 feet. The ore is quite uniform, producing one eighth in concentrates. The Quincy camp has an elevation of 2,300 feet. South of Silverado Cañon, in Silver and Pine Cañons, a great amount of work was done during the former excitement. The sides of the steep, rocky cañons are fairly honey-combed with tunnels, which were undertaken without sufficient prospecting, and, of course, never struck anything. The New York Mine spent much money, but did not prove a success. West is the Princess, and farther still, about 1,200 feet above the cañon, is the Blue Light Mine, on which much work has been done and rich ore taken out. The mines south of the cañon are in a feldspathic rock, which weathers white. It is undoubtedly an intrusive porphyry, for traces of feldspar crystals are to be seen. The mines are characterized by a large amount of zinc-blende, iron pyrites, and not a large percentage of lead, making them more difficult to reduce. The porphyry is mineralized in many places where no traces of the precious metals occur. Litigation and poor management seem to be the chief factors in stopping work in this district. Though some of the ore runs into hundreds of dollars to the ton, the most of it is medium to low grade.

About a mile and a half down the cañon from the old Silver Post Office, and in a cañon coming in from the south, is a cropping of dark, somewhat argillaceous limestone inclosed in shales. The limestone does not seem to have been highly metamorphosed, yet the fossils which it contains are almost obliterated. The faint impressions are those of coral stems, stromatopora, and some other low forms of life. Half a mile farther down the cañon is a cropping of brecciated marble. At many points, particularly on the north side of the cañon, there are great masses of apparently conglomeritic character, but with a crystalline structure. The matrix has a green to brown color, and in it are imbedded pebbles of the same degree of fineness, but often distinguished by much brighter red, purple, and green colors. In this cañon, as in others of this range, the water holds much lime in solution, and extensive tufas are frequently to be seen. The basal members of the Cretaceous at the mouth of Silverado Cañon consist of conglomerates passing up into sandstone, and those into shales; dip 55° away from the mountains in the highest ridge, but in the course of a quarter of a mile becoming much less. The change in dip is very sharp, giving the appearance of a fault.

A cañon which enters Silverado Cañon from the northeast near its mouth was followed up nearly to its head for the purpose of investigating some limestone outcrops. The first outcrop in this cañon is the usual dark porphyry. Beyond this the stream has cut a deep cañon through an immense conglomerate of porphyritic and quartzose pebbles. The porphyritic pebbles are dioritic and part red and black porphyries. Some of them are similar to dikes farther up the mountains. Through this great conglomerate bed there are dikes of black porphyry, with pale feldspar. Tufaceous porphyries form a large part of these dikes. The base is purple and the pebbles light green, or the reverse. These conglomeritic porphyries differ from the great beds of sedimentary origin, in having all the pebbles of a uniform character with a crystalline matrix. The sedimentary beds contain pebbles of all sizes and description, in a matrix of small pebbles or coarse sand. Farther up the cañon the great body of the rock is crushed shale and black to gray sandstone; dip vertical, inclining most generally to the east, strike north and south. Two miles up the cañon is a dike of diorite porphyrite, coarse in the middle and fine on the edges. Four miles up is a stratum of gray limestone. More outcrops appear on the north side of the cañon, but whether they belong to the same stratum or different cannot be told, on account of the crushing undergone. These deposits are bunchy, swelling in one case to a width of 100 feet. It is not crystalline. The color is from black to gray. It contains fine specimens of a bivalve shell, and faint traces of corals and univalve shells. These beds are said to extend to the summit, and undoubtedly further examination would reveal more fossils. Several specimens were sent to the National Museum and pronounced Carboniferous in age. We have here, then, the first announcement of the age of the Santa Ana range. This range stands in such intimate relation to the granite and crystalline schists farther south, that an approximate determination of the latter is made possible. Professor Whitney and others following him have classified this range as Cretaceous. Their grounds are utterly untenable stratigraphically, but this discovery of Carboniferous fossils makes the evidence of greater age certain.

On the eastern side of the range, near its northern end, the sandstones were observed to be silicified, being filled with a network of quartz veinlets, exactly similar to the silicification of the metamorphic rocks of the Coast Range proper.