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.