Harold W. Fairbanks

“ The Monte Negras uplift consists, as far as my observation extended, entirely of eruptive rocks, diorite, quartz porphyry, and fine-grained more or less porphyritic rocks, cut by later dikes of felsite and dark-green or black diorite. Epidote occurs in great quantity throughout the region, usually associated with micaceous iron ore, which is found in the form of veins and bunches everywhere. The iron ores contain no precious metals, and are of no economic importance. ”

“ 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. ”

“ The sandstone shows somewhat less metamorphism toward the north, where it contains some strata of pebbly conglomerate. The granite is intersected by many veins of coarsely crystallized feldspar and quartz. From these veins many of the pebbles in the conglomerate have been derived. At the highest point of the ridge the sandstone has the greatest thickness. Here it is broken up into great blocks 15 feet square, piled in the greatest confusion, as if by an earthquake. One great mass overhangs the almost precipitous granite escarpment at an elevation of 1,000 feet above the desert. ”

“ With the uplift, the strata inclosing the borax mine were tilted and folded, and now the sheet of white calcium borate which once lay glistening in the sun on the bed of a desert dry lake stands like a great vein 60 traversing the country. There are apparently two of these veins in close proximity to each other, but I believe them to be one and the same, being repeated as the result of an anticlinal fold. An ideal cross-section of the borax mine is here given (p. 347) , showing the nature of the folding at that point; it is not drawn to a scale, being a sketch only. ”

“ The largest shoot of ore I saw has formed very close to the point of intersection of the felsitic dike with the main vein. On the Desert Queen a long tunnel and several crosscuts have exposed ore bodies, some of which contained upwards of 200 ounces silver per ton.
The Imperial lode is one of the most promising veins of which I have any knowledge, but it requires considerable capital to properly and systematically open it. The rock is extremely hard, and the lack of wood and water are drawbacks which prevent the owners from working the mine as it should be worked. ”

“ 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. ”

“ Though the original condition of the ore was doubtless sulphide, it now contains, as the result of oxidation, hematite, limonite, magnetite, malachite, azurite, chrysocolla, cerussite, wulfenite, chloride of silver, manganese oxide, and metallic gold. The value of the ore lies principally in the gold contained, though in one portion of the ore body, near its eastern end, rich chloride of silver ore is found, with but little gold. The physical appearance of the ore is no criterion of its gold contents, as two pieces, with identically the same characteristics, will differ widely in value. ”

“ 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. ”

“ 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. ”

“ 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. ”

“ A pretty valley, a mile long, has been eroded in the eastern end of the gravels, down to the underlying granite. Placer mining has been carried on for years here in a small way by Mexicans. Gold is said to be scattered everywhere through the gravels, which are often very firmly cemented. Lack of water, for the ridge is higher than any of the surrounding country, has prevented work on a large scale. Lately a mining district has been organized, and it is proposed to bring water 7 miles in pipe. In the gravels are washed bowlders, many of them being 2 feet in diameter and well polished. ”

“ The crystalline rocks exposed between the Sweetwater and El Cajon Valley generally show more of a dioritic composition than granitic. 18 They have a glassy feldspar, much hornblende, and little quartz. There are two varieties: one is light colored, and forms most of the country; the other is darker, occurring in bunches and dikes. Southwest of the valley the rocks are more granitic. On the road to Spring Valley they give place to a hard, light—colored felsitic rock, containing specks of chloritic matter. Masses of granite appear in places, intruded into the rock. ”

“ 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. ”

“ The most abundant is a red feldspar quartz porphyry. Quartzite bowlders of all colors are numerous, and there are a few of the basic diorite so common in portions of the county. Garnets are said to be very abundant in the gravels, and many bowlders of a schist carrying them are also present. The matrix of this rock could not be made out in the field; it is very tough and heavy, and has never been seen in place. The red porphyry bowlders resemble those on the mesa farther west, but have never been found in place. ”

“ Black tourmaline in a feldspathic and quartz gangue frequently accompanies the gold-bearing rock. The Mexicans worked a large shoot down to the water-line, and judging from the size and number of the dumps these old workings must have been of great extent. The Riverside people had sunk a new shaft at the extreme south end of the mine 180 feet in depth. The entire region is cut by large feldspathic and granitic veins, which course in every direction. These veins are doubtless intrusive dikes of the variety of granite called pegmatite. ”

“ About Fallbrook, and for some distance east, the granite does not outcrop much, owing to its easy decomposition. A little east of De Luz Station is a small body of mica schist; dip 30° east, strike north 15° west.
The road from Fallbrook to Temecula leads through a long, narrow valley. On either hand rise high mountains of bare granite. Immense bowlders, 20 to 30 feet across, line the valley, having fallen from the cliffs. The granite here is a coarse rock, rich in biotite, and though great masses could be obtained free from checks, yet does not seem durable. ”

“ A tunnel is now being run to open what is supposed to be the main vein, several hundred feet farther east, and which has syenite on the hanging wall. Other tunnels are being run along the creek, one near a body of granitoid rocks, others in slate or quartzite. The ore is a leafy galena, arranged often in narrow bands with the crystalline orientation different in alternating bands. Sometimes it occurs in the form of large solid bunches. Thus far the ore deposits have been found quite irregular, but it is thought that the main body has not yet been reached. Very little base metal is present. ”

“ The ore deposits are usually discovered by the cherty masses of silicious rock, which, being harder than the limestone, stand out from its weathered surface in bunches and small, vein-like masses. Often in 77 breaking the cherty rocks, stains of copper carbonate are found, and from such rock silver, and sometimes gold, is obtained. Numerous shafts, cuts, and tunnels have been made on these claims, twenty or more in number, and in every one ore of good grade has been found, although the quantity is usually small. ”

“ The sandstone underneath the high plateau is higher than the divide at that spot, and the only granite within miles that exceeds it in height, is the narrow ridge which rises on the southeast. The erosion must have been very great along the ridges since the sandstones were deposited, but the valley cannot have changed much. There may have been great elevation along the crest of the range bordering the desert since the deposition of sandstone, tilting up the sandstone and lava on the eastern slope, but elevating without great disturbance those near the summit. ”

“ At the foot of the mountain there is a small outcrop of ancient volcanic rock greatly altered. This rock rests against the limestone which forms a large part of the north end of the mountain. The limestone is crystalline in every portion. The strike, as well as that of the schists and quartzites by which it is inclosed, is north 30° to 40° west, dip 75° to the southwest. The color of the limestone varies from white to streaked and variegated. It was carefully examined for fossils, but no traces of them could be found. ”

“ The formation in which the Coyote vein has formed is micaceous and hornblende schist and gneissoid rock; hornblende granite and dikes of diorite also occur 91 in the vicinity of the vein. The Coyote Mine is a quartz vein from 2 to 4 feet in width. The rock is iron stained and occasionally shows free gold. The vein is developed by two shafts, one about 20 and the other nearly 80 feet in depth, and strikes 5° north of east, having a dip of 46° to the south. The vein appeared to cut the formation at a small angle. ”

“ The fresh massive central portion weathers out like water-worn bowlders. The presence of rugged angular ridges results either from a less inherent tendency to decay, or to a comparative freedom from crushing. Four miles northeast of Campo is an outcrop of coarse hornblendic granite, with large six-sided mica scales and numerous yellow crystals of titanite. The height of the divide is 3,800 feet. Near the summit the rocky ridges all disappear and the country becomes covered with granitic sand. Erosion here is evidently very slight. ”

“ 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. ”

“ The strata of the high cliffs north of La Jolla dip northerly at a small angle, and show only a few fossils of the Eocene age. The cliffs rise fully 400 feet. At the bottom of the cliffs are shales; higher up are great beds of conglomerate bowlders, chiefly a reddish porphyry.
Coal is reported to outcrop above the water at very low tide somewhere along this stretch of cliffs. It of course must occur in strata of Tertiary age. The coal vein struck in a boring at La Jolla must be Cretaceous. About 3 miles up the coast from La Jolla, there appears a dike of basalt cutting the Tertiary shales. ”

“ 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. ”

“ The silver frequently is found in the same shoots with the base ores and in quartz without any intimate association with either lead, copper, or iron. The galena is sometimes very low grade, carrying only 4 ounces per ton in silver. In one shoot the lead carbonate contains over 200 ounces. It is a notable fact that no good ore is found in quantity without copper in some form, either as sulphide (glance) or carbonate. Chloride of silver is also found associated with iron and manganese, without copper or lead. ”

“ Nearly all the lenses exhibit a tendency to “make” into the hanging wall side of the country rock, the lenses of quartz following each other in a general direction, but at an angle with the stratification of the schists, and are separate and distinct from each other, being separated at the ends (where they sometimes overlap) by the “leaves,” as 82 they may be termed, of the schistose country rock. These lenses were doubtless caused by a compressive stress on the schists, which had a tendency to split them, but was not powerful enough to cause an abrupt fracture. ”

“ The borax vein is traceable for several thousand feet, striking along the western and northern side of the largest sedimentary hill in the range, and finally passing down a cañon to the eastward, where it becomes a well-defined vein. Toward the western end the borate of lime appears to be much mixed with the sandy sediments, gypsum, and clays, giving the appearance of having been formed near the shore line of the basin in which this great mass of material has been left as a residuary deposit, due to the evaporation of the water containing the calcium borate. ”

“ 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. ”

“ At the east end of the belt is an accumulation of tufa and basalt. The belt dips south at an angle of 75°. The mineralized portion of this lode extends from the porphyry dike east through three full claims, disappearing finally beneath the eruptive rock and desert wash. The dominant point on the lode is 550 feet above the base of the hill.
The entire lode is gold-bearing, some of the iron rock being extremely rich; gold also occurs in the calcite, though it is usually of a lower grade than where accompanied by the iron. ”