The lowest Cretaceous beds are between Silverado and Williams Cañons, but the fossils are very similar to those generally found through the Cretaceous of this region. The lowest beds are a duplicate of those seen at the mouth of the Silverado Cañon, though apparently a thousand feet lower in the series. Between the two beds there is another conglomerate stratum, carrying bowlders different from any seen in the Santa Ana Mountains. Many of the porphyry bowlders in the basal Cretaceous conglomerates resemble the porphyry about Temescal. The Santa Clara Coal Mine, at the mouth of Silverado Cañon, is undoubtedly in strata of Cretaceous age, though no fossils are found in the strata above till the Miocene is reached. Up the Santiago Cañon as far as Madame Modjeska’s place, the fossils are chiefly confined to the eastern side of the cañon, but the character, dip, and strike of the strata on both sides are the same. The Cretaceous is separated from the metamorphics by a line of cross cañons. The highest portions of the Cretaceous terminate in a line of hills with sharp eastern escarpments.
Shrewsbury Cañon comes in just below Modjeska’s. After passing the Cretaceous, through which the cañon has cut, the Metamorphic Series was seen to consist of slates and sandstones, followed by light-colored granitic rocks, chiefly hornblende and triclinic feldspar. The metamorphic rocks generally dip to the east.
A mile above Modjeska’s the Santiago Cañon cuts through bold cliffs of Cretaceous sandstones and conglomerates, and higher up still has eroded a cañon in the Metamorphic Series. The cliffs, a little back from the stream, rise probably 1,000 feet. Sandstone belonging to the Metamorphic Series outcrops in the cañon for some distance, and is followed by conglomeritic porphyries, containing purple and red bowlders. In some places the inclusions are angular. These rocks are extensively developed about the Santiago Mines and higher up in the mountains.
Just below the Alma Mine, on its western side, the creek has cut through dikes of diorite, which are coarse in the center and fine on the edges. On the hill south of the Alma Mine the diorite is on the opposite or eastern side of the vein. Although the exposures are poor, all the crystalline rocks have the character of intrusives. No blending into the metamorphic rocks has been noticed. About 3 miles up Shrewsbury Cañon several claims are located on the southern continuation of the veins of the Silverado district. Near the head of Santiago Cañon these again appear well defined, and considerable active work was going on here at the time of my visit. The veins here have a direction a little east of south, dipping to the east somewhat less than 45°. It appears that the mineral belt follows a certain line, generally quite regular, without any particular reference to the dikes and bunches of intrusives scattered irregularly here and there. The fissure system has taken a comparatively regular line and the walls may or may not be intrusive. The Alma Mine, the northern claim of the Santiago Silver Mining Company, has been worked by the former operators in a very irregular manner. The veins and stringers as far as exposed lie wholly in the crushed quartzose argillites. 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. South, on the hill, the Morrow claims have been bonded by the same company and are being opened. On the summit of the hill diorite lies on the eastern side of the veins. Down the southern slope the veins lie wholly in metamorphic rocks; the foot wall being more silicious, the hanging argillaceous. The mineralized portion has a width of 20 feet. A small vein occurs in the upper side, and a heavier one, sometimes reaching 3 feet, on the foot wall. There are occasional stringers in the crushed portions between. The gangue is calcite, with some quartz, all mixed with the broken clayey slates. More zinc-blende and iron pyrites are found here, also a little antimony. In the Alma Mine the richest galena is very fine, and sometimes resembles antimonial ores.
South of these mines, toward Trabuco Cañon, another claim is being worked. South of the Trabuco the conglomerates hide the lode, except at one spot, where it appears and has been worked. The Cretaceous formation grows lower as the Trabuco is approached, and does not appear prominent south of it. In all probability it is covered by the Tertiary, for the elevation and consequent erosion have not been as great in this direction.
SAN BERNARDINO COUNTY.
By W. H. Storms, Assistant in the Field.
No portion of California has more diversified mineral wealth than the county of San Bernardino. Although its area is comprised largely of rugged mountains and desert waste, yet this county is a producer of gold, silver, copper, lead, and tin, and contains mines of zinc, iron, and manganese, besides deposits of borax, salt, soda, baryta, gypsum, sulphur, onyx, marble, asbestos, and structural material, granite, and sandstone of great beauty and value. Within its borders are found a wide range of geological formations from Paleozoic (if not Archæan) to Tertiary, and a great variety of rocks of igneous origin.
The mines are scattered all over its thousands of square miles of territory, and have already added millions of dollars to the wealth of the State and the world. Many of its mines are of phenomenal richness, and were it not for the expense and extreme difficulty attending transportation in the desert, San Bernardino County would undoubtedly take first place in adding to the mineral wealth of California. The largest and most productive section in the county at present is