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,