The region, although entirely eruptive, and in part volcanic (large fields of basalt occurring on the western slopes) is in the immediate vicinity of a large hill called Pinto, or Painted Mountain, which is made up of metamorphic strata, chloritic and hornblende rocks, quartzite and mica schist predominating. The mineral-bearing veins of the Monte Negras District are all of the fissure type, and are mostly quite simple in form. The gangue is quartz, carrying iron and copper sulphurets, and the secondary products of those minerals, iron oxide and copper carbonate, with gold and silver. No lead or zinc was observed. The economic value of the ore lies almost, evidently, in its gold contents, the silver occurring so sparingly as to amount to very little. The bullion obtained from these ores is worth about $17 per ounce. The ore ranges in value from $20 to over $100 per ton. Observations on the principal mines of this district, viz.: Great Eastern, Venus, Columbus, Summit, Porcupine, Schiller, Hillerman, Annie Rooney, Ethel, Republican, Ramona, McKinley Bill, and Revenue, have to be omitted in order to condense the report. SAN DIEGO COUNTY. By W. H. Storms, Assistant in the Field. There has been no marked development of mines in this county since the last report was issued, excepting in some of the districts of the Colorado Desert, of which mention will be made. The general geological and topographical features of this county have been so fully described in former reports that to repeat them here is unnecessary. At various times within the past two years new discoveries have been announced, and these have been developed to a greater or less extent, and in some instances, at least, with encouraging results. HELVETIA MINE. This mine is located a short distance from the town of Julian, and is equipped with a steam hoist and mill combined under one roof. The new shaft, which was started nearly three years ago, was sunk on the vein for 50 feet, at an angle of 75°, at which depth the shaft left the crevice and continued vertically to a depth of 225 feet. From this point a crosscut was started back toward the vein, running at an angle with its strike, the idea being to reach a pay shoot as quickly as possible. The shoot in question was the south extension of that developed in the old workings. The vein was encountered, and the drift continued along its course. At about 30 feet from the point of intersecting the vein in this drift of the shoot was found. It was hard, blue, rather glassy-looking quartz, filled with minute black particles, and showing considerable gold, some of the rock being very high grade.