Excerpts from Cronise, Titus Fey, The Natural Wealth of California (1868) [PP. 156-7:]

The climate of this county, influenced by the position and height of its mountains, is subject to great variations. Monte Diablo, a prominent landmark in this part of the State, 3,381 feet high, is the principal agent in producing these atmospheric changes. This mountain is supposed to have been at one time a volcano, a presumption strengthened by the double cone forming its summit when viewed from the east, caused by the breaking away of the rim of its crater on that side. It is situated in the northern part of the county, and has a length of eight or ten by a breadth of five or six miles. It is somewhat crescent-shaped, the concavity opening to the northeast, and forms a barrier to the winds coming from both the interior and the sea, which sometimes blow with great violence about its base, while the atmosphere higher up its sides is but little disturbed and even quite calm at its summit. It is a grand and singular sight to see from its top, where all is clear and tranquil, the clouds rolling in stormy commotion far below. These atmospheric phenomena are most strikingly manifested after mid-day, in the fall of the year. For several hours in the afternoon, the dry and heated air from the interior sweeps up the mountain with a strong current. About three o'clock the moist air from the ocean begins to reach it, and the two currents meeting, form fleecy clouds which hang around its base and fill its lower valleys, condensing, as the night comes on, into heavy and refreshing dews.

[P. 161:] Silver-bearing ores have been found at various places about Monte Diablo. Sixty pounds of ore, taken from a claim known as the Open Sesame, in 1863, yielded, by working process, at the rate of $48 33 per ton in gold, and $243 per ton in silver, while the San Pedro ledge yielded ore that assayed at the rate of $40 per ton. The broken stratification in this district, however, has thus far rendered all attempts at working these claims abortive. During 1862, and the following two years, some fifty cupriferous deposits were partially explored in the vicinity of Monte Diablo, and, although a considerable quantity of ore was obtained from them, it was of too low a grade, and the seams were too much broken up, to warrant a continuance of operations.

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