140 
GEOLOGY. 
and is indicated by the islands of Anacapa, Santa Rosa, Santa Cruz, and San Miguel. It is 
nearly parallel with the Bernardino Sierra, and holds a relation to that chain similar to that of 
the Coast Mountains to the Sierra Nevada. If the whole region, with the bed of the ocean, 
were lifted up, so as to drain the valley now occupied by the channel of Santa Barbara, a valley 
would be formed similar in many respects to that between the Sierra and the Coast Mountains. 
With regard to the general or average elevation of the Coast Mountains we are without 
sufficient data to form an accurate conclusion. Several determinations of altitude have been 
made in the vicinity of San Francisco, but the observations along the ranges south of that point 
are very few. Table Hill, north of the entrance to the bay, is 2,569 feet high, and there are 
many higher summits beyond. South of the entrance, the San Francisco or San Bruno range 
commences in hills of moderate elevation, but increases in altitude towards the south, until 
opposite the valley of San Jose the average elevation of the range is not less than 2,000 feet. 
There are many lofty ridges between San Jose and Santa Cruz. 
Blue Mountain, a few miles southwest of the city, is 1,097 feet high, and another point a little 
farther south is 1,263. The Contra Costa range, opposite San Francisco, probably has the 
average elevation of 1,800 or 2,000 feet. One of the summits, nearly opposite the entrance of 
the bay, is reported to be 1,952 feet high. 1 This range forms the highlands on the east side of 
the bay, but does not rise abruptly from the shore, being flanked by a margin or gentle slope 
of alluvial origin, upon which the villages of Oakland, San Antonio, and Clifton are built. 
Further south, it is much broader and more valuable for agriculture. 
The third, or Diablo range, extends southeasterly from Mount Diablo, bordering the broad 
valley of the San Joaquin. It is separated from the Central range by a long valley—a part of 
which is known as Livermore’s ; but nearly opposite the south end of the Bay of San Francisco 
the two ranges appear to unite in one. The average elevation of a part of this range is not so 
great as the Contra Costa or San Francisco range. It is composed of a series of hills with 
rounded outlines and a moderate elevation ; but at the northern extremity, Mount Diablo rises 
with a bold and rugged outline to an altitude of 3,960 feet. 2 It is a majestic mountain and a 
prominent landmark, being visible from distant points in the Sacramento and San Joaquin 
valley, and from the ocean when approaching the entrance to the bay. It is also distinctly 
visible from the city of San Francisco, rising high above the crest of the Central or Contra Costa 
range. The low hills, which constitute a part of the range, bound Livermore’s valley on the 
east, and are broken by several passes—one of which (Livermore’s) was surveyed by the Expe¬ 
dition, and found to have an altitude of 686 feet. 
The southerly prolongation of this range—beyond the point of unison with the Contra Costa 
or Central range—reaches a greater altitude, and is marked by several prominent peaks which 
have not been fully explored. Pacheco’s peak, which is nearly opposite the headwaters of the 
San Joaquin, is reported to be 2,700 feet in elevation, and to be composed of volcanic rocks. 3 
The entrance to the Bay of San Francisco—the Golden Gate—together with the channel 
reaching to the valley of the Sacramento and San Joaquin, is one of the most remarkable 
breaks in a chain of mountains which is yet known. It is like a great cleft or fissure, and 
extends at right angles to the trends of the ranges. The ridges end abruptly on each side of 
the Golden Gate. Those on the north side, being undermined by the currents, present bold, 
vertical cliffs of rock, and thus increase the resemblance to a great cleft. The shores of the 
1 For these altitudes see charts of the Bay of San Francisco, by Cadwalader Bingold, commander U. S. navy, 1850. 
2 Report of Lieut. R. S. Williamson.— (Senate, 31st Cong., 1st sess., Ex. Doc. 47, p. 35.) 
3 J. B. Trask—verbal communication. 
