valleys, has a northwest-southeast trend. On the southwest it is separated from the Pacific Ocean by the Santa Lucia Range and from Carmel River by the Sierra de Salinas. On the northeast it is separated from the San Joaquin Valley by the Mount Diablo Range and from the San Benito Valley by the Gabilan Range. This region is entirely included in the rectangle bounded by parallels 35° 10′ and 36° 50′ north latitude, and meridian 119° 30′ and 121° 50' west longitude. The Salinas Valley lies entirely within the boundaries of Monterey and San Luis Obispo counties. TOPOGRAPHY. The Coast Range of California southeast of San Francisco consists of a series of parallel mountain ridges extending in a general northwest-southeast direction. This system of ranges has received the general and comprehensive name of Coast Range, but the subordinate ranges have also been designated by local names, some of which are not yet well established. Of these ranges the most northeasterly is the Mount Diablo Range (Pl. I), which as a system of parallel mountain ridges extends from Mount Diablo, in Contra Costa County, to Mount Pinos, in Ventura County, where it merges into the complex mountain region west of Tejon Pass. The length of this range is 270 miles, and for this entire distance it is the barrier between the San Joaquin Valley on the northeast and the Cuyama Valley, the Salinas Valley, and San Francisco Bay, with its adjacent valleys, on the southwest. The highest peaks in the central portion of this range are Santa Ana Peak, altitude, 3,578 feet, and Castle Peak, altitude, 4,347 feet. The average altitude of the crest of the range is not known definitely, but it must be at least 3,000 feet. The Santa Cruz-Gabilan Range (Pl. I) extends, with one break, from the Golden Gate southeastward 120 miles to Chalone Peak, beyond which it ceases to be a prominent topographic feature. Pajaro River breaks through this range, dividing it into the two portions known locally as the Santa Cruz and the Gabilan ranges. In the southern range the highest peaks are Gabilan Peak, altitude 3,100 feet, and Chalone Peak, altitude about 3,000 feet. This portion of the range has an average altitude of about 2,500 feet, and a length of 40 miles. It is the barrier between the lower Salinas Valley on the southwest and the San Benito Valley on the northeast. The Santa Lucia Range rises abruptly from the ocean south of Carmel Bay and extends southeastward along the coast as an unbroken chain to Cuesta Pass, in San Luis Obispo County, a distance of 100 miles. The seaward slope of this range is exceedingly precipitous, and is scored by deep rugged canyons, down which small torrential streams find their way to the ocean. The average width of this slope in Monterey County is about 5 miles. At one place it is but 3 miles from the crest of the range to the ocean, and the greatest width is but 9 miles. The highest peaks in this range are Santa Lucia, altitude 5,967 feet; Boulder Peak, altitude 4,417 feet; Pico Blanco, altitude 3,680 feet; Roundtree Hill, altitude 4,300 feet, and Pine Mountain, altitude 3,600 feet. The average altitude of the crest can not be less than 3,500 feet, and is probably nearer 4,000 feet. Between the Salinas Valley and the high Santa Lucia Range are other mountain ranges, the most northern of which is known as the Sierra de Salinas (Pl. I). This is a long mountain ridge extending from the mouth of the canyon of Arroyo Seco, in Monterey County, northwestward about 25 miles to the mesa lands lying southwest of Salinas. It presents steep slopes toward the Salinas Valley, shutting out from view the higher and more rugged ranges nearer the coast. The highest point, Mount Toro, altitude 3,553 feet, is a broad, rounded ridge. This range probably has an average altitude of nearly 2,500 feet throughout its entire length. The mountain range known as the San Antonio Hills (Pl. I) is a divergent ridge sent off from the most elevated portion of the Santa Lucia Range. It terminates rather suddenly near Bradley, where San Antonio River turns northeastward and joins the Salinas. Although not conspicuous as a topographic feature it can be traced for several miles beyond this point in the low rolling ridge northeast of San Miguel, in San Luis Obispo County. The range has been deeply eroded and many canyons extend far back toward the rounded crest, the average altitude of which is from 2,000 to 2,500 feet. Between the San Antonio Hills and the main Santa Lucia Range is the range known as the Sierra de las Piedras (see Pl. I). It lies between San Antonio and Nacimiento rivers and, like the San Antonio Hills to the northeast, is a divergent ridge from the main range. It extends southeastward to the point where the Nacimiento turns northeastward to join Salinas River, but can be traced geologically to the San Jose Mountains east of the Santa Margarita Valley, in San Luis Obispo County. Its average altitude is 2,000 to 2,500 feet, and it is an inconspicuous feature in the general topography of the region, lying as it does just northeast of the main mountain ridge. In the past there has been much confusion regarding the names of these different ranges. The Salinas Valley is the largest of the intermontane valleys of the Coast Range region. Along the coast it is a broad, fertile valley ranging from 6 to 10 miles wide, gradually narrowing to about 5 miles at Soledad, 30 miles inland. For 25 miles of this distance the valley is walled in by the steep slopes of the Sierra de Salinas and the Gabilan Range, but both drop down near Soledad and the valley widens on the northeast side into a broad mesa, or elevated plain, lying between the Santa Lucia and Mount Diablo ranges. This mesa extends far to the southeast and ends in the arid Carriso Plain, lying east of San Juan River. The mesa has an average width of about 20 miles and rises gently from Salinas River far up the slopes of the Mount Diablo Range. It has been greatly dissected by numerous canyons, which traverse it in a general southwesterly direction. This mesa was traced to the east and northeast of Chalone Peak, where it appears to extend across the ridge between San Benito and Salinas rivers. GEOLOGY. GENERAL GEOLOGY. STRUCTURE. The upper Salinas Valley is a synclinal fold which extends in a northwest-southeast direction between the Mount Diablo and Santa Lucia ranges. The characteristic structure of this fold may be seen by one crossing the valley in a northeasterly direction from the Sierra de las Piedras to the Mount Diablo Range along a line passing through the town of Bradley. The different formations are seen to dip from both sides toward the axis of the fold, in the valley below. In both of the above-mentioned ranges sedimentary rocks fill the troughs of subordinate folds parallel with the main syncline. In general, in and near the mountains, the formations have been compressed into sharp folds, while in the broad Salinas Valley they are practically undisturbed. STRATIGRAPHY. Basement complex.-The Basement complex on which all the unaltered sedimentary rocks of the region rest consists of (1) a series of metamorphic rocks-gneiss, schist, marble, etc.; (2) granitic rocks, chiefly granite, often coarsely porphyritic. The granite has been described by Prof. A. C. Lawson as the Santa Lucia granite." The rocks of the Basement complex form the axes or cores of the Santa Lucia, Gabilan, and Mount Diablo ranges, and evidently extend to a great depth. The age of the metamorphic series is not definitely known, but it is probably as old as the Carboniferous. San Luis formation.-The name San Luis formation has been applied by Dr. H. W. Fairbanks to a group of sedimentary and associated rocks in the San Luis quadrangle. The formation consists of conglomerates, sandstones, shales, jasper, and altered eruptives. These rocks outcrop along the southwestern slope of the Mount Diablo Range in a long, narrow belt, extending the entire length of Monterey County. They here probably rest unconformably on the Basement complex. Dr. Fairbanks has also described rocks belonging to this formation in the Santa Lucia Range, extending along the coast a Bull. Dept. Geology, Univ. California, vol. 1, 1893, p. 9. from Sur River southeastward to San Luis Obispo County." The San Luis formation is considered to be the equivalent of the Franciscan series and is probably of Jurassic age. Vaquero sandstone.-In the Salinas Valley the Vaquero sandstone is a well-defined formation. So far as observed in this region it rests unconformably on the Basement complex and on stratified terranes older than the Neocene, being thus in this locality the oldest known member of the Neocene; in other localities Neocene formations are found below the Vaquero sandstone, indicating that it is not the basal member of the Neocene. The Vaquero formation is a rather coarse, uniformly gray, white or light-yellow quartzose sandstone, with an occasional stratum of granitic pebbles. It is of great thickness along the eastern slope of the Santa Lucia Range, especially in Los Vaqueros Valley; hence the designation proposed by the writer for this series of sandstones. In the Mount Diablo Range it appears at a few points beneath later formations. On the summit of the Mount Diablo Range, around the headwaters of Stone Canyon, there is a series of beds beneath the Monterey shale which may be a portion of the Vaquero or may be older. The Stone Canyon coal beds are in this series. The following fossils have been found in the Vaquero sandstone: Balanus sp.?; Mytilus sp., probably mathewsonii Gabb; Ostrea tayloriana Gabb (Young)?; Ostrea titan Conrad?; Pecten magnolia Conrad; Turritella hoffmanni Gabb?; Chione mathewsonii Gabb; Chione n. sp. (large, characteristic of this horizon); Mactra aff. catilliformis Conrad; Pecten estrellanus Conrad; Pecten (Chlamys) n. sp., S.; Pecten (Plagioctenium) n. sp., A. Monterey shale.-Above the Vaquero sandstone is found the Monterey shale, which, by reason of its peculiar lithologic characteristics, is conspicuous among the rocks of the Coast Range. In Monterey County it is found in a broad belt along the northeastern slope of the Santa Lucia Range and at frequent intervals along the southwestern slope of the Mount Diablo Range. In both ranges it extends southward far beyond Monterey County. It is usually found resting on the Vaquero sandstone, but is also in contact with older formations at several points. This formation consists of an enormous thickness of thin-bedded siliceous shales, with a small amount of limestone and cherts, especially near the base. The shale beds vary in thickness from a fraction of an inch up to 2 feet, and in color from white, through brown and chocolate color, to black. The more porous shales tend to weather white, while the cherts remain brown or black, and the limestone weathers a rusty brown. When first exposed these shales and limestones are dark, often black, with disseminated bituminous and carbonaceous matter. If closely examined under a microscope or with a magnifying glass, they a Jour. Geol., vol. 3, 1895, pp. 416-425, |