Abstract In a brief summary of California geology it is possible to avoid complications by treating most of the Tertiary series as units. Because of the complexity of the Miocene, however, some attention must be given to the subject of its classification into stages. A common classification recognizes the Monterey and the San Pablo groups. The former is divided into Vaqueros, Temblor, and Monterey formations or stages; the latter into Briones, Cierbo, and Neroly (or “Nerola”) formations. These groups are not readily usable, however, except locally in the district east of San Francisco Bay. In most districts where Vaqueros, Temblor, and Monterey formations can be recognized, the Briones and Cierbo are missing or unrecognizable and the Neroly may or may not be represented by the Santa Margarita or some other formation. In order to introduce a little system into the classification, a desirable first step is to abolish the term “Monterey group.” In the broad sense, it is now practically synonymous with Miocene, because, as will be shown later, the type section of the Monterey probably includes beds equivalent to those elsewhere considered to be Santa Margarita; that is, upper San Pablo. As a stage name, Monterey may be used for beds equivalent to those found in the type section of the Monterey shale on the Monterey Peninsula. The base of this section is represented by the post-Temblor Valvulineria californica zone, one of the most widespread microfaunal zones known in the Coast Ranges. It is recognizable in the San Joaquin Valley

This report discusses the geography, systematic geology, structure, and economic deposits in the Coast Ranges of Central California involving nine quadrangles with an area of approximately 2215 square miles of which about a fifth is water. The hills of the Coast Ranges immediately north of San Francisco occupy three north-westward-trending areas which are separated by the San Andreas fault and northern extension of the Haywards fault system. Each area is composed of distinct groups of rock formations. The oldest formations investigated, perhaps of Paleozoic age, consist of metamorphosed sediments, volcanic rocks, and quartz diorite and are exposed in Point Reyes Peninsula. They form a small residual mass of what was probably an extensive coastal land that lay west of the present coast of California but which late in the Tertiary or early in the Pleistocene foundered beneath the Pacific Ocean. This former land area is believed to have furnished many of the sediments laid down during Mesozoic and Tertiary time that are now exposed in the mountains between the San Andreas fault and the Sacramento Valley. The next younger rocks are a thick series of sandstones and associated basic igneous rocks which are widely distributed throughout the Coast Ranges of California and southern Oregon and are known as the Franciscan group. They constitute the surface rock exposures in most of the area between the San Andreas fault and the northern extension of the Haywards fault zone. The Franciscan has a thickness of 7000 feet or more. It contains no fossils except poorly preserved radiolarians in the cherts and Foraminifera in the limestones, which do not permit of an exact age determination. Recently discovered ichthyosaur head bones and teeth from cherts thought to belong to the Franciscan group are closely allied to a species from the lower Portlandian of Europe. From evidence obtained within the mapped area the Franciscan is younger than the time of intrusion of the quartz diorite into the Sur series which may have been during the late Paleozoic. Its upper age limit is uncertain because of fault contacts with the Knoxville formation. It has been considered by other writers from evidence obtained outside of the mapped area as in part contemporaneous with the Knoxville. The area between the Petaluma-Cotati Valley trough and the Sacramento Valley is composed of more than 30,000 feet of Jurassic to Quaternary marine and fresh-water sediments, together with about 1200 feet of Pliocene andesites, rhyolites, and tuffs. These sediments probably accumulated in structural troughs whose areas and physical environments changed greatly during the Cretaceous and Tertiary. The lower portion consists of clay shales and subordinate amounts of sandstone and conglomerate as much as 17,000 feet thick, containing a marine fauna of ammonites, pelecypods, and gastropods. These rocks include the Jurassic and Lower Cretaceous portions of the Knoxville formation and the Upper Cretaceous Chico. Several faunal zones may be distinguished in the Knoxville, but the formation in the mapped area cannot be subdivided on a lithologic basis. The Chico formation consists of interbedded shales and sandstones about 7000 feet thick. The Paleocene is represented by the Martinez formation, and the Eocene in ascending order by the Capay shale and the Domengine and Markley sandstones. The formations of the Paleocene and Eocene series consist of marine sediments ranging in thickness from 2000 to 5000 feet that were deposited in embayments far more restricted in area than the seas of the Upper Jurassic and Cretaceous time. The marine sedimentary formations of the Oligocene and lower part of the Miocene series occupy still more restricted areas than those of the Paleocene and Eocene, and near Carquinez Strait are more than 5000 feet thick. The upper Miocene sand-stones of the San Pablo group are far more widely distributed and are nearly 2500 feet thick. They are characteristically coarse-grained and were deposited in moderately shallow water which locally was brackish or fresh. The Pliocene rocks crop out extensively in the north-central part of the area and consist largely of alternating flows of andesite, basalt, dacite, and rhyolite together with associated tuffs and agglomerates, whose total thickness is 100 to 1200 feet. In Santa Rosa and Petaluma quadrangles marine sandstones contain invertebrate fossils closely allied to those of the Merced formation in San Francisco. The beds in Marin and Sonoma counties are about 250 feet thick and rest unconformably upon the Franciscan group. Near Petaluma Valley they interfinger with tuffs. Before the Pliocene volcanics accumulated the entire area east of the San Andreas fault was folded and faulted, after which it was deeply eroded. The Pliocene volcanics were laid down on the beveled surface of the older rocks and later were moderately folded and broken by normal faults and locally overturned and broken by thrust faults. During the Quaternary period the Coast Ranges in Middle California, in common with areas to the north and south, were undergoing crustal deformation by differential elevation and depression of the numerous fault blocks, some of which at times were temporarily beneath sea level. Stream erosion adjusted to the differentially elevated blocks and left a somewhat obscure record of the complex Quaternary history. Igneous activity was confined mainly to three widely separated epochs. The pre-Knoxville was characterized by intrusions of quartz diorite. The peridotites, gabbros, and basalts associated with the Franciscan group formed during the second epoch of activity in the early part of the late Jurassic. The third was characterized by extrusion of andesitic and rhyolitic materials during the middle and late Pliocene. Volcanoes may have been active during the intervening periods in areas not far from that studied, as tuflaceous products are present in the Oligocene and Miocene sediments. Important associated mineral resources include mercury, magnesite, limestone, road metal, building stone, clays, and surface and ground water.

ABSTRACT The structure and stratigraphy of the Miocene formations east of San Francisco Bay have been described in multiple studies for over a century. We integrated the results of past investigations and provide new data that improve understanding of formation age, the timing of deformation, and the amount of dextral displacement on selected faults. New geologic mapping and better age control show that formations previously inferred to be separate units of different ages are correlative, and new names are proposed for these units. Miocene structures associated with the development of the San Andreas transform system exerted significant control on Miocene deposition in the East Bay area. The developing structure created five distinct stratigraphic sections that are differentiated on the basis of differences in the stratigraphic sequence, lithology, and age. The stratigraphic changes are attributed to significant dextral displacement, syndepositional faulting, and distal interfingering of sediment from tectonically elevated source areas. New stratigraphic evaluations and age control show that prior to ca. 6 Ma, the developing fault system created local tectonically induced uplift as well as spatially restricted subbasins. Regional folding did not occur until after 6 Ma. Past evaluations have inferred significant dextral displacement on some of the faults in the East Bay. The spatial relationships between unique conglomerate clasts and known source areas, as well as the distribution of well-dated and unique tuffs, suggest that dextral displacement on some faults in the East Bay is less than previously reported.

Abstract Exposed near Galeana, Nuevo Leon, are sedimentary deposits and contemporaneous structures that record the rifting and opening of the Gulf of Mexico, passive-margin development, and Laramide compression in the region. A mapping, sedimentologic, and structural study utilizing thin sections, measured sections, aerial photos, and kinematic models has produced a detailed stratigraphic section that records the transition from terrestrial to open-marine deposition and the orientation and timing of deformational events. Triassic to Early Jurassic red beds in the Huizachal Group are composed of fluvial and marine sands. The La Boca and La Joya formations are separated by a polymictic cobble conglomerate. The Callovian Minas Viejas represents the initial stages of marine transgression and the overlying interbedded carbonates and evaporites of the Zuloaga and Olvido Formations were deposited in response to cyclic eustatic sea-level fluctuations. The increase of biodiversity through the upper Jurassic strata reflects a change from restricted to open-marine conditions. Rift-related tectonics and gravity driven brittle extensional features within the carbonates have been overprinted by structures that formed during the Laramide orogeny. The red beds have been folded and faulted into a broad Laramide anticlinorium, in which smaller intrusion cored folds have amplitudes on the order of tens of meters. The decollement for Laramide thin-skinned deformation occurs within an evaporate unit. There is a high degree of structural complexity in the overlying carbonates as indicated by tight folding patterns. By integrating concepts of depositional systems with structural deformation the hypothesis, “There is an exhumed preraft block in the Zuloaga Limestone around San Pablo de Tranquitas.” will be tested.