Geologic Map of the Corona North 7.5' Quadrangle, Riverside and San Bernardino Counties, California

This data set maps and describes the geology of the Corona North 7.5' quadrangle, Riverside and San Bernardino Counties, California. Created using Environmental Systems Research Institute's ARC/INFO software, the data base consists of the following items: (1) a map coverage containing geologic contacts and units, (2) a coverage containing structural data, (3) a coverage containing geologic unit annotation and leaders, and (4) attribute tables for geologic units (polygons), contacts (arcs), and site-specific data (points). In addition, the data set includes the following graphic and text products: (1) a postscript graphic plot-file containing the geologic map, topography, cultural data, a Correlation of Map Units (CMU) diagram, a Description of Map Units (DMU), and a key for point and line symbols, and (2) PDF files of the Readme (including the metadata file as an appendix), and the graphic produced by the Postscript plot file.
The Corona North quadrangle is located near the northern end of the Peninsular Ranges Province. All but the southeastern tip of the quadrangle is within the Perris block, a relatively stable, rectangular in plan area located between the Elsinore and San Jacinto fault zones. The southeastern tip of the quadrangle is barely within the Elsinore fault zone.
The quadrangle is underlain by Cretaceous plutonic rocks that are part of the composite Peninsular Ranges batholith. These rocks are exposed in a triangular-shaped area bounded on the north by the Santa Ana River and on the south by Temescal Wash, a major tributary of the Santa Ana River. A variety of mostly silicic granitic rocks occur in the quadrangle, and are mainly of monzogranite and granodioritic composition, but range in composition from micropegmatitic granite to gabbro. Most rock units are massive and contain varying amounts of meso- and melanocratic equant-shaped inclusions. The most widespread granitic rock is monzogranite of the Cajalco pluton, a large pluton that extends some distance south of the quadrangle. North of Corona is a body of micropegmatite that appears to be unique in the batholith rocks.
Diagonally bisecting the quadrangle is the Santa Ana River. North of the Santa Ana River alluvial deposits are dominated by the distal parts of alluvial fans emanating from the San Gabriel Mountains north of the quadrangle. Widespread areas of the fan deposits are covered by a thin layer of wind blown sand.
Alluvial deposits in the triangular-shaped area between the Santa Ana River and Temescal Wash are quite varied, but consist principally of locally derived older alluvial fan deposits. These deposits rest on remnants of older, early Quaternary or late Tertiary age, nonmarine sedimentary deposits that were derived from both local sources and sources as far away as the San Bernardino Mountains. These deposits in part were deposited by an ancestral Santa Ana River. Older are a few scattered remnants of late Tertiary (Pliocene) marine sandstone that include some conglomerate lenses. Clasts in the conglomerate include siliceous volcanic rocks exotic to this part of southern California. This sandstone was deposited as the southeastern-most part of the Los Angeles sedimentary marine basin and was deposited along a rocky shoreline developed in the granitic rocks, much like the present day shoreline at Monterey, California. Most of the sandstone and granitic paleoshoreline features have been removed by quarrying and grading in the area of Porphyry north to Highway 91. Excellent exposures in highway road cuts still remain on the north side of Highway 91 just east of the 91-15 interchange and on the east side of U.S. 15 just north of the interchange.
South of Temescal Wash is a series of both younger and older alluvial fan deposits emanating from the Santa Ana Mountains to the southeast. In the immediate southwest corner of the quadrangle is a small exposure of sandstone and pebble conglomerate of the Sycamore Canyon member of the Puente Formation of early Pliocene and Miocene age and sandstone and conglomerate of undivided Sespe and Vaqueros Formations of early Miocene, Oligocene, and late Eocene age.
The geologic map data base contains original U.S. Geological Survey data generated by detailed field observation recorded on 1:24,000 scale aerial photographs. The map was created by transferring lines from the aerial photographs to a 1:24,000 scale topographic base. The map was digitized and lines, points, and polygons were subsequently edited using standard ARC/INFO commands. Digitizing and editing artifacts significant enough to display at a scale of 1:24,000 were corrected. Within the database, geologic contacts are represented as lines (arcs), geologic units are polygons, and site-specific data as points. Polygon, arc, and point attribute tables (.pat, .aat, and .pat, respectively) uniquely identify each geologic datum.

本数据集针对加利福尼亚州里弗赛德县与圣贝纳迪诺县的科罗纳北7.5′四边形地质图幅的地质情况进行了制图与描述。本数据库采用环境系统研究所（Environmental Systems Research Institute, ESRI）的ARC/INFO软件构建，包含以下内容：(1) 包含地质接触界线与地质单元的地图覆盖层；(2) 包含构造数据的覆盖层；(3) 包含地质单元注记与指引线的覆盖层；(4) 针对地质单元（多边形）、接触界线（弧段）以及点位专项数据的属性表。此外，本数据集还包含以下图文成果：(1) 包含地质图、地形、人文数据、地质单元对比图（Correlation of Map Units, CMU）、地质单元描述图（Description of Map Units, DMU）以及点位与线符号图例的Postscript图形绘图文件；(2) 自述文件（含作为附录的元数据文件）的PDF文件，以及由该Postscript绘图文件生成的图形PDF文件。

科罗纳北图幅位于半岛山脉省（Peninsular Ranges Province）北端附近。该图幅除东南部尖端外，全部落入佩里斯地块（Perris block）——一个位于埃尔西诺尔断裂带与圣哈辛托断裂带之间、相对稳定的平面呈矩形的地块。图幅的东南部尖端仅少量处于埃尔西诺尔断裂带范围内。

该图幅基底为白垩纪深成岩，属于复合半岛岩基（Peninsular Ranges batholith）的一部分。这些岩石出露于一个以圣安娜河为北界、以圣安娜河主要支流特梅斯卡尔干谷（Temescal Wash）为南界的三角形区域内。图幅内出露多种以长英质为主的花岗岩类岩石，主要为二长花岗岩与花岗闪长岩类，成分范围从微文象花岗岩到辉长岩不等。多数岩石单元呈块状，含有不同数量的中色与暗色等轴状包裹体。分布最广泛的花岗岩类岩石为卡哈尔科深成岩体（Cajalco pluton）的二长花岗岩，该大型深成岩体向南延伸至图幅以外一段距离。科罗纳以北发育一处微文象岩体，在该岩基岩石中似乎较为独特。

圣安娜河斜向贯穿该图幅。圣安娜河北侧的冲积沉积以来自图幅北侧圣盖博山脉的冲积扇远端沉积为主。广泛分布的扇积物被一层薄的风成砂覆盖。

圣安娜河与特梅斯卡尔干谷之间的三角形区域内的冲积沉积种类繁多，但主要为本地物源的老旧冲积扇沉积。这些沉积覆于早更新世或晚第三纪的老旧非海相沉积残余之上，这些沉积物既来自本地物源，也来自远至圣贝纳迪诺山脉的物源。部分沉积物由古圣安娜河沉积形成。

晚第三纪（上新世）的海相砂岩零星残存，其中包含若干砾岩透镜体。砾岩中的砾石包括南加州该区域罕见的硅质火山岩。该砂岩作为洛杉矶海相沉积盆地的最东南部分沉积而成，沉积于发育在花岗岩类岩石中的岩质岸线，与现今加利福尼亚州蒙特雷的岸线颇为相似。在从斑岩（Porphyry）地区向北至91号公路的区域内，大部分砂岩与古岩岸地貌已因采石与平整作业被移除。但在91号与15号高速公路交汇处东侧以北的91号公路北侧，以及15号美国国道交汇处北侧东侧，仍保留有高速公路路堑中的优质露头。

特梅斯卡尔干谷南侧发育一系列来自东南侧圣安娜山脉的新老冲积扇沉积。图幅西南角紧邻区域出露少量上新世早期与中新世的普恩特组（Puente Formation）西卡莫峡谷段砂岩与砾岩，以及早中新世、渐新世与始新世晚期的未划分的塞斯佩组与瓦克罗组砂岩与砾岩。

本地质图数据库源自美国地质调查局（U.S. Geological Survey, USGS）的原始野外实测数据，这些数据基于1:24000比例尺航空照片记录的详细野外观测成果。该图通过将航空照片上的界线转绘至1:24000比例尺地形底图而制作完成。图件经数字化后，使用标准ARC/INFO命令对线条、点位与多边形进行了编辑。所有足以在1:24000比例尺下显现的数字化与编辑瑕疵均已修正。在数据库中，地质接触界线以线（弧段）表示，地质单元以多边形表示，点位专项数据以点表示。多边形、弧段与点位属性表（分别对应.pat、.aat与.pat格式）可唯一标识每一处地质数据项。