Geologic map of the Fifteenmile Valley 7.5' quadrangle, San Bernardino County, California

This data set maps and describes the geology of the Fifteenmile Valley 7.5' quadrangle,
San Bernardino County, 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) 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), an index map, a regional geologic and structure
map, and a key for point and line symbols; (2) PDF files of this Readme (including the
metadata file as an appendix), Description of Map Units (DMU), and a screen graphic of the
plot produced by the PostScript plot file.
The geologic map covers the northernmost part of the San Bernardino Mountains and the
southern Granite Mountains. These two bedrock areas are separated by the wide, alluviated
Fifteenmile Valley. Bedrock units in the San Bernardino Mountains are dominated by large
Cretaceous granitic bodies ranging in composition from monzogranite to gabbro, and include
lesser Triassic monzonite. The Granite Mountains are underlain chiefly by large Triassic
monzonite bodies, and in the western part, by Cretaceous and possibly Jurassic
monzogranite to monzodiorite. Spanning the Pleistocene in age, large alluvial fans, flank
the north side of the San Bernardino Mountains, and are dominated by debris flow deposits.
The central part of Fifteenmile Valley is covered by fine grained alluvial material
deposited by streams flowing into Rabbit Lake and an unnamed dry lake in the northwestern
part of the quadrangle. Young, south dipping reverse faults, some with moderately to well
eroded fault scarps, discontinuously flank the northern edge of the San Bernardino
Mountains. Young and old high-angle faults are mapped within both the San Bernardino and
Granite Mountains.
The geologic map database contains original U.S. Geological Survey data generated by
detailed field observation and by interpretation of aerial photographs. The map was
compiled on a base-stable cronoflex copy of the Fifteenmile Valley 7.5' topographic base
and then scribed. This scribe guide was used to make a 0.007 mil blackline clear-film,
which was scanned at 1200 DPI by Optronics Specialty Company, Northridge, California;
minor hand-digitized additions were made at the USGS. Lines, points, and polygons were
subsequently edited at the USGS 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 as 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圣贝纳迪诺县十五英里谷（Fifteenmile Valley）7.5′分幅图幅的地质状况开展制图与描述工作。本数据集依托环境系统研究所（Environmental Systems Research Institute）的ARC/INFO地理信息软件构建，其数据库包含以下内容：(1) 包含地质接触界线与地质单元的地图覆盖层；(2) 针对地质单元（多边形要素）、接触界线（弧段要素）以及专项点位数据（点要素）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、地形数据、人文地理数据、地质单元对比图（Correlation of Map Units, CMU）、地质单元说明图（Description of Map Units, DMU）、索引图、区域地质构造图以及点线符号图例的PostScript绘图文件；(2) 包含本说明文档（附录含元数据文件）、地质单元说明图（DMU）以及PostScript绘图文件生成的屏幕预览图的PDF文件。

本次制图覆盖圣贝纳迪诺山脉最北端与花岗岩山脉南部区域，两处基岩区域被宽阔的冲积型十五英里谷分隔开来。圣贝纳迪诺山脉的基岩单元以大型白垩纪花岗岩体为主，其岩性从二长花岗岩至辉长岩不等，同时包含少量三叠纪二长岩。花岗岩山脉的基底主要为大型三叠纪二长岩体，其西部区域则以白垩纪（或许还有侏罗纪）的二长花岗岩至二长闪长岩为主。圣贝纳迪诺山脉北麓发育形成于更新世的大型冲积扇，其主要沉积物为泥石流堆积物。十五英里谷中部区域被细粒冲积物覆盖，这些沉积物由汇入兔湖（Rabbit Lake）以及本图幅西北部一处无名干湖的溪流携带沉积而成。圣贝纳迪诺山脉北缘断续分布着向南倾的年轻逆冲断层，部分断层带有侵蚀程度中等至严重的断层崖。圣贝纳迪诺山脉与花岗岩山脉范围内均发育有不同时期的高角度断层。

本地质图数据库包含美国地质调查局（U.S. Geological Survey, USGS）通过详细野外踏勘与航片解译生成的原始数据。本图以十五英里谷7.5′分幅地形底图的克朗福莱克斯（cronoflex）复印底版为基准进行编绘，随后进行刻图作业。以此刻图底版为基准制作了0.007密耳的黑线透明胶片，该胶片由加利福尼亚州北岭市的奥普特罗尼克斯特种公司（Optronics Specialty Company）以1200 DPI的分辨率进行扫描；美国地质调查局随后对部分内容进行了手动数字化增补。美国地质调查局随后使用标准ARC/INFO指令对线条、点与多边形要素进行了编辑处理。所有在1:24000比例尺下可被辨识的数字化与编辑瑕疵均已得到修正。在本数据库中，地质接触界线以线条（弧段）表示，地质单元以多边形表示，专项点位数据以点要素表示。多边形、弧段与点要素属性表（分别对应.pat、.aat与.pat文件）可唯一标识每一处地质数据项。