Geologic map and digital database of the Porcupine Wash 7.5 minute quadrangle, Riverside County, California

This data set maps and describes the geology of the
Porcupine Wash 7.5 minute quadrangle, Riverside County,
southern California. The quadrangle, situated in Joshua
Tree National Park in the eastern Transverse Ranges
physiographic and structural province, encompasses parts
of the Hexie Mountains, Cottonwood Mountains, northern
Eagle Mountains, and south flank of Pinto Basin. It is
underlain by a basement terrane comprising Proterozoic
metamorphic rocks, Mesozoic plutonic rocks, and Mesozoic
and Mesozoic or Cenozoic hypabyssal dikes. The basement
terrane is capped by a widespread Tertiary erosion
surface preserved in remnants in the Eagle and Cottonwood
Mountains and buried beneath Cenozoic deposits in Pinto
Basin. Locally, Miocene basalt overlies the erosion
surface. A sequence of at least three Quaternary
pediments is planed into the north piedmont of the Eagle
and Hexie Mountains, each in turn overlain by
successively younger residual and alluvial deposits.
The Tertiary erosion surface is deformed and broken by
north-northwest-trending, high-angle, dip-slip faults and
an east-west trending system of high-angle dip- and
left-slip faults. East-west trending faults are younger
than and perhaps in part coeval with faults of the
northwest-trending set.
The Porcupine Wash database was created using ARCVIEW and
ARC/INFO, which are geographical information system (GIS)
software products of Envronmental Systems Research Institute
(ESRI). The database consists of the following items: (1) a
map coverage showing faults and geologic contacts and units,
(2) a separate coverage showing dikes, (3) a coverage
showing structural data, (4) a scanned topographic base at a
scale of 1:24,000, and (5) attribute tables for geologic
units (polygons and regions), contacts (arcs), and
site-specific data (points). The database, accompanied by a
pamphlet file and this metadata file, also includes the
following graphic and text products: (1) A portable document
file (.pdf) containing a navigable graphic of the geologic
map on a 1:24,000 topographic base. The map is accompanied
by a marginal explanation consisting of a Description of Map
and Database Units (DMU), a Correlation of Map and
Database Units (CMU), and a key to point-and line-symbols.
(2) Separate .pdf files of the DMU and CMU, individually.
(3) A PostScript graphic-file containing the geologic map on
a 1:24,000 topographic base accompanied by the marginal
explanation. (4) A pamphlet that describes the database and
how to access it. Within the database, geologic contacts ,
faults, and dikes are represented as lines (arcs), geologic
units as polygons and regions, and site-specific data as
points. Polygon, arc, and point attribute tables (.pat,
.aat, and .pat, respectively) uniquely identify each
geologic datum and link it to other tables (.rel) that
provide more detailed geologic information.

本数据集针对加利福尼亚州南部河滨县的豪猪溪（Porcupine Wash）7.5分钟地形图幅开展地质填图与描述工作。该图幅位于东横断山脉地貌与构造省的约书亚树国家公园境内，涵盖赫克西山脉、科顿伍德山脉、鹰山脉北部以及平托盆地南翼部分区域。其基底地体由元古代变质岩、中生代侵入岩，以及中生代或新生代浅成岩脉构成。基底地体之上覆盖有广泛发育的第三纪侵蚀面，该侵蚀面在鹰山脉与科顿伍德山脉中以残块形式留存，而在平托盆地内则被新生代沉积物掩埋。局部区域内，中新世玄武岩覆于该侵蚀面之上。至少发育三期第四纪山麓剥蚀面，被雕琢于鹰山脉与赫克西山脉的北麓，每一期剥蚀面之上依次覆盖有时代更年轻的残积与冲积沉积物。第三纪侵蚀面受北西北走向的高角度倾滑断层，以及东西走向的高角度倾滑兼左行走滑断层系统的变形与错断。东西走向断层的形成时代晚于北西走向断层组，部分时段可能与其同期。
豪猪溪数据库采用环境系统研究所（Environmental Systems Research Institute，ESRI）旗下的地理信息系统（GIS）软件ARCVIEW与ARC/INFO构建。该数据库包含以下内容：(1) 显示断层、地质接触线与地质单元的地图覆盖层；(2) 单独的岩脉覆盖层；(3) 显示构造数据的覆盖层；(4) 比例尺为1:24000的扫描地形底图；(5) 针对地质单元（多边形与区域）、地质接触线（弧段）以及点位专项数据的属性表。本数据库附带小册子文件与本元数据文件，同时包含以下图文成果：(1) 可导航的1:24000比例尺地形底图版地质地图可移植文档格式（.pdf）文件，该地图附带图廓注记，包括地图与数据库单元说明（DMU）、地图与数据库单元对比表（CMU）以及点、线符号图例；(2) 单独的DMU与CMU的.pdf文件；(3) 附带图廓注记的1:24000比例尺地形底图版地质地图PostScript图形文件；(4) 介绍数据库及访问方法的小册子。在数据库中，地质接触线、断层与岩脉以线（弧段）形式表示，地质单元以多边形与区域形式表示，点位专项数据以点形式表示。多边形、弧段与点位属性表（分别对应.pat、.aat与.pat）可唯一标识每一处地质数据，并将其链接至其他提供更详细地质信息的关联表（.rel）。