|Abstract:||This data set maps and describes the geology of the Romoland 7.5‘ quadrangle, Riverside 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) 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 Romoland quadrangle is located in the northern part of the Peninsular Ranges Province within the central part of the Perris block, a relatively stable, rectangular in plan view, area located between the Elsinore and San Jacinto fault zones.
The quadrangle is underlain by pre-Cretaceous basement rocks that are intruded by plutonic rocks of the composite, Cretaceous Peninsular Ranges batholith. Within the quadrangle, the batholith is represented by a wide variety of granitic rocks, ranging from granite to gabbro. Segments of two major plutonic complexes are within the quadrangle. In the southern part of the quadrangle is the northern segment of the Paloma Valley ring complex, which is elliptical in plan view and consists of an older ring-dike with two subsidiary short-arced dikes that were emplaced into gabbro by magmatic stoping. Small to large stoped blocks of gabbro are common within the ring-dikes. A younger ring-set of hundreds of thin pegmatite dikes occur largely within the central part of the complex. These pegmatite dikes were emplaced into a domal fracture system, apparently produced by cauldron subsidence, and include in the center of the complex a number of flat-floored granophyre bodies. The granophyre is interpreted to be the result of pressure quenching of pegmatite magma.
Scattered exposures of the upper shallower part of the Domenigoni Valley pluton occur throughout the central and eastern part of the quadrangle. This pluton consists of massive biotite-hornblende granodiorite and tonalite. Common to abundant, equant-shaped, mafic inclusions occur throughout the pluton except in the outermost part which is devoid of all inclusions. The pluton was passively emplaced by piecemeal stoping of a variety of older rocks producing sharp contacts with the country rock (near center of section 23 west of Menifee Road). Rock of the pluton permeates much of the impure quartzite located on the east side of Quail Valley, which represents host rocks immediately above the roof of the pluton. Associated with this pluton is a swarm of latite dikes; the main part of which occurs to the east in the Winchester 7.5‘ quadrangle. Most latite dikes, that occur in both the pluton and adjacent metamorphic rocks, are notably foliated and most have a well developed lineation defined by oriented biotite and (or) hornblende crystals. In the pluton, emplacement of these dikes was controlled by northwest striking joints; in the metamorphic rocks the dikes were emplaced along foliation planes.
Prebatholitic rocks of probable Mesozoic age include a wide variety of sedimentary rocks of greenschist or lower metamorphic grade. Common lithologies include phyllite, lithic graywacke, impure quartzite, metaarkose, and interlayered quartzite and phyllite. Most of the layering and foliation in the metamorphic rocks is structurally transposed layering and is not relic bedding. An exception is relic cross bedding, which is found only locally.
Valley areas in the quadrangle are underlain primarily by