MAPPING AND PETROGRAPHIC ANALYSIS OF LOST CANYON AND DELKER CANYON WITHIN THE EASTERN SAN GABRIEL MOUNTAINS

Lost Canyon and Delker Canyon are located within the Eastern San Gabriel Mountains in Southern California and drain the north part of Ontario Ridge into Icehouse Canyon. The purpose of our research is to map and correlate units between these tributary canyons and further examine structural and metamorphic relationships within the San Gabriel Mountains. Previous work in this specific area (Ehlig, 1958) was somewhat cursory and lumped many of the units together. These canyons are primarily composed of Proterozoic metasedimentary units intruded by at least two distinct generations of Mesozoic plutons. A Brunton compass and GPS receiver were used to measure and locate geologic features and create a geologic map. Metasedimentary units within the area generally strike northwest and dip northeast. From most abundant to least, these include (1) biotite schist or gneiss with quartz, altered plagioclase and at times porphyroblastic garnets, (2) calc-silicate gneiss containing calcite, diopside and grossular garnet, (3) orthoquartzite or feldspathic quartzite, and (4) white marble. Several dip reversals suggest that the section is repeated by folds. Detailed structural analysis is ongoing. Calsilicate exposed in lower Lost Canyon is the source of spectacularly folded boulders that may be viewed at mile 1.8 of the Icehouse Canyon trail. Younger intrusions include a large body of biotite hornblende granodiorite in the east and several large dikes of leucocratic biotite granite. The granite is younger than the granodiorite, based on unique structural trends and crosscutting field relations. Major faults within these two canyons trend northwest and display primarily thrust movement along with some components of strike-slip that were determined by measuring slicken lines on fault plane surfaces. Preliminary analysis indicates that at least two distinct tectonic events have occurred within this area resulting in ductile deformation and recrystallization followed by brittle faulting. Our data provides a more in-depth understanding of previous depositional environments, geological units present within this area, and how tectonic evolution of the San Gabriel Mountains influenced features of Icehouse Canyon and its tributary canyons.