Publications

We present a P wave velocity model derived from active source seismic data collected during the 1994 Los Angeles Region Seismic Experiment. Our model extends previously published upper crustal velocity models to mantle depths. Our model was developed by both ray tracing through a layered model and calculating travel times through a gridded model. It includes an 8-km-thick crustal root...

This spatial digital database for the geology of the San Pedro River Basin in southeastern Arizona was compiled from three maps by Dickinson (1993, 1998, 2000). Mylar originals of the map sheets were scanned, and the resultant images were rectified to a mathematically-generated set of latitude and longitude registration points. Geologic linework was digitized from the rectified images on...

The geologic map and digital database of the San Bernardino Wash quadrangle are products of a regional geologic mapping effort undertaken in the eastern Transverse Ranges in and around Joshua Tree National Park. This investigation, part of the Southern California Areal Mapping Project (SCAMP), is conducted in cooperation with the California Geologic Survey and the National Park Service...

The geologic map of Catalina Core Complex and San Pedro Trough by Dickinson (1992) was digitized for input into a geographic information system (GIS) by the U.S. Geological Survey staff and contractors in 2000-2001. This digital geospatial database is one of many being created by the U.S. Geological Survey as an ongoing effort to provide geologic information in a geographic information...

Volcanic rocks, mostly basalts and some andesites, are interbedded with middle Miocene strata and are overlain by younger rocks throughout the greater part of the Los Angeles Basin, California. Roughly correlative flows, previously dated radiometrically (or paleontologically) at about 16.4 to 10.7 Ma, crop out in five separate regions around the basin perimeter. Los Angeles Basin...

A high-resolution aeromagnetic survey of the Puget Lowland shows details of the Seattle fault zone, an active but largely concealed east-trending zone of reverse faulting at the southern margin of the Seattle basin. Three elongate, east-trending magnetic anomalies are associated with north-dipping Tertiary strata exposed in the hanging wall; the magnetic anomalies indicate where these...

This report tests the usefulness of airborne time-domain electromagnetic (TEM) data on three mineral-resource-related issues: (1) to test whether known mineral deposits at or near the surface display any signal in the TEM data; 2) determine whether TEM data can be used to locate bedrock concealed by basin fill; and (3) if the exposed mineral deposits display a signal in the TEM data, to...

The geologic map and digital database of the Pinto Mountain quadrangle are products of a regional geologic mapping effort undertaken in the eastern Transverse Ranges in and around Joshua Tree National Park. This investigation, part of the Southern California Areal Mapping Project (SCAMP), is conducted in cooperation with the California Geologic Survey and the National Park Service. In...

Terrain modeling, the practice of ground-surface quantification, is an amalgam of Earth science, mathematics, engineering, and computer science. The discipline is known variously as geomorphometry (or simply morphometry), terrain analysis, and quantitative geomorphology. It continues to grow through myriad applications to hydrology, geohazards mapping, tectonics, sea-floor and planetary

The Permian Phosphoria Formation, a petroleum source rock and world-class phosphate deposit, was deposited in an epicratonic successor basin on the western margin of North America. We calculate the seawater circulation in the basin during deposition of the lower ore zone in the Meade Peak Member from the accumulation rates of carbonate fluorapatite and trace elements. The model gives the...

The conceptual framework used by ecologists and biogeochemists must allow for accurate and clearly defined comparisons of carbon fluxes made with disparate techniques across a spectrum of temporal and spatial scales. Consistent with usage over the past four decades, we define "net ecosystem production" (NEP) as the net carbon accumulation by ecosystems. Past use of this term has been...

Filamentous cyanobacterial mats and Fe oxyhydroxide-rich bacterial mats collected near an inactive gold mine in California are enriched in arsenic (As) approximately 1000-fold relative to the waters in contact with them. The predominant organism in the cyanobacterial mat could not be identified using morphological characteristics, but the unique morphology of the sheath-forming β...