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Floyd Gray

Floyd Gray is a Scientist Emeritus with the USGS Geology, Minerals, Energy, and Geophysics Science Center in Tucson, AZ. Floyd's work with the USGS has included regional geologic studies, metallogenic studies, mineral-resource assessments, and mineral-environmental studies. 

As a mineral resource specialist in the MRP, he studies the genesis and geologic setting of early magmatic and hydrothermal ore deposits and conducts assessments for undiscovered mineral resources in the Southwestern US, northern Mexico, Central America and the Caribbean basin. He is the project chief of the USGS Puerto Rico, U.S. Virgin Islands and Adjacent Areas of the Greater Antilles Quantitative Mineral Resource Assessment project. His recent research efforts have been in the area of flood hazard early warning systems, hydrogeologic framework studies, aqueous and environmental geochemistry, soil geochemistry, and limnology focusing on mineral-related environmental/ecological vulnerabilities resulting from dispersal of metal contaminants from abandoned and newly developing mine lands. Part of the long-term focus has been to understand the physical and biogeochemical processes that control the distribution, transport, and fate of trace elements in aquatic systems.

Education and Certifications

  • M.S. Geology, University of Massachusetts, Amherst, 1982

  • B.A. Earth Science, Anthropology, University of California, Santa Cruz, 1976

Honors and Awards

  • Inaugural Rufus D. Catchings Diversity Award, 2021

Science and Products

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Image shows orange, discolored water in a small canyon

USGS Response to Possible Metals Contamination from Legacy Mines in the Patagonia Mountains Region and Adjacent Areas, Southeast Arizona and a Template for Future Mineral Environmental Emergency Response

USGS is conducting sampling, monitoring, and modeling in the Patagonia Mountains and nearby regions in Arizona to identify contaminant risk potential of legacy and proposed mine sites and to develop classification criteria for predicting vulnerabilities and targeted sources and sinks of metal contaminants.
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Mineral Resources Program, Geology, Minerals, Energy, and Geophysics Science Center
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USGS Response to Possible Metals Contamination from Legacy Mines in the Patagonia Mountains Region and Adjacent Areas, Southeast Arizona and a Template for Future Mineral Environmental Emergency Response

USGS is conducting sampling, monitoring, and modeling in the Patagonia Mountains and nearby regions in Arizona to identify contaminant risk potential of legacy and proposed mine sites and to develop classification criteria for predicting vulnerabilities and targeted sources and sinks of metal contaminants.
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Landsat image of Puerto Rico and Virgin Islands

Mineral Resource Assessment of U.S. Territories of the Caribbean Basin Archipelago including Puerto Rico, U.S. Virgin Islands and Adjacent Areas

Project objectives are to develop a modern probabilistic quantitative mineral resource assessment of Puerto Rico, U.S. Virgin Islands and adjacent geologically similar areas that examines the potential for minerals-based economic development and trade within the region.
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Mineral Resources Program, Geology, Minerals, Energy, and Geophysics Science Center
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Mineral Resource Assessment of U.S. Territories of the Caribbean Basin Archipelago including Puerto Rico, U.S. Virgin Islands and Adjacent Areas

Project objectives are to develop a modern probabilistic quantitative mineral resource assessment of Puerto Rico, U.S. Virgin Islands and adjacent geologically similar areas that examines the potential for minerals-based economic development and trade within the region.
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Geochemistry of Sediment and Associated Leachates from Samples near the Old Yuma Mine, AZ

This data set includes analysis of 38 sediment samples collected near the Old Yuma Mine. The sediment samples were collected from tailings, waste rock, stream sediment, and background locations. All samples were analyzed by a total digestion method, some by the USEPA 3050 method, and some were leached by the USEPA 1312 method.
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Arizona Water Science Center
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Geologic map and hydrogeologic investigations of the upper Santa Cruz River basin, southern Arizona

This report includes an updated geologic map and cross sections of the upper Santa Cruz River basin, southern Arizona. The map and cross sections describe the geometry, thickness, and structure of the Miocene to Holocene units which form the main aquifers in the basin. The report also includes results of new hydrogeologic studies including (1) mapping and defining depth to bedrock based on geophys
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Geology, Minerals, Energy, and Geophysics Science Center, Geosciences and Environmental Change Science Center

Geologic map of the Rio Rico and Nogales 7.5’ quadrangles, Santa Cruz County, Arizona

The Rio Rico and Nogales (Arizona) 1:24,000-scale quadrangles are located in the Basin and Range Province of southern Arizona, and the southern edge of the map is the international border with Sonora, Mexico.  The major urban area is Nogales, a bi-national city known as “the gateway to Mexico.”  Rocks exposed in the map area range in age from Jurassic through Quaternary.  Major physiographic, geol
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Groundwater and Streamflow Information Program, Geosciences and Environmental Change Science Center

Mineral resource potential maps of the North Fork Smith River Roadless Areas, Del Norte County, California, Curry and Josephine counties, Oregon

Geologic map of the Kalmiopsis Wilderness Area, Oregon

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Geology, Energy & Minerals Science Center

Reconnaissance geologic map of the Selma Quadrangle, Josephine County, Oregon

Mineral resource potential map of the Kalmiopsis Wilderness, southwestern Oregon

Under the provisions of the Wilderness Act (Public Law 88-577, September 3, 1964) and the Joint conference Report on Senate Bill 4, 88th Congress, the U.S. Geological Survey and the U.S. Bureau of Mines have been conducting mineral surveys of wilderness and primitive areas. Areas officially designated as "wilderness," wild," or "canoe" when the act was passed were incorporated into the National Wi
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Geology, Energy & Minerals Science Center

Geologic map of the Wild Rogue Wilderness, Coos, Curry, and Douglas counties, Oregon

Maps showing aeromagnetic data and interpretation for the Kalmiopsis Wilderness, southwestern Oregon

The distinctive magnetic properties of the major rock types in the Kalmiopsis Wilderness of southwestern Oregon facilitate interpretation of aeromagenetic data. The region is composed of tectonic slices of magnetic ultramafic, gabboric, and other ophiolitic rocks faulted against  the realitively nonmagnetic Dothan Formation, the equivalent of the Franciscan Complex of Western California. The sharp

Geologic map of the North Fork Smith River Roadless Area, Del Norte County, northern California, and Curry County, Oregon

Mineral resource potential of the Wild Rogue Wilderness (NF105), Coos and Curry Counties, Oregon

No abstract available.

Geochemical map and rock and stream-sediment data from the Wild Rogue Wilderness, Coos and Curry counties, Oregon

The Wild Rogue Wilderness is located in Coos and Curry Counties, southwestern Oregon and covers part of the Bone Mountain, Marial,  and Agness 15' quadrangles (fig. 1). It is an elongate area, 19 mi by 0.8 to 3 mi (31 km by 1.3 to 5 km) and includes approximately 35,818 acres extending from the town of Agness northeast to Mount Bolivar.  The area is characterized by several diverse geologic terran

Maps showing geochemical characteristics of platinum-group elements and gold in rock samples from the Kalmiopsis Wilderness, Southwestern Oregon

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Microbial endophytes and compost improve plant growth in two contrasting types of hard rock mining waste

The re-vegetation of mining wastes with native plants is a comparatively low-cost solution for mine reclamation. However, re-vegetation fails when extreme pH values, low organic matter, or high concentrations of phytotoxic elements inhibit plant establishment and growth. Our aim was to determine whether the combined addition of municipal waste compost and diazotrophic endophytes (i.e., microorgani
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Courtney Creamer, Mary-Catherine Leewis, Francesca C. Governali, John Freeman, Floyd Gray, Emily G. Wright, Andrea L. Foster
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Mineral Resources Program, Geology, Minerals, Energy, and Geophysics Science Center

Mapa metalogenético de América Central y El Caribe

La Asociación de Servicios Geológicos y Mineros de Iberoamérica (ASGMI), bajo los auspicios de la Comisión de la Carta Geológica del Mundo (CCGM) preparó la primera versión del Mapa Metalogénico de América Central y el Caribe. La coordinación general estuvo a cargo del Servicio Geológico Minero Argentino (SEGEMAR), con tres coordinaciones regionales: América Central a cargo del Servicio Geológico
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Eduardo O Zappettini, Gloria Prieto-Rincon, Natalia Amezcua, Santiago Munoz-Tapia, Janeth Sepúlveda-Ospina, Carlos M. Celada-Arango, David Jara, X Cazanas-Diaz, Jorge L. Torres-Zafra, Jorge L. Cobiella-Reguera, Lukas Zürcher, Greta J. Orris, Floyd Gray, Carolina Maldonado-Diaz, Noe Rodriguez, Ramon Mérida-Montiel, Carlos A. Zarruk
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Geology, Minerals, Energy, and Geophysics Science Center

Preliminary geologic map of the Greater Antilles and the Virgin Islands

IntroductionThis geologic map of the Greater Antilles and the Virgin Islands is a compilation of information from the literature, integrated to provide a seamless geologic map of the region. The geology shown on sheet 1 covers Cuba, the island of Hispaniola, which includes Haiti and the Dominican Republic, Jamaica, the Cayman Islands, Puerto Rico, and the U.S. and British Virgin Islands. A second
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Frederic H. Wilson, Greta Orris, Floyd Gray
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Energy and Minerals Mission Area, Ecosystems Mission Area, Alaska Science Center

Probabilistic mineral resource assessment of U.S. Territories of the Caribbean Basin and adjacent areas: Progress report

The U.S. Geological Survey is partnering with the IberoAmerican Association of Geological and Mining Surveys (ASGMI) to conduct an assessment of undiscovered metallic and non-metallic resources in the Greater Antilles region. The assessment plans to provide science-based information on the geologic availability of these resources for development, land-use planning, and decision making. The USGS an
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Lukas Zürcher, Floyd Gray, Stephen Ludington, Frederic H. Wilson, Greta J. Orris, Mark D. Cocker, Mark E. Gettings, Timothy Hayes
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Geology, Minerals, Energy, and Geophysics Science Center

Geologic framework and hydrogeology of the Rio Rico and Nogales 7.5’ quadrangles, upper Santa Cruz Basin, Arizona, with three-dimensional hydrogeologic model

Rapid population growth and declining annual recharge to aquifers in the upper Santa Cruz Basin area of southern Arizona, have increased the demand for additional groundwater resources. This demand is predicted to escalate in the future because of higher temperatures, longer droughts, less aquifer recharge, and decreased river and stream base flow. We conducted geologic studies to help evaluate an
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William R. Page, Mark W. Bultman, D. Paco VanSistine, Christopher M. Menges, Floyd Gray, Michael P. Pantea
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Groundwater and Streamflow Information Program, Geosciences and Environmental Change Science Center

Assessment of geochemical and hydrologic conditions near Old Yuma Mine in Saguaro National Park, Arizona, 2014–17

The Old Yuma Mine is an abandoned copper, lead, zinc, silver, and gold mine located within the boundaries of Saguaro National Park, Tucson Mountain District, Arizona. This study analyzed the geochemistry of sediments associated with the Old Yuma Mine and assessed hydrologic and geochemical conditions of groundwater to evaluate the area surrounding the Old Yuma Mine. The purpose of the study was to
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Kimberly R. Beisner, Floyd Gray
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Water Resources Mission Area, Arizona Water Science Center

Preliminary assessment of porphyry copper deposits in the Sierra Maestra, Cuba

The U.S. Geological Survey’s “three-step” form of mineral-resource assessment was used to obtain a preliminary estimate of copper resources in undiscovered porphyry deposits of the Paleogene Sierra Maestra Arc. Results of this preliminary assessment suggest that a mean of 3.2 undiscovered deposits are likely present. This estimate is comparable to results from an independently-derived porphyry dep
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Lukas Zürcher, Floyd Gray, Timothy Hayes, Greta J. Orris, Mark E. Gettings, Mark D. Cocker, Leila Gass
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Geology, Minerals, Energy, and Geophysics Science Center

Hydrogeologic investigations of the Miocene Nogales Formation in the Nogales Area, Upper Santa Cruz Basin, Arizona

Hydrogeologic investigations were conducted to evaluate the groundwater resource potential for the Miocene Nogales Formation in the Nogales area, southern Arizona. Results indicate that parts of the formation may provide new, deeper sources of groundwater for the area. Geologic mapping determined the hydrogeologic framework of the formation by defining lithologic, mineralogic, and stratigraphic ch
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William R. Page, Floyd Gray, Mark W. Bultman, Christopher M. Menges
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Groundwater and Streamflow Information Program, Geosciences and Environmental Change Science Center

San Pedro River Aquifer Binational Report

The United States and Mexico share waters in a number of hydrological basins and aquifers that cross the international boundary. Both countries recognize that, in a region of scarce water resources and expanding populations, a greater scientific understanding of these aquifer systems would be beneficial. In light of this, the Mexican and U.S. Principal Engineers of the International Boundary and W
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James B. Callegary, Ismael Minjárez Sosa, Elia María Tapia Villaseñor, Placido dos Santos, Rogelio Monreal Saavedra, Franciso Javier Grijalva Noriega, A. K. Huth, Floyd Gray, C. A. Scott, Sharon Megdal, L. A. Oroz Ramos, Miguel Rangel Medina, James M. Leenhouts
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Water Resources Mission Area, Arizona Water Science Center

Hydrologic response of streams restored with check dams in the Chiricahua Mountains, Arizona

In this study, hydrological processes are evaluated to determine impacts of stream restoration in the West Turkey Creek, Chiricahua Mountains, southeast Arizona, during a summer-monsoon season (June–October of 2013). A paired-watershed approach was used to analyze the effectiveness of check dams to mitigate high flows and impact long-term maintenance of hydrologic function. One watershed had been
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Laura M. Norman, Fletcher C. Brinkerhoff, Evan Gwilliam, D. Phillip Guertin, James B. Callegary, David C. Goodrich, Pamela L. Nagler, Floyd Gray
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Western Geographic Science Center

Porphyry copper assessment of Central America and the Caribbean Basin

Mineral resource assessments provide a synthesis of available information about distributions of mineral deposits in the Earth’s crust. The U.S. Geological Survey prepared a probabilistic mineral resource assessment of undiscovered resources in porphyry copper deposits in Central America and the Caribbean Basin in collaboration with geoscientists from academia and the minerals industry. The purpos
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Floyd Gray, Jane M. Hammarstrom, Stephen Ludington, Lukas Zürcher, Carl E. Nelson, Gilpin R. Robinson, Robert J. Miller, Barry C. Moring
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Mineral Resources Program, Geology, Minerals, Energy, and Geophysics Science Center, Geology, Energy & Minerals Science Center

Geochemistry of soils from the San Rafael Valley, Santa Cruz County, Arizona

This study was conducted to determine whether surficial geochemical methods can be used to identify subsurface mineraldeposits covered by alluvium derived from surrounding areas. The geochemical investigation focused on an anomalous geo-physical magnetic high located in the San Rafael Valley in Santa Cruz County, Arizona. The magnetic high, inferred to be asso-ciated with a buried granite intrusio
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Helen W. Folger, Floyd Gray
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Geology, Energy & Minerals Science Center, Geology, Minerals, Energy, and Geophysics Science Center

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