Resource Note: High-Temperature Geothermal Resources Above 350°F in the United States
Executive Summary
The United States possesses significant high-temperature geothermal resources exceeding 350°F (177°C), concentrated primarily in the western states along the Pacific Ring of Fire and areas of active volcanism and tectonic activity. According to the 2008 USGS assessment, 241 identified moderate-temperature (90-150°C) and high-temperature (greater than 150°C) geothermal systems are located on private or accessible public lands across 13 states. The total electric power generation potential from identified geothermal systems is estimated at 9,057 MWe, with California containing 59.7% of the total resource, followed by Nevada with 15.4% and Alaska with 7.5%. Current installed geothermal capacity exceeds 2,500 MWe from plants operating in Alaska, California, Hawaii, Idaho, Nevada, and Utah, with the highest-temperature resources primarily located in California's The Geysers, Salton Sea, and Coso fields. Enhanced Geothermal Systems (EGS) technology could potentially unlock an additional 517,800 MWe of capacity from high-temperature, low-permeability rock formations throughout the western United States.
Source: Fourester Research
California High-Temperature Resources
The Geysers Geothermal Field
The Geysers represents the world's largest geothermal field, containing a complex of 18 geothermal power plants drawing steam from more than 350 wells across 30 square miles in Sonoma, Lake, and Mendocino counties. The field produces superheated steam from a greywacke sandstone reservoir with temperatures sufficient for direct steam electricity generation, representing the largest dry steam field in the world. The Geysers generates approximately 1,517 MW of installed capacity and produced about 20% of California's renewable energy in 2019, making it the most significant high-temperature geothermal resource in the United States. The steam reservoir is capped by heterogeneous low-permeability rocks and underlain by a silicic intrusion, with gravitational and seismic studies suggesting a large magma chamber over 4 miles beneath the surface providing the heat source. Since 1997, the field has been recharged through injection of treated wastewater to maintain reservoir pressure and production levels. The resource represents approximately 1,000 MWe of the identified geothermal capacity for California, demonstrating the exceptional nature of this vapor-dominated system.
Salton Sea Geothermal Field
The Salton Sea geothermal system represents a high-enthalpy geothermal resource with temperatures exceeding 300°C (572°F) and highly productive wells producing hypersaline brines exploited by flash and advanced brine handling technologies. Located along the southeastern shore of the Salton Sea in Imperial County, the field consists of eleven active power plants with a combined capacity of approximately 570 MW. The geothermal system is associated with the Salton Sea Buttes volcanic field and sits on the boundary between the North American Plate and the Pacific Plate, creating ideal conditions for high-temperature resource development. The Imperial Valley geothermal area benefits from active tectonic processes that bring the Earth's core heat and magma close to the surface, heating underground water reservoirs to extreme temperatures. Geothermal plants in the region drill one to two miles into the earth to access underground reservoirs containing not only hot water but saline solutions of various dissolved metals, with geothermal fluids pumped through wells under high pressure that flash to steam upon reaching the surface. The resource area includes multiple development zones such as Truckhaven, Westmoreland, Holtville, South Brawley, and East Mesa, representing some of the highest-temperature commercial geothermal resources in the United States.
Coso Geothermal System
The Coso geothermal system lies within the eastern part of a volcanic center containing 38 rhyolite domes and associated basaltic volcanism, with dome field eruptions occurring between 1.0 Ma and 40 ka. Over two decades of drilling and production, integrated geological, geochemical, and geophysical studies have revealed a complex geothermal system with high-temperature resources suitable for electricity generation. The system supports development of 240MW of high-temperature geothermal resources at Coso Hot Springs, representing significant generating capacity from this eastern California resource. The geothermal field is located in Inyo County and benefits from recent volcanic activity that provides the thermal energy necessary for high-temperature resource development. The Coso system demonstrates the potential for substantial power generation from volcanic-associated geothermal resources in the western United States. Multiple decades of successful operation have validated the long-term sustainability and reliability of this high-temperature geothermal resource for commercial electricity generation.
Long Valley Caldera
Long Valley Caldera in Mono County represents another significant high-temperature geothermal resource area associated with recent volcanic activity and caldera formation. The caldera hosts productive hydrothermal systems with evidence of high-temperature resources suitable for power generation, though development has been limited by environmental and regulatory constraints. Technical studies have identified geothermal potential requiring comprehensive geological, geochemical, and geophysical analysis to fully characterize the resource. The area includes the Mammoth Lakes geothermal system, which shows evidence of shallow hydrothermal activity and high-temperature resources associated with the broader Long Valley volcanic system. Surface manifestations include discrete zones of thermal activity and hot springs that indicate subsurface high-temperature resources. The Long Valley system represents significant untapped potential for high-temperature geothermal development in California, though accessing these resources requires careful environmental management and advanced exploration techniques.
Nevada High-Temperature Resources
Brady Hot Springs Geothermal Area
The Brady Hot Springs geothermal field in northwestern Nevada features reservoir temperatures of 180-193°C (356-379°F) at depths of 1-2 km, supporting combined dual flash and binary geothermal power plants with total installed capacity of 26 MWe. The field is dominated by NNE-trending fault blocks bounded by normal faults, with the Brady's fault zone consisting of a complex system of en echelon, primarily WNW-dipping faults that control hydrothermal activity. The geothermal system represents an existing commercial operation that demonstrates the viability of high-temperature resources in Nevada's Basin and Range province. Brady Hot Springs has served as a research site for innovative geothermal technologies and Enhanced Geothermal Systems development, making it an important location for advancing geothermal technology. The resource has operated successfully since 1992, providing long-term validation of the sustainability and commercial viability of Nevada's high-temperature geothermal resources. The field demonstrates the potential for substantial additional high-temperature resource development throughout the Great Basin region of Nevada.
Steamboat Springs Geothermal Field
Steamboat Springs in western Nevada, located south of Reno, represents a significant high-temperature geothermal resource with extensive geothermal activity including hot springs, steam vents, and fumaroles. The Steamboat Geothermal Plant consists of three separate units producing over 24 MW of electricity, with geothermal brine at temperatures of 310-330°F (154-166°C) pumped from nine underground wells extending 590 to 2,700 feet below ground through fractured granite. The wells demonstrate the high-temperature nature of the resource, with drilling through fractured granite requiring specialized equipment and techniques due to the challenging geological conditions. Historical accounts describe Steamboat Springs as among the most geologically interesting in the world, with hot water constantly depositing silica, gold, silver, mercury, antimony, and other minerals held in solution. The area once featured active geysers until geothermal development began in the 1980s, indicating the high-energy nature of the underlying thermal system. The resource has provided reliable electricity generation for decades, demonstrating the long-term viability of Nevada's high-temperature geothermal resources.
Additional Nevada Resources
Nevada hosts 19 geothermal power plants producing more than 486 MW across the Basin and Range province, with multiple sites demonstrating high-temperature resource potential. The McGinnis Hills facility operated by Ormat represents the largest plant with 96 MW capacity, while other significant installations include Steamboat Springs, Brady/Desert Peak, Dixie Valley, Soda Lake, Stillwater, and Beowawe. Dixie Valley represents a flash steam geothermal operation indicative of high-temperature resources, though specific temperature data requires further research. The Beowawe area historically featured some of the tallest natural geysers in North America, with the main geyser erupting 215 feet over the Great Basin Desert before geothermal development, indicating extremely high-temperature subsurface conditions. Nevada's extensive geothermal activity is estimated to include 40-75% of the Great Basin's geothermal systems hidden deep beneath the ground, suggesting vast untapped high-temperature resources throughout the state. The state's position along major tectonic boundaries and areas of high crustal heat flow provides ideal conditions for high-temperature geothermal resource development.
Utah High-Temperature Resources
Roosevelt Hot Springs
The Roosevelt Hot Springs geothermal area near Milford in Beaver County represents Utah's premier high-temperature geothermal resource, with the Blundell geothermal power station operating since 1984. Resource temperatures in production wells usually exceed 271°C (520°F), well above the 350°F threshold, with wells ranging from 640 to 1,830 meters (2,100 to 6,000 feet) in depth. The resource taps geothermal energy from fractured crystalline rock, with wellhead separators used to flash geothermal fluid into liquid and vapor phases. Steam is collected at temperatures between 177 and 204°C (350-400°F) with steam pressure approaching 109 psi, feeding both single-flash and binary power generation units. The plant produces 26 MWe gross (23 MWe net) from the single-flash unit and an additional 11 MWe from the binary power unit, demonstrating the substantial generating capacity available from Utah's high-temperature resources. The long-term operation since 1984 validates the sustainability and commercial viability of Utah's high-temperature geothermal resources.
Additional Utah Resources
The Hatch geothermal area in Beaver County features bottom-hole temperatures near 177°C (350°F) in wells approaching 2,133 meters (7,000 feet) depth, representing another significant high-temperature resource. The area supports a 10-11 MWe binary geothermal power plant consisting of 50 binary power units of 250 kWe each, demonstrating the modular development potential for Utah's geothermal resources. Sulphurdale in Beaver County hosts multiple geothermal power facilities including binary-cycle and steam-turbine generators, indicating additional high-temperature resource potential in the region. Utah's geothermal resources are primarily associated with Basin and Range extensional tectonics and recent volcanic activity that provides the heat source for high-temperature systems. The state's position within the Intermountain Seismic Belt and areas of elevated heat flow creates favorable conditions for additional high-temperature geothermal resource development.
Other Western States
Idaho Resources
Idaho contains 36 identified geothermal systems with electric power generation potential of 333 MWe (mean estimate), indicating significant high-temperature resource potential throughout the state. The state's geothermal resources are associated with the Snake River Plain volcanic province and Basin and Range extension, providing heat sources for high-temperature system development. Idaho's geothermal resources include both low-temperature direct-use applications and higher-temperature resources suitable for electricity generation. Known geothermal resource areas in Idaho demonstrate the potential for additional high-temperature resource exploration and development. The state's geological setting along the Yellowstone hotspot track and areas of recent volcanism creates favorable conditions for high-temperature geothermal resources.
Oregon Resources
Oregon hosts 29 identified geothermal systems with electric power generation potential of 540 MWe (mean estimate), representing substantial high-temperature resource potential. The Newberry Volcano area represents one of Oregon's premier high-temperature geothermal prospects, associated with recent volcanic activity and demonstrated geothermal resource potential. The state's position along the Cascade Range volcanic arc provides heat sources for high-temperature geothermal system development. Oregon's geothermal resources are primarily located in the eastern portion of the state within the Basin and Range province and areas of recent volcanic activity. The state demonstrates significant potential for Enhanced Geothermal Systems development in high-temperature, low-permeability formations.
Alaska and Hawaii
Alaska contains 53 identified geothermal systems with 677 MWe mean generation potential, including high-temperature resources associated with volcanic activity along the Aleutian arc and mainland Alaska. Hawaii's geothermal resources are associated with active volcanism, with the Puna Geothermal Venture operating a 25.7 MWe plant demonstrating high-temperature resource potential. Both states represent frontier areas for high-temperature geothermal development with substantial untapped resource potential.
Enhanced Geothermal Systems Potential
Enhanced Geothermal Systems technology could unlock an estimated 517,800 MWe of electric power generation capacity from high-temperature, low-permeability rock formations across the western United States. The EGS resource is more uniformly distributed across the western states compared to conventional hydrothermal resources, with Nevada (19.86%), Oregon (12.05%), Idaho (13.11%), and Colorado (10.15%) representing the largest potential resources. EGS development focuses on regions characterized by high temperature but low permeability rock formations, requiring engineering to create or enhance permeability necessary for geothermal fluid circulation. The technology represents the potential to access vast high-temperature resources in basement crystalline rocks and other formations where conventional hydrothermal development is not feasible. Current EGS demonstrations at sites like the Frontier Observatory for Research in Geothermal Energy (FORGE) in Utah are advancing the commercial viability of this technology for accessing high-temperature resources.
Market Development and Future Potential
The identified high-temperature geothermal resources above 350°F represent a substantial opportunity for clean baseload electricity generation across the western United States. Current development has accessed only a fraction of the available high-temperature resources, with significant potential for expansion through both conventional hydrothermal development and Enhanced Geothermal Systems technology. Regional variations in development costs, permitting requirements, and transmission infrastructure create different market opportunities across the various high-temperature resource areas. The long-term operation of facilities like The Geysers (since 1960), Roosevelt Hot Springs (since 1984), and Steamboat Springs (since 1986) demonstrates the technical and commercial viability of high-temperature geothermal resources for sustained electricity generation. Future development will likely focus on underexplored regions identified in the USGS assessment, including northeastern Nevada, western Utah, southern Idaho, eastern Oregon, and parts of New Mexico and Colorado where significant geothermal potential exists but few systems have been identified.
Bottom Line
Large-scale utility developers should prioritize exploration and development of California's Salton Sea region, Nevada's Basin and Range province, and Utah's Roosevelt Hot Springs area for accessing the highest-temperature geothermal resources exceeding 350°F with proven commercial viability. Independent power producers seeking reliable baseload renewable energy should focus on established high-temperature fields with existing infrastructure and demonstrated long-term production, particularly The Geysers, Imperial Valley, and established Nevada geothermal areas. Enhanced Geothermal Systems developers should target high heat flow regions identified in the USGS assessment, particularly in Nevada, Idaho, and Oregon where basement temperatures and geological conditions are most favorable for EGS development. Regional energy authorities should establish systematic exploration programs in underexplored areas including northeastern Nevada, western Utah, southern Idaho, and eastern Oregon where geological conditions suggest significant undiscovered high-temperature resources. International geothermal developers should consider partnerships with U.S. companies to access the world's most extensive high-temperature geothermal resources and gain experience with advanced technologies like Enhanced Geothermal Systems that will be applicable to global markets.