Mammoth Pacific II — United States of America

Mammoth Pacific II is a 15 MW geothermal power plant in California, United States of America. It is operated by Ormat Nevada Inc. Based on reported annual generation of 69 GWh, it can supply roughly 20k homes. It ranks #5132 of 10,884 United States of America power plants by installed capacity. Commissioned in 1991, it is around 35 years old — long-established. As a non-combustion source, it has no direct CO₂ emissions from generation. In context, geothermal supplies about 0.4% of United States of America's electricity; the national grid averages 384 gCO₂/kWh (43.0% low-carbon) (2025).

Plant data: WRI Global Power Plant Database (CC BY 4.0), id USA0010481.

Data provenance

Capacity and fuel are the upstream open-dataset record, not yet matched to a 2026 registry or GEM entry.

capacity: WRI GPPD; fuel: WRI GPPD

In context: how this plant compares

At 15 MW, Mammoth Pacific II is below the median geothermal plant in United States of America (30 MW). Geothermal plants tap underground heat to raise steam for a turbine; they provide steady, low-carbon baseload but are limited to geologically active regions.

Capacity comparison computed from the WRI Global Power Plant Database; fuel-type context is general engineering background.

Key facts

Load factor

52%, from 69 GWh of reported generation, in line with the 52% median for 60 geothermal plants in United States of America

Generation trend

80 GWh in 2013 and 69 GWh in 2019 (−14%)

Highest and lowest year

2013: 80 GWh; 2015: 58 GWh

Share of United States of America geothermal capacity

0.4% of 3,889 MW across 65 plants in this dataset

Age among peers

23 of 65 dated geothermal plants in United States of America are older

Calculated from the capacity and generation records in this dataset (WRI Global Power Plant Database (CC BY 4.0)).

Reported generation trend

Annual generation (GWh), WRI Global Power Plant Database (CC BY 4.0).

Owner

Operated by Ormat Nevada Inc. All plants by this company →

Local climate & thermal context

This geothermal plant taps underground heat to raise steam that drives a turbine. It sits in a warm-summer Mediterranean climate (Köppen Csb) — Northern Hemisphere, latitude 37.6°N — which shapes how much energy it can produce and how its output varies through the year.

Monthly mean temperature

Heating degree-days here run 83% above the median power plant in this dataset — a proxy for how much extra energy heated equipment must replace through its surfaces in winter.

Climate heat-demand index: 90/100 — this site sits in the top third of the power plants we cover by heating degree-days.

Climate normals: WorldClim 2.1 (1970–2000 monthly normals, 10 arc-min, CC BY 4.0); zone: Köppen-Geiger world climate classification (Kottek et al. 2006, 0.5° grid). Degree-days & heat-demand index computed by PowerAtlas — a modelled heat-demand proxy, not a measured site figure.

Site climate & environmental severity

This site sits in a mild atmospheric environment (estimated ISO 9223 class C2 — Low), with humidity / wetness the leading environmental stress.

Indicative estimate via the ISO 9223:2012 informative method (atmospheric corrosivity from temperature, time-of-wetness and airborne salinity), using WorldClim climate normals, the Köppen-Geiger class and coast distance. Indicative, not a measured corrosion rate.

How it compares & nearby plants

The #55 largest geothermal power plant of 65 in United States of America by capacity.

United States of America has 65 geothermal power plants in this dataset, together about 3,889 MW of capacity.

Nearby power plants

• Ples I · Geothermal · 15 MW · California
• Mammoth Pacific I · Geothermal · 10 MW · California
• Rush Creek · Hydro · 13.1 MW · California
• Upper Gorge · Hydro · 37.5 MW · California
• Middle Gorge · Hydro · 37.5 MW · California
• Control Gorge · Hydro · 37.5 MW · California

Location

Coordinates 37.6464, -118.9092 from WRI Global Power Plant Database (CC BY 4.0). View on OpenStreetMap.

Frequently asked questions