The Geysers KGRA Analysis

The Geysers-Calistoga Known Geothermal Resource Area (KGRA) encompasses a vast territory spanning across Sonoma, Lake, Mendocino, and Napa counties in Northern California, with the broader geothermal resource field covering 117 square kilometers (45 square miles). Calpine Corporation currently operates as the primary developer, controlling 28,447 acres (44 square miles) of the active geothermal development zone through 13 operating geothermal power plants, making it the largest generator of electricity from geothermal resources in the United States. The field utilizes 319 steam production wells and 73 injection wells, representing a total of 601 wells drilled to date by Calpine, demonstrating substantial infrastructure investment in the steam-dominated western portion of the KGRA. Development has been concentrated primarily in the steam-dominated western and central areas near the Sonoma-Lake County border, where the dry steam reservoir provides optimal conditions for electricity generation. The current 18 operating plants generate approximately 900MW of the field's estimated 1,517MW total installed capacity, indicating that roughly 60% of the identified geothermal reservoir capacity has been developed for electricity generation. Historical studies from the 1970s and 1980s identified Lake County as containing "most of the undeveloped resource" with significant untapped potential remaining in the eastern portions of the KGRA, particularly in areas with hot water resources that have not yet been commercially developed due to technological and economic constraints.

Appendix: Cities and Communities within The Geysers KGRA

Developed Areas (Active Geothermal Operations)

Primary Development Zone:

Anderson Springs (Sonoma County) - Location of NCPA Geothermal Plant No. 2 (55MW facility)
Geyserville (Sonoma County) - Historic gateway community to The Geysers, served as early tourist destination
The Geysers Complex - Central steam field with 13 active Calpine power plants

Communities within KGRA Boundaries

Lake County Communities:

Middletown - Largest community in the area, regional service center
Cobb - Small mountain community near geothermal development
Loch Lomond - Small residential community
Anderson Springs - Community adjacent to geothermal facilities
Hidden Valley - Rural residential area
Seigler Springs - Small community in eastern KGRA

Sonoma County Communities:

Geyserville - Historic town, original gateway to The Geysers resort
Cloverdale - Northern boundary community
Healdsburg - Regional hub south of KGRA

Mendocino County:

Hopland - Northwestern boundary area

Napa County:

Calistoga - Eastern boundary, terminus of historical railroad access
Pope Valley - Eastern KGRA area

Development Status by Area

Heavily Developed Areas:

Western Steam Field (Sonoma/Lake County border) - Primary concentration of 13 operating power plants
Central Geysers - Core steam production area with majority of 319 production wells
Anderson Springs vicinity - NCPA and other independent facilities

Underdeveloped/Undeveloped Areas:

Eastern KGRA (Lake County) - Contains significant hot water resources not yet commercially developed
Northern sections (Mendocino County portions) - Limited exploration and development
Southeastern areas (Napa County portions) - Peripheral to main steam field, minimal development
Clear Lake vicinity - Eastern Lake County areas with identified but undeveloped geothermal potential

Infrastructure Notes

Emergency notification sirens installed in Middletown, Anderson Springs, Cobb, and Loch Lomond (2018)
South Lake County Fire Protection District serves multiple communities and geothermal facilities
Transportation access via Highway 175, Highway 29, and local geothermal service roads
Calpine operates visitor center in Middletown for public education and tours

Research Note: The Geysers-Calistoga Known Geothermal Resource Area (KGRA)