How big is Mammoth Pool?

Mammoth Pool has a reported capacity of 190 MW. Source: EIA Form 860.

What kind of plant is Mammoth Pool?

Mammoth Pool is a Conventional Hydroelectric facility in Madera County, CA, participating in the CAISO market.

Where is Mammoth Pool located?

Mammoth Pool is in Madera County, CA, inside the CAISO balancing area.

Who operates Mammoth Pool?

Mammoth Pool is operated by Southern California Edison Co according to the EIA generator inventory. Reporting membership does not by itself establish ultimate ownership.

When did Mammoth Pool start operating?

Mammoth Pool reports a commercial operation date of 1960. Current status: operating. Source: EIA Form 860.

How much electricity does Mammoth Pool generate?

Mammoth Pool reported 593.9 GWh over the twelve months to 2026-04. Figures are net generation as filed to EIA-923.

Where does Mammoth Pool connect to the grid?

Mammoth Pool interconnects at Substation adjacent to Mammoth Pool Powerhouse, on the Southern California Edison Company system.

How does Mammoth Pool compare to other plants?

By capacity, Mammoth Pool ranks #73 of 1,349 operating plants of the same technology nationally. It ranks #9 of 210 in CA.

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Conventional HydroelectricCAISO · Madera County

Mammoth Pool

Southern California Edison Company · Madera County · CAISO

Mammoth Pool is a hydroelectric facility with 190 MW of EIA-reported operating capacity in Madera County, California, registered as EIA Plant ID 344. Southern California Edison Co owns and operates the plant. The plant's generating configuration is conventional hydroelectric facility with two Francis-type vertical-shaft hydraulic-reaction turbine units, each rated at 100,000 HP and 360 rpm. Commercial operation began in 1960. The facility interconnects at Substation adjacent to Mammoth Pool Powerhouse at 230 kV.

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plant:plant-344

Ask about Mammoth Pool

Investigate technology, capacity, output, price behavior, ownership, and related facilities using this profile plus current grid data.

Overview

Key fields

Reported capacity: 190 MW
EIA-reported operating capacity; nameplate, seasonal, AC/DC, and unit ratings may differ.
Technology: Conventional Hydroelectric
Primary generation technology.
Registry anchor: Plant 344
Southern California Edison Co · Madera County · CAISO
Operating status: Operating
Mammoth Pool is operating.
Grid connection: Substation adjacent to Mammoth Pool Powerhouse
230 kV · Southern California Edison Company
Commercial operation: 1960
Best-supported operating milestone.

Profile

Grid role: Reservoir-storage hydroelectric generation coordinated with the Big Creek Hydroelectric System and optimized for generation during runoff and peak-demand periods.
Grid connection: Substation adjacent to Mammoth Pool Powerhouse · 230 kV · Southern California Edison Company.
Physical build: Mammoth Pool is a hydroelectric project consisting of Mammoth Pool Dam and Reservoir, a 39,350-foot power tunnel, surge chamber, rock trap, a single 1,988-foot penstock, Mammoth Pool Powerhouse, transmission facilities, and a separate fishwater-generator installation. The powerhouse contains two Francis-type vertical-shaft hydraulic reaction turbines and two main generators; the fishwater installation contains one Pelton-type turbine and generator. The project was constructed by Bechtel Corporation for Southern California Edison, with construction completed in early 1960.

Structured profile

Reported capacity: 190 MW
Conventional Hydroelectric
Commercial operation: 1960
Operating status: operating
Mammoth Pool is operating.
Interconnection: Substation adjacent to Mammoth Pool Powerhouse
230 kV · Southern California Edison Company
Location

Units and generators

Operating generator records and technology attributes reported through EIA-860.

Generator	Capacity	Technology	Operation	Status
1	95 MW 95 MW summer	Conventional Hydroelectric Water · HY	Mar 1960	Operating
2	95 MW 95 MW summer	Conventional Hydroelectric Water · HY	Mar 1960	Operating

Performance

Monthly EIA generation history and recent market-resource behavior where linked telemetry is available.

Peer context

Technology capacity: 190 MW
National rank: #73
CA rank: #9

Monthly generation

Download CSV

Latest 12 months

593.9 GWh

Reported net generation

Latest report

Apr 2026

EIA-923 monthly filing

2025 capacity factor

28.0%

Grid and market context

Deterministic links to ERCOT market resources, price records, outage disclosures, queue records, and nearby infrastructure. Candidate joins remain labeled until corroborated.

Nearby substations

HIFLD infrastructure inventory

MAMMOTH

IN SERVICE · 230 kV

0.0 km

BIG CREEK 8

Commercial, land, and environmental record

Source-backed project transactions, agreements, land records, permits, and environmental disclosures. Portfolio and adjacent-project facts remain explicitly scoped.

Transactions and agreements

Operating Agreement

Jun 1, 1957

The Mammoth Pool Operating Contract was entered into by SCE and the U.S. Bureau of Reclamation governing Mammoth Pool operations, including SCE's right to divert and store water for hydroelectric power and domestic use, subject to specified storage and water-use constraints.

Southern California Edison Company · U.S. Bureau of Reclamation

Southern California Edison Company,, 18 FPC 829 (1957)

Land and environmental record

Environmental Permit

May 31, 2019

Final Clean Water Act Section 401 Water Quality Certification

The California State Water Resources Control Board issued the final Section 401 Water Quality Certification on May 31, 2019 for the six Big Creek Hydroelectric Projects, including Mammoth Pool (FERC No. 2085).

Mammoth Pool Hydroelectric Project | California State Water Resources Control Board

Project Land Area And Landowner

Jun 3, 2019

Approximately 2,030 acres of U.S. Forest Service land

The Mammoth Pool Hydroelectric Project is located in Fresno and Madera Counties on the upper San Joaquin River and occupies approximately 2,030 acres of national forest land administered by the United States Forest Service.

Mammoth Pool Hydroelectric Project | California State Water Resources Control Board

Water Source And Discharge

Jun 3, 2019

Upper San Joaquin River, Rock Creek, and Ross Creek

Water is diverted at Mammoth Pool Reservoir and from Rock and Ross Creeks. Water passing through the powerhouse enters the San Joaquin River upstream of the Dam 6 impoundment (Big Creek No. 3 forebay).

Mammoth Pool Hydroelectric Project | California State Water Resources Control Board

Related parties and identifiers

Parties, market resources, and identifiers tied to this asset, with owner, operator, developer, EPC, compliance provider, and interconnecting entity roles kept separate.

Relationship graph

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AssetOwner / operatorRelated asset

Parties and identifiers

Timeline and sources

Project milestones and public references behind the asset profile.

Project timeline

Jun 4, 1951
Jun 4, 1951
Original license application filedSource
Southern California Edison Company filed the application for a license for the proposed Mammoth Pool Project, FERC Project No. 2085.
Dec 30, 1957
Dec 30, 1957

Reporting portfolio

EIA reporting entity

Southern California Edison Co

Entity 17609

Operating portfolio

34 plants

1 states

Reported capacity

2,702.4 MW

Batteries · Conventional Hydroelectric · Hydroelectric Pumped Storage

Largest reported plants in this portfolio
Largest reported plants	Capacity	State
Mountainview Generating Station	1,036.8 MW	CA
Cathode (Hinson) BESS	200 MW	CA
J S Eastwood	199.8 MW	CA
Mammoth PoolCurrent	190 MW	CA
Big Creek 3	174.5 MW	CA
Separator (Etiwanda) BESS	112.5 MW	CA
Big Creek 4	100 MW	CA
Big Creek 1	88.4 MW	CA

Portfolio membership follows the latest EIA-860 reporting entity. It does not imply ultimate ownership.

View full reporting portfolio

Ask about Mammoth Pool

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Overview

Key fields

Profile

Structured profile

Units and generators

Performance

Peer context

Monthly generation

Grid and market context

Nearby substations

Commercial, land, and environmental record

Transactions and agreements

Land and environmental record

Related parties and identifiers

Relationship graph

Parties and identifiers

Timeline and sources

Project timeline

Reporting portfolio

Sources

Common questions about Mammoth Pool

How big is Mammoth Pool?

What kind of plant is Mammoth Pool?

Where is Mammoth Pool located?

Who operates Mammoth Pool?

When did Mammoth Pool start operating?

How much electricity does Mammoth Pool generate?

Where does Mammoth Pool connect to the grid?

How does Mammoth Pool compare to other plants?

Co-located assets

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