Markham
Markham is a 128 MW hydroelectric power plant in Mayes County, Oklahoma, operated by Grand River Dam Authority. EIA-860M lists 4 generating units here, inside SPP. Its units entered service in 1964.
As of 2026-07 (inventory dated 2026-07-31) · EIA-860M Preliminary Monthly Electric Generator Inventory · eia.gov/…/july_generator2026.xlsx · eia.gov/…/eia860m
- Nameplate capacity
- 128.4 MW
- 127.4 MW net summer
- Generating units
- 4
- In service
- 1964
- EIA plant ID
- 2980
Where it is
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- County
- Mayes County, Oklahoma
- Coordinates
- 36.2317, -95.1822
- Balancing authority
- SWPP
- Sector
- Electric Utility
Units, technology and status
- Operator of record
- Grand River Dam Authority
- Primary energy source
- Hydro
- Technologies
- Conventional Hydroelectric
- Status
- Operating
Markham: FAQ
- Where is Markham?
- In Mayes County, Oklahoma (OK). The map on this page is placed at the coordinates EIA files for the plant, which locate the site rather than any individual unit.
- How big is Markham?
- 128 MW of nameplate capacity across 4 units, as of the EIA-860M release for 2026-07.
- Who owns Markham?
- EIA-860M names Grand River Dam Authority as the reporting entity. That is the operator of record on the survey, which is not always the ultimate owner.
- Is this the same as Markham LLC?
- Probably, but EIA-860M does not say. The survey records a plant name and a reporting entity — Grand River Dam Authority here — not the project company that holds the asset. Project companies are commonly registered as an LLC carrying the plant's name, so a search for "Markham LLC" usually means this site. This page shows only what EIA files, and does not assert a corporate structure it cannot see.
- Is Markham still running?
- EIA-860M files it as "Operating" for 2026-07. Statuses change monthly, and this page follows the monthly release.