Conditional use · Planning application
Idaho Power seeks approval for Mayfield substation and 10 miles of transmission lines
The Elmore County Planning and Zoning Commission approved the conditional use permit on April 2, 2026, for a substation on about 66 acres and roughly 10 miles of new lines on about 85 towers, including a crossing over Interstate 84 that connects to an existing Ada County substation.
From the filing
The application's description as it appears in Elmore County's record. See the official record
Idaho Power Company proposes building an electric substation on about 65.6 acres across two parcels in western Elmore County. The project also includes roughly 10 miles of new transmission lines on about 85 towers, including a crossing over Interstate 84 and connections to existing power lines. This January 2026 staff report is a workshop review ahead of public hearings.
Conditional Use Permit with Master Site Plan for Proposed Mayfield Substation and Transmission Lines Project
Project name on file: Idaho Power Mayfield Substation
Timeline
April 2, 2026
Approved
Elmore County Planning and Zoning Commission: Approved (minutes).
April 2, 2026
Public hearing: Elmore County Planning and Zoning Commission
Jan. 22, 2026
Workshop: Elmore County Planning and Zoning Commission
June 17, 2025
Application filed
Documents
Site plans
- Download Completeness determination letter for CUP-2025-25
Elmore County letter finding the Idaho Power substation and transmission line conditional use permit application incomplete, requesting neighbor notification proof and other items.
March 29, 2026 · 404 pages · 82.4 MB · Exhibits
- Download Entitlement site plan sheets for Mayfield substation
Civil site plan sheets for the Idaho Power Mayfield substation exhibits, including entitlement site plan and preliminary grading sheets, filed with the conditional use permit application.
Jan. 19, 2026 · 73 pages · 21.4 MB · Exhibits
Staff reports
- Download Public hearing staff report for Mayfield substation conditional use permit
Elmore County staff report on Idaho Power's proposed Mayfield substation and about 10 miles of transmission lines, for the April 2, 2026 Planning and Zoning hearing.
March 29, 2026 · 27 pages · 108 KB · Staff Report
- Download Public workshop staff report
Staff report for the January 22, 2026 public workshop on Idaho Power's proposed Mayfield Substation and transmission lines conditional use permit with master site plan.
Jan. 19, 2026 · 16 pages · 69 KB · Staff Report