# Relationship history for MSHA mine 1509522

Current hierarchy: **Sigmon Harold A → Blue Grass Coal Company Inc → No 1 Prep Plant**

- Valid-time bounds: inclusive, date granularity
- Null end: open-ended in the upstream history row; not independent proof of present control
- Transaction-time observation: 2026-10-13T11:19:05.459773+00:00

## Valid-time edges

- **operator_operates_mine:** Blue Grass Coal Company Inc → No 1 Prep Plant; 1976-01-01 to 1976-11-01; source msha-controller-operator-history
- **controller_controls_mine:** Richard M  Johnson → No 1 Prep Plant; 1976-01-01 to 1976-11-01; source msha-controller-operator-history
- **controller_controls_operator:** Richard M  Johnson → Blue Grass Coal Company Inc; 1976-01-01 to 1976-11-01; source msha-controller-operator-history
- **operator_operates_mine:** Blue Grass Coal Company Inc → No 1 Prep Plant; 1976-11-02 to current/open; source msha-controller-operator-history
- **controller_controls_mine:** Sigmon Harold A → No 1 Prep Plant; 1976-11-02 to current/open; source msha-controller-operator-history
- **controller_controls_operator:** Sigmon Harold A → Blue Grass Coal Company Inc; 1976-11-02 to current/open; source msha-controller-operator-history