# Relationship history for MSHA mine 3600926

Current hierarchy: **Quaker State Corp → Helen Mining Company → Homer City Mine**

- Valid-time bounds: inclusive, date granularity
- Null end: open-ended in the upstream history row; not independent proof of present control
- Transaction-time observation: 2026-10-17T05:35:58.500035+00:00

## Valid-time edges

- **operator_operates_mine:** Helen Mining Company → Homer City Mine; 1950-01-01 to 1984-12-31; source msha-controller-operator-history
- **controller_controls_mine:** NACCO Industries Inc → Homer City Mine; 1950-01-01 to 1984-12-31; source msha-controller-operator-history
- **controller_controls_operator:** NACCO Industries Inc → Helen Mining Company; 1950-01-01 to 1984-12-31; source msha-controller-operator-history
- **operator_operates_mine:** Helen Mining Company → Homer City Mine; 1985-01-01 to current/open; source msha-controller-operator-history
- **controller_controls_mine:** Quaker State Corp → Homer City Mine; 1985-01-01 to current/open; source msha-controller-operator-history
- **controller_controls_operator:** Quaker State Corp → Helen Mining Company; 1985-01-01 to current/open; source msha-controller-operator-history