# Relationship history for MSHA mine 3600921

Current hierarchy: **Stanford Energy → Stanford Mining Company → Penn Hill**

- 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:** Penn Hill Coal Corp → Penn Hill; 1950-01-01 to 1975-12-09; source msha-controller-operator-history
- **controller_controls_mine:** Leasure Donald V Jr & Douglas → Penn Hill; 1950-01-01 to 1975-12-09; source msha-controller-operator-history
- **controller_controls_operator:** Leasure Donald V Jr & Douglas → Penn Hill Coal Corp; 1950-01-01 to 1975-12-09; source msha-controller-operator-history
- **controller_controls_mine:** Zapata Corp → Penn Hill; 1974-11-01 to current/open; source msha-controller-operator-history
- **operator_operates_mine:** Mears Coal Company → Penn Hill; 1975-12-10 to 1983-06-30; source msha-controller-operator-history
- **controller_controls_operator:** Zapata Corp → Mears Coal Company; 1975-12-10 to 1983-06-30; source msha-controller-operator-history
- **operator_operates_mine:** Stanford Mining Company → Penn Hill; 1983-07-01 to current/open; source msha-controller-operator-history
- **controller_controls_mine:** Stanford Energy → Penn Hill; 1983-07-01 to current/open; source msha-controller-operator-history
- **controller_controls_operator:** Stanford Energy → Stanford Mining Company; 1983-07-01 to current/open; source msha-controller-operator-history