# Relationship history for MSHA mine 0503935

Current hierarchy: **Martin Marietta Materials Inc → Martin Marietta Materials → Walstrum Quarry**

- 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

- **controller_controls_mine:** Martin Marietta Materials Inc → Walstrum Quarry; 1950-01-01 to current/open; source msha-controller-operator-history
- **controller_controls_mine:** Albert R  Frei → Walstrum Quarry; 1950-01-01 to current/open; source msha-controller-operator-history
- **operator_operates_mine:** Albert Frei & Sons Inc → Walstrum Quarry; 1984-03-01 to 2024-01-12; source msha-controller-operator-history
- **controller_controls_operator:** Albert R  Frei → Albert Frei & Sons Inc; 1984-03-01 to 2024-01-12; source msha-controller-operator-history
- **operator_operates_mine:** Martin Marietta Materials → Walstrum Quarry; 2024-01-13 to current/open; source msha-controller-operator-history
- **controller_controls_operator:** Martin Marietta Materials Inc → Martin Marietta Materials; 2024-01-13 to current/open; source msha-controller-operator-history