# Relationship history for MSHA mine 3301587

Current hierarchy: **Martin Marietta Materials Inc → Martin Marietta Materials,Inc. → Ross Gravel**

- 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 → Ross Gravel; 1950-01-01 to current/open; source msha-controller-operator-history
- **operator_operates_mine:** Dravo Basic Materials Company Inc → Ross Gravel; 1950-01-01 to 1995-01-02; source msha-controller-operator-history
- **controller_controls_mine:** Dravo Corp → Ross Gravel; 1950-01-01 to current/open; source msha-controller-operator-history
- **controller_controls_operator:** Dravo Corp → Dravo Basic Materials Company Inc; 1950-01-01 to 1995-01-02; source msha-controller-operator-history
- **operator_operates_mine:** Martin Marietta Aggregates → Ross Gravel; 1995-01-03 to 2005-06-23; source msha-controller-operator-history
- **controller_controls_operator:** Martin Marietta Materials Inc → Martin Marietta Aggregates; 1995-01-03 to 2005-06-23; source msha-controller-operator-history
- **operator_operates_mine:** Martin Marietta Materials,Inc. → Ross Gravel; 2005-06-24 to current/open; source msha-controller-operator-history
- **controller_controls_operator:** Martin Marietta Materials Inc → Martin Marietta Materials,Inc.; 2005-06-24 to current/open; source msha-controller-operator-history