# Relationship history for MSHA mine 2301188

Current hierarchy: **Martin Marietta Materials Inc → Gordon Brothers Quarries Inc → Knorr 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: 2026-10-13T11:19:05.459773+00:00

## Valid-time edges

- **operator_operates_mine:** Gordon Brothers Quarries Inc → Knorr Quarry; 1950-01-01 to 1982-02-28; source msha-controller-operator-history
- **controller_controls_mine:** Richardson A E → Knorr Quarry; 1950-01-01 to 1982-02-28; source msha-controller-operator-history
- **controller_controls_operator:** Richardson A E → Gordon Brothers Quarries Inc; 1950-01-01 to 1982-02-28; source msha-controller-operator-history
- **operator_operates_mine:** Gordon Brothers Quarries Inc → Knorr Quarry; 1982-03-01 to current/open; source msha-controller-operator-history
- **controller_controls_mine:** Martin Marietta Materials Inc → Knorr Quarry; 1982-03-01 to current/open; source msha-controller-operator-history
- **controller_controls_operator:** Martin Marietta Materials Inc → Gordon Brothers Quarries Inc; 1982-03-01 to current/open; source msha-controller-operator-history