# Relationship history for MSHA mine 1400830

Current hierarchy: **H T  Ritchie → Quality Rock Company → Douglas 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:** Martin Marietta Aggregates → Douglas Quarry; 1950-01-01 to 1981-05-07; source msha-controller-operator-history
- **controller_controls_mine:** Martin Marietta Materials Inc → Douglas Quarry; 1950-01-01 to current/open; source msha-controller-operator-history
- **controller_controls_operator:** Martin Marietta Materials Inc → Martin Marietta Aggregates; 1950-01-01 to 1981-05-07; source msha-controller-operator-history
- **controller_controls_mine:** H T  Ritchie → Douglas Quarry; 1981-05-01 to current/open; source msha-controller-operator-history
- **operator_operates_mine:** Quality Rock Company → Douglas Quarry; 1981-05-08 to current/open; source msha-controller-operator-history
- **controller_controls_operator:** H T  Ritchie → Quality Rock Company; 1981-05-08 to current/open; source msha-controller-operator-history