# Relationship history for MSHA mine 0402297

Current hierarchy: **Cph Sub Inc & Marine Magnesium Management Company → Marine Magnesium Company → Columbia 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:** Merck & Company Inc → Columbia Quarry; 1950-01-01 to 1989-02-28; source msha-controller-operator-history
- **controller_controls_mine:** Merck & Company Inc → Columbia Quarry; 1950-01-01 to 1989-02-28; source msha-controller-operator-history
- **controller_controls_operator:** Merck & Company Inc → Merck & Company Inc; 1950-01-01 to 1989-02-28; source msha-controller-operator-history
- **operator_operates_mine:** Marine Magnesium Company → Columbia Quarry; 1989-03-01 to current/open; source msha-controller-operator-history
- **controller_controls_mine:** Cph Sub Inc & Marine Magnesium Management Company → Columbia Quarry; 1989-03-01 to current/open; source msha-controller-operator-history
- **controller_controls_operator:** Cph Sub Inc & Marine Magnesium Management Company → Marine Magnesium Company; 1989-03-01 to current/open; source msha-controller-operator-history