# Relationship history for MSHA mine 2300993

Current hierarchy: **Mertens Construction Company Inc → Mertens Construction Co., Inc. → Mertens Clay Pits**

- 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

- **operator_operates_mine:** A P Green Refractories Inc → Mertens Clay Pits; 1950-01-01 to 1979-06-30; source msha-controller-operator-history
- **controller_controls_mine:** USG Corporation → Mertens Clay Pits; 1950-01-01 to current/open; source msha-controller-operator-history
- **controller_controls_operator:** USG Corporation → A P Green Refractories Inc; 1950-01-01 to 1979-06-30; source msha-controller-operator-history
- **controller_controls_mine:** Mertens Construction Company Inc → Mertens Clay Pits; 1950-01-01 to current/open; source msha-controller-operator-history
- **operator_operates_mine:** Mertens Construction Co., Inc. → Mertens Clay Pits; 1979-07-01 to current/open; source msha-controller-operator-history
- **controller_controls_operator:** Mertens Construction Company Inc → Mertens Construction Co., Inc.; 1979-07-01 to current/open; source msha-controller-operator-history