# Relationship history for MSHA mine 1200638

Current hierarchy: **David L  Schrock → Schrock Excavating Inc → CHRISTNER SCHROCK AGGREGATE CO.**

- 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:** Christner Gravel Company Inc → CHRISTNER SCHROCK AGGREGATE CO.; 1950-01-01 to 1992-12-31; source msha-controller-operator-history
- **controller_controls_mine:** Paul  Christner → CHRISTNER SCHROCK AGGREGATE CO.; 1950-01-01 to 1992-12-31; source msha-controller-operator-history
- **controller_controls_operator:** Paul  Christner → Christner Gravel Company Inc; 1950-01-01 to 1992-12-31; source msha-controller-operator-history
- **operator_operates_mine:** Christner Gravel Company Inc → CHRISTNER SCHROCK AGGREGATE CO.; 1993-01-01 to 1996-10-21; source msha-controller-operator-history
- **controller_controls_mine:** Phyllis  Begley → CHRISTNER SCHROCK AGGREGATE CO.; 1993-01-01 to 1996-10-21; source msha-controller-operator-history
- **controller_controls_operator:** Phyllis  Begley → Christner Gravel Company Inc; 1993-01-01 to 1996-10-21; source msha-controller-operator-history
- **operator_operates_mine:** Schrock Excavating Inc → CHRISTNER SCHROCK AGGREGATE CO.; 1996-10-22 to current/open; source msha-controller-operator-history
- **controller_controls_mine:** David L  Schrock → CHRISTNER SCHROCK AGGREGATE CO.; 1996-10-22 to current/open; source msha-controller-operator-history
- **controller_controls_operator:** David L  Schrock → Schrock Excavating Inc; 1996-10-22 to current/open; source msha-controller-operator-history