# Relationship history for MSHA mine 0202557

Current hierarchy: **Robar Enterprises Inc → Hi-Grade Materials → Hi-Grade Materials Bullhead City 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: 2026-10-18T09:31:49.615908+00:00

## Valid-time edges

- **controller_controls_mine:** Robar Enterprises Inc → Hi-Grade Materials Bullhead City Quarry; 1950-01-01 to current/open; source msha-controller-operator-history
- **operator_operates_mine:** Hi-Grade Materials → Hi-Grade Materials Bullhead City Quarry; 1991-04-01 to current/open; source msha-controller-operator-history
- **controller_controls_operator:** Robar Enterprises Inc → Hi-Grade Materials; 1991-04-01 to current/open; source msha-controller-operator-history