# Relationship history for MSHA mine 3301657

Current hierarchy: **Spring Brothers Gravel Inc → Spring Brothers Gravel Inc → Spring Bros Sand & Gravel Pit & Mil**

- 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:** Spring Brothers Gravel Inc → Spring Bros Sand & Gravel Pit & Mil; 1950-01-01 to current/open; source msha-controller-operator-history
- **controller_controls_mine:** Spring Brothers Gravel Inc → Spring Bros Sand & Gravel Pit & Mil; 1950-01-01 to current/open; source msha-controller-operator-history
- **controller_controls_operator:** Spring Brothers Gravel Inc → Spring Brothers Gravel Inc; 1950-01-01 to current/open; source msha-controller-operator-history