# Relationship history for MSHA mine 1506725

Current hierarchy: **Envirodyne Industries → Benham Coal Inc → No 2 B Wisconsin Steel Mine**

- 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

- **operator_operates_mine:** International Harvester Company → No 2 B Wisconsin Steel Mine; 1950-01-01 to 1977-08-11; source msha-controller-operator-history
- **controller_controls_mine:** International Harvester Company → No 2 B Wisconsin Steel Mine; 1950-01-01 to 1977-08-11; source msha-controller-operator-history
- **controller_controls_operator:** International Harvester Company → International Harvester Company; 1950-01-01 to 1977-08-11; source msha-controller-operator-history
- **operator_operates_mine:** Benham Coal Inc → No 2 B Wisconsin Steel Mine; 1977-08-12 to current/open; source msha-controller-operator-history
- **controller_controls_mine:** Envirodyne Industries → No 2 B Wisconsin Steel Mine; 1977-08-12 to current/open; source msha-controller-operator-history
- **controller_controls_operator:** Envirodyne Industries → Benham Coal Inc; 1977-08-12 to current/open; source msha-controller-operator-history