# Relationship history for MSHA mine 4000838

Current hierarchy: **Buzzi S p A → Buzzi Unicem USA → Signal Mountain Cement 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: 2026-10-18T09:31:49.615908+00:00

## Valid-time edges

- **operator_operates_mine:** General Portland Inc → Signal Mountain Cement Co; 1950-01-01 to 1981-11-11; source msha-controller-operator-history
- **controller_controls_mine:** General Portland Inc → Signal Mountain Cement Co; 1950-01-01 to current/open; source msha-controller-operator-history
- **controller_controls_operator:** General Portland Inc → General Portland Inc; 1950-01-01 to 1981-11-11; source msha-controller-operator-history
- **operator_operates_mine:** General Portland Inc → Signal Mountain Cement Co; 1981-11-12 to 1982-08-30; source msha-controller-operator-history
- **controller_controls_mine:** Lafarge S A → Signal Mountain Cement Co; 1981-11-12 to current/open; source msha-controller-operator-history
- **controller_controls_operator:** Lafarge S A → General Portland Inc; 1981-11-12 to 1982-08-30; source msha-controller-operator-history
- **operator_operates_mine:** Buzzi Unicem USA → Signal Mountain Cement Co; 1982-08-31 to current/open; source msha-controller-operator-history
- **controller_controls_mine:** Buzzi S p A → Signal Mountain Cement Co; 1982-08-31 to current/open; source msha-controller-operator-history
- **controller_controls_operator:** Buzzi S p A → Buzzi Unicem USA; 1982-08-31 to current/open; source msha-controller-operator-history