# Relationship history for MSHA mine 4200164

Current hierarchy: **Chevron Corporation → Chevron Chemical Company → Vernal Mill**

- 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:** Stauffer Chemical Company → Vernal Mill; 1950-01-01 to 1981-02-22; source msha-controller-operator-history
- **controller_controls_mine:** Unilever United States Inc → Vernal Mill; 1950-01-01 to current/open; source msha-controller-operator-history
- **controller_controls_operator:** Unilever United States Inc → Stauffer Chemical Company; 1950-01-01 to 1981-02-22; source msha-controller-operator-history
- **operator_operates_mine:** Chevron Chemical Company → Vernal Mill; 1981-02-23 to current/open; source msha-controller-operator-history
- **controller_controls_mine:** Chevron Corporation → Vernal Mill; 1981-02-23 to current/open; source msha-controller-operator-history
- **controller_controls_operator:** Chevron Corporation → Chevron Chemical Company; 1981-02-23 to current/open; source msha-controller-operator-history