# Relationship history for MSHA mine 4201920

Current hierarchy: **Chevron Corporation → American Gilsonite Company → B-16**

- 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

- **controller_controls_mine:** Chevron Corporation → B-16; 1950-01-01 to current/open; source msha-controller-operator-history
- **controller_controls_mine:** Demar  Boren → B-16; 1980-07-01 to current/open; source msha-controller-operator-history
- **operator_operates_mine:** Demar Boren Mining Inc → B-16; 1985-02-01 to 1986-07-31; source msha-controller-operator-history
- **controller_controls_operator:** Demar  Boren → Demar Boren Mining Inc; 1985-02-01 to 1986-07-31; source msha-controller-operator-history
- **operator_operates_mine:** American Gilsonite Company → B-16; 1986-08-01 to current/open; source msha-controller-operator-history
- **controller_controls_operator:** Chevron Corporation → American Gilsonite Company; 1986-08-01 to current/open; source msha-controller-operator-history