# Relationship history for MSHA mine 4502757

Current hierarchy: **Buchan John F & Chris Nicholls → Horizon Sand & Gravel → Horizon Sand & Gravel**

- 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:** Chapman Sand & Gravel → Horizon Sand & Gravel; 1980-02-01 to 1985-09-10; source msha-controller-operator-history
- **controller_controls_mine:** Chapman Sanford → Horizon Sand & Gravel; 1980-02-01 to 1985-09-10; source msha-controller-operator-history
- **controller_controls_operator:** Chapman Sanford → Chapman Sand & Gravel; 1980-02-01 to 1985-09-10; source msha-controller-operator-history
- **operator_operates_mine:** Greenline Gravel → Horizon Sand & Gravel; 1985-09-11 to 1989-04-30; source msha-controller-operator-history
- **controller_controls_mine:** Jane A  Hallock → Horizon Sand & Gravel; 1985-09-11 to 1989-04-30; source msha-controller-operator-history
- **controller_controls_operator:** Jane A  Hallock → Greenline Gravel; 1985-09-11 to 1989-04-30; source msha-controller-operator-history
- **operator_operates_mine:** Horizon Sand & Gravel → Horizon Sand & Gravel; 1989-05-01 to current/open; source msha-controller-operator-history
- **controller_controls_mine:** Buchan John F & Chris Nicholls → Horizon Sand & Gravel; 1989-05-01 to current/open; source msha-controller-operator-history
- **controller_controls_operator:** Buchan John F & Chris Nicholls → Horizon Sand & Gravel; 1989-05-01 to current/open; source msha-controller-operator-history