# Relationship history for MSHA mine 1900362

Current hierarchy: **Chisholm W D → W D Chisholm Company → Boxborough Pit And 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: 2026-10-17T05:35:58.500035+00:00

## Valid-time edges

- **operator_operates_mine:** Stow Sand & Gravel Inc → Boxborough Pit And Mill; 1950-01-01 to 1979-06-30; source msha-controller-operator-history
- **controller_controls_mine:** Bry Irene K → Boxborough Pit And Mill; 1950-01-01 to 1979-06-30; source msha-controller-operator-history
- **controller_controls_operator:** Bry Irene K → Stow Sand & Gravel Inc; 1950-01-01 to 1979-06-30; source msha-controller-operator-history
- **operator_operates_mine:** W D Chisholm Company → Boxborough Pit And Mill; 1979-07-01 to current/open; source msha-controller-operator-history
- **controller_controls_mine:** Chisholm W D → Boxborough Pit And Mill; 1979-07-01 to current/open; source msha-controller-operator-history
- **controller_controls_operator:** Chisholm W D → W D Chisholm Company; 1979-07-01 to current/open; source msha-controller-operator-history