# Relationship history for MSHA mine 3900827

Current hierarchy: **Northwestern Engineering Company → Hills Materials Company → Lange Sand Pit No 1**

- 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:** Hills Materials Company → Lange Sand Pit No 1; 1950-01-01 to current/open; source msha-controller-operator-history
- **controller_controls_mine:** Northwestern Engineering Company → Lange Sand Pit No 1; 1950-01-01 to current/open; source msha-controller-operator-history
- **controller_controls_operator:** Northwestern Engineering Company → Hills Materials Company; 1950-01-01 to current/open; source msha-controller-operator-history