# Relationship history for MSHA mine 1301121

Current hierarchy: **Holcim Ltd → Northwestern States Portland Cement Company → Willowbrook Shale Pit**

- 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:** Northwestern States Portland Cement Company → Willowbrook Shale Pit; 1950-01-01 to 1990-01-18; source msha-controller-operator-history
- **controller_controls_mine:** Jack  MacNider → Willowbrook Shale Pit; 1950-01-01 to current/open; source msha-controller-operator-history
- **controller_controls_operator:** Jack  MacNider → Northwestern States Portland Cement Company; 1950-01-01 to 1990-01-18; source msha-controller-operator-history
- **operator_operates_mine:** Northwestern States Portland Cement Company → Willowbrook Shale Pit; 1990-01-19 to current/open; source msha-controller-operator-history
- **controller_controls_mine:** Holcim Ltd → Willowbrook Shale Pit; 1990-01-19 to current/open; source msha-controller-operator-history
- **controller_controls_operator:** Holcim Ltd → Northwestern States Portland Cement Company; 1990-01-19 to current/open; source msha-controller-operator-history