# Relationship history for MSHA mine 3604761

Current hierarchy: **Didier-Werke Ag → North American Refractories Company → Curwensville 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:** North American Refractories Company Inc → Curwensville Mill; 1950-01-01 to 1985-12-31; source msha-controller-operator-history
- **controller_controls_mine:** Allied-Signal Inc → Curwensville Mill; 1950-01-01 to current/open; source msha-controller-operator-history
- **controller_controls_operator:** Allied-Signal Inc → North American Refractories Company Inc; 1950-01-01 to 1985-12-31; source msha-controller-operator-history
- **operator_operates_mine:** North American Refractories Company → Curwensville Mill; 1986-01-01 to current/open; source msha-controller-operator-history
- **controller_controls_mine:** Didier-Werke Ag → Curwensville Mill; 1986-01-01 to current/open; source msha-controller-operator-history
- **controller_controls_operator:** Didier-Werke Ag → North American Refractories Company; 1986-01-01 to current/open; source msha-controller-operator-history