# Relationship history for MSHA mine 0600018

Current hierarchy: **Rio Tinto Group → U S Silica Company → Ledyard Plant**

- 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:** Connecticut Silica Company → Ledyard Plant; 1950-01-01 to 1986-12-31; source msha-controller-operator-history
- **controller_controls_mine:** Ottawa Silica Company → Ledyard Plant; 1950-01-01 to 1986-12-31; source msha-controller-operator-history
- **controller_controls_operator:** Ottawa Silica Company → Connecticut Silica Company; 1950-01-01 to 1986-12-31; source msha-controller-operator-history
- **controller_controls_mine:** Rio Tinto Group → Ledyard Plant; 1986-04-02 to current/open; source msha-controller-operator-history
- **operator_operates_mine:** U S Silica Company → Ledyard Plant; 1987-01-01 to current/open; source msha-controller-operator-history
- **controller_controls_operator:** Rio Tinto Group → U S Silica Company; 1987-01-01 to current/open; source msha-controller-operator-history