# Relationship history for MSHA mine 1800716

Current hierarchy: **Robison Douglas → Maryland Blue Stone Inc → Blue Mount Quarries**

- 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:** Maryland Blue Stone Inc → Blue Mount Quarries; 1987-04-01 to current/open; source msha-controller-operator-history
- **controller_controls_mine:** Robison Douglas → Blue Mount Quarries; 1987-04-01 to current/open; source msha-controller-operator-history
- **controller_controls_operator:** Robison Douglas → Maryland Blue Stone Inc; 1987-04-01 to current/open; source msha-controller-operator-history