# Relationship history for MSHA mine 0504211

Current hierarchy: **Montrose County-Co → Montrose County → PORTABLE SCREENER**

- 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

- **controller_controls_mine:** Montrose County-Co → PORTABLE SCREENER; 1950-01-01 to current/open; source msha-controller-operator-history
- **operator_operates_mine:** Montrose County → PORTABLE SCREENER; 1987-03-01 to current/open; source msha-controller-operator-history
- **controller_controls_operator:** Montrose County-Co → Montrose County; 1987-03-01 to current/open; source msha-controller-operator-history