# Relationship history for MSHA mine 1506857

Current hierarchy: **Potter Hobert E → Joan Coal Company → Surface**

- 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:** Joan Coal Company → Surface; 1973-01-01 to current/open; source msha-controller-operator-history
- **controller_controls_mine:** Potter Hobert E → Surface; 1973-01-01 to current/open; source msha-controller-operator-history
- **controller_controls_operator:** Potter Hobert E → Joan Coal Company; 1973-01-01 to current/open; source msha-controller-operator-history