# Relationship history for MSHA mine 1508228

Current hierarchy: **Blair David → T B S Mining Inc → No 4 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:** T B S Mining Inc → No 4 Surface; 1950-01-01 to 1975-04-09; source msha-controller-operator-history
- **controller_controls_mine:** Blair David → No 4 Surface; 1950-01-01 to current/open; source msha-controller-operator-history
- **controller_controls_operator:** Blair David → T B S Mining Inc; 1950-01-01 to 1975-04-09; source msha-controller-operator-history
- **operator_operates_mine:** Clarke & Lawson Construction Co → No 4 Surface; 1975-04-10 to 1977-05-03; source msha-controller-operator-history
- **controller_controls_mine:** Clarke & Lawson Construction Co → No 4 Surface; 1975-04-10 to 1977-05-03; source msha-controller-operator-history
- **controller_controls_operator:** Clarke & Lawson Construction Co → Clarke & Lawson Construction Co; 1975-04-10 to 1977-05-03; source msha-controller-operator-history
- **operator_operates_mine:** T B S Mining Inc → No 4 Surface; 1977-05-04 to current/open; source msha-controller-operator-history
- **controller_controls_operator:** Blair David → T B S Mining Inc; 1977-05-04 to current/open; source msha-controller-operator-history