# Relationship history for MSHA mine 1509585

Current hierarchy: **Robinson S S → Blue Gem Energy Company → Prep 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:** Triple W Coal Sales Inc → Prep Plant; 1976-03-01 to 1977-02-02; source msha-controller-operator-history
- **controller_controls_mine:** Watts Calvin L → Prep Plant; 1976-03-01 to 1977-02-02; source msha-controller-operator-history
- **controller_controls_operator:** Watts Calvin L → Triple W Coal Sales Inc; 1976-03-01 to 1977-02-02; source msha-controller-operator-history
- **operator_operates_mine:** Blue Gem Energy Company → Prep Plant; 1977-02-03 to current/open; source msha-controller-operator-history
- **controller_controls_mine:** Robinson S S → Prep Plant; 1977-02-03 to current/open; source msha-controller-operator-history
- **controller_controls_operator:** Robinson S S → Blue Gem Energy Company; 1977-02-03 to current/open; source msha-controller-operator-history