# Relationship history for MSHA mine 0900933

Current hierarchy: **Dravo-Groves → Dravo-Groves Rock Processing Company → Dravo-Groves Rock Processing 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:** Dravo-Groves Rock Processing Company → Dravo-Groves Rock Processing Plant; 1981-02-01 to current/open; source msha-controller-operator-history
- **controller_controls_mine:** Dravo-Groves → Dravo-Groves Rock Processing Plant; 1981-02-01 to current/open; source msha-controller-operator-history
- **controller_controls_operator:** Dravo-Groves → Dravo-Groves Rock Processing Company; 1981-02-01 to current/open; source msha-controller-operator-history