# Relationship history for MSHA mine 1002212

Current hierarchy: **Darrell B  Derr → William Derr & Sons, Inc. → Portable Screen**

- 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:** William Derr & Sons, Inc. → Portable Screen; 2010-09-08 to current/open; source msha-controller-operator-history
- **controller_controls_mine:** Darrell B  Derr → Portable Screen; 2010-09-08 to current/open; source msha-controller-operator-history
- **controller_controls_operator:** Darrell B  Derr → William Derr & Sons, Inc.; 2010-09-08 to current/open; source msha-controller-operator-history