# Relationship history for MSHA mine 3003235

Current hierarchy: **Robert L Burkwit → Phelps Sand & Gravel Inc → PHELPS SAND & GRAVEL INC.**

- Valid-time bounds: inclusive, date granularity
- Null end: open-ended in the upstream history row; not independent proof of present control
- Transaction-time observation: 2026-10-17T05:35:58.500035+00:00

## Valid-time edges

- **operator_operates_mine:** Phelps Sand & Gravel Inc → PHELPS SAND & GRAVEL INC.; 1998-08-01 to current/open; source msha-controller-operator-history
- **controller_controls_mine:** Robert L Burkwit → PHELPS SAND & GRAVEL INC.; 1998-08-01 to current/open; source msha-controller-operator-history
- **controller_controls_operator:** Robert L Burkwit → Phelps Sand & Gravel Inc; 1998-08-01 to current/open; source msha-controller-operator-history