# Relationship history for MSHA mine 3501306

Current hierarchy: **Carla A  Robertson → Robco Inc → Portable Crusher**

- 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:** Robco Inc → Portable Crusher; 1950-01-01 to current/open; source msha-controller-operator-history
- **controller_controls_mine:** Carla A  Robertson et al → Portable Crusher; 1950-01-01 to current/open; source msha-controller-operator-history
- **controller_controls_operator:** Carla A  Robertson et al → Robco Inc; 1950-01-01 to current/open; source msha-controller-operator-history