# Relationship history for MSHA mine 2500900

Current hierarchy: **Olson Donald → Valley Sand & Gravel Company → Big Springs Pit**

- 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

- **controller_controls_mine:** Olson Donald → Big Springs Pit; 1950-01-01 to current/open; source msha-controller-operator-history
- **operator_operates_mine:** Valley Sand & Gravel Company → Big Springs Pit; 1978-03-09 to current/open; source msha-controller-operator-history
- **controller_controls_operator:** Olson Donald → Valley Sand & Gravel Company; 1978-03-09 to current/open; source msha-controller-operator-history