# Relationship history for MSHA mine 3500495

Current hierarchy: **Knife River Corporation → Knife River Corporation-Northwest → METRO PORTABLE #4**

- 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:** Gresham Sand & Gravel Company → METRO PORTABLE #4; 1950-01-01 to 2000-05-21; source msha-controller-operator-history
- **controller_controls_mine:** Roger  Ekstrom → METRO PORTABLE #4; 1950-01-01 to 2000-05-21; source msha-controller-operator-history
- **controller_controls_operator:** Roger  Ekstrom → Gresham Sand & Gravel Company; 1950-01-01 to 2000-05-21; source msha-controller-operator-history
- **controller_controls_mine:** MDU Resources Group Inc → METRO PORTABLE #4; 1998-03-05 to 2023-05-31; source msha-controller-operator-history
- **operator_operates_mine:** Knife River Corporation-Northwest → METRO PORTABLE #4; 2000-05-22 to current/open; source msha-controller-operator-history
- **controller_controls_operator:** MDU Resources Group Inc → Knife River Corporation-Northwest; 2000-05-22 to 2023-05-31; source msha-controller-operator-history
- **controller_controls_mine:** Knife River Corporation → METRO PORTABLE #4; 2023-06-01 to current/open; source msha-controller-operator-history
- **controller_controls_operator:** Knife River Corporation → Knife River Corporation-Northwest; 2023-06-01 to current/open; source msha-controller-operator-history