# Relationship history for MSHA mine 2700232

Current hierarchy: **Polycor Inc → Rock Of Ages Corp → Columbia Quarry**

- 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:** Nortek Inc → Columbia Quarry; 1950-01-01 to 1984-02-21; source msha-controller-operator-history
- **operator_operates_mine:** Rock Of Ages Corp → Columbia Quarry; 1979-01-01 to 1984-02-21; source msha-controller-operator-history
- **controller_controls_operator:** Nortek Inc → Rock Of Ages Corp; 1979-01-01 to 1984-02-21; source msha-controller-operator-history
- **controller_controls_mine:** Kurt M  Swenson → Columbia Quarry; 1980-07-23 to 2016-09-20; source msha-controller-operator-history
- **operator_operates_mine:** Rock Of Ages Corp → Columbia Quarry; 1984-02-22 to current/open; source msha-controller-operator-history
- **controller_controls_operator:** Kurt M  Swenson → Rock Of Ages Corp; 1984-02-22 to 2016-09-20; source msha-controller-operator-history
- **controller_controls_mine:** Polycor Inc → Columbia Quarry; 2016-09-21 to current/open; source msha-controller-operator-history
- **controller_controls_operator:** Polycor Inc → Rock Of Ages Corp; 2016-09-21 to current/open; source msha-controller-operator-history