# Relationship history for MSHA mine 4300134

Current hierarchy: **Polycor Inc → Rock Of Ages Corp → Derby 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

- **operator_operates_mine:** Derby Granite Inc → Derby Quarry; 1950-01-01 to 1980-07-22; source msha-controller-operator-history
- **controller_controls_mine:** Bianchi Irio → Derby Quarry; 1950-01-01 to 1980-07-22; source msha-controller-operator-history
- **controller_controls_operator:** Bianchi Irio → Derby Granite Inc; 1950-01-01 to 1980-07-22; source msha-controller-operator-history
- **operator_operates_mine:** Rock Of Ages Corp → Derby Quarry; 1980-07-23 to current/open; source msha-controller-operator-history
- **controller_controls_mine:** Kurt M  Swenson → Derby Quarry; 1980-07-23 to 2016-09-20; source msha-controller-operator-history
- **controller_controls_operator:** Kurt M  Swenson → Rock Of Ages Corp; 1980-07-23 to 2016-09-20; source msha-controller-operator-history
- **controller_controls_mine:** Polycor Inc → Derby 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