# Relationship history for MSHA mine 3100037

Current hierarchy: **Polycor Inc → The N. C.  Granite Corp → Mt Airy Mine And Mill**

- Valid-time bounds: inclusive, date granularity
- Null end: open-ended in the upstream history row; not independent proof of present control
- Transaction-time observation: 2026-10-17T05:35:58.500035+00:00

## Valid-time edges

- **operator_operates_mine:** The N. C.  Granite Corp → Mt Airy Mine And Mill; 1950-01-01 to current/open; source msha-controller-operator-history
- **controller_controls_mine:** William  Swift et al → Mt Airy Mine And Mill; 1950-01-01 to 2020-12-31; source msha-controller-operator-history
- **controller_controls_operator:** William  Swift et al → The N. C.  Granite Corp; 1950-01-01 to 2020-12-31; source msha-controller-operator-history
- **controller_controls_mine:** Polycor Inc → Mt Airy Mine And Mill; 2021-01-01 to current/open; source msha-controller-operator-history
- **controller_controls_operator:** Polycor Inc → The N. C.  Granite Corp; 2021-01-01 to current/open; source msha-controller-operator-history