# Relationship history for MSHA mine 3500497

Current hierarchy: **Taiheiyo Cement Corp → CalPortland Company → Canby Sand & Gravel DBA CalPortland**

- Valid-time bounds: inclusive, date granularity
- Null end: open-ended in the upstream history row; not independent proof of present control
- Transaction-time observation: 2026-10-18T09:31:49.615908+00:00

## Valid-time edges

- **operator_operates_mine:** Canby Sand & Gravel Co. → Canby Sand & Gravel DBA CalPortland; 1950-01-01 to 2019-04-30; source msha-controller-operator-history
- **controller_controls_mine:** Parker-Northwest Inc → Canby Sand & Gravel DBA CalPortland; 1950-01-01 to 2015-12-22; source msha-controller-operator-history
- **controller_controls_operator:** Parker-Northwest Inc → Canby Sand & Gravel Co.; 1950-01-01 to 2015-12-22; source msha-controller-operator-history
- **controller_controls_mine:** Taiheiyo Cement Corp → Canby Sand & Gravel DBA CalPortland; 1988-01-01 to current/open; source msha-controller-operator-history
- **controller_controls_mine:** Taiheiyo Cement Corp → Canby Sand & Gravel DBA CalPortland; 1990-10-01 to current/open; source msha-controller-operator-history
- **controller_controls_mine:** Nancy L Traverso → Canby Sand & Gravel DBA CalPortland; 2015-12-23 to current/open; source msha-controller-operator-history
- **controller_controls_operator:** Nancy L Traverso → Canby Sand & Gravel Co.; 2015-12-23 to 2019-04-30; source msha-controller-operator-history
- **operator_operates_mine:** CalPortland Company → Canby Sand & Gravel DBA CalPortland; 2019-05-01 to 2022-10-23; source msha-controller-operator-history
- **controller_controls_operator:** Taiheiyo Cement Corp → CalPortland Company; 2019-05-01 to 2022-10-23; source msha-controller-operator-history
- **operator_operates_mine:** CalPortland Company → Canby Sand & Gravel DBA CalPortland; 2022-10-24 to current/open; source msha-controller-operator-history
- **controller_controls_operator:** Taiheiyo Cement Corp → CalPortland Company; 2022-10-24 to current/open; source msha-controller-operator-history