# Relationship history for MSHA mine 3500529

Current hierarchy: **Griffin Ralph E → Portland Sand & Gravel Company Inc → Portland Sand & Gravel Company Incorpora**

- 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:** Portland Sand & Gravel Company Inc → Portland Sand & Gravel Company Incorpora; 1950-01-01 to current/open; source msha-controller-operator-history
- **controller_controls_mine:** Griffin Ralph E → Portland Sand & Gravel Company Incorpora; 1950-01-01 to current/open; source msha-controller-operator-history
- **controller_controls_operator:** Griffin Ralph E → Portland Sand & Gravel Company Inc; 1950-01-01 to current/open; source msha-controller-operator-history