# Relationship history for MSHA mine 3500432

Current hierarchy: **Simpson Richard → Yankton Paving & Rock → St Helens 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:** Dwight Irby Construction Company → St Helens Quarry; 1950-01-01 to 1978-12-31; source msha-controller-operator-history
- **controller_controls_mine:** Irby Dwight Construction Company → St Helens Quarry; 1950-01-01 to 1978-12-31; source msha-controller-operator-history
- **controller_controls_operator:** Irby Dwight Construction Company → Dwight Irby Construction Company; 1950-01-01 to 1978-12-31; source msha-controller-operator-history
- **operator_operates_mine:** Yankton Paving & Rock → St Helens Quarry; 1979-01-01 to current/open; source msha-controller-operator-history
- **controller_controls_mine:** Simpson Richard → St Helens Quarry; 1979-01-01 to current/open; source msha-controller-operator-history
- **controller_controls_operator:** Simpson Richard → Yankton Paving & Rock; 1979-01-01 to current/open; source msha-controller-operator-history