# Relationship history for MSHA mine 1901230

Current hierarchy: **Denis J  Dorr → Denis Eng. & Mach Corp. → Riverdale Plant**

- 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

- **controller_controls_mine:** Denis J  Dorr → Riverdale Plant; 1996-11-01 to current/open; source msha-controller-operator-history
- **operator_operates_mine:** Denis Eng. & Mach Corp. → Riverdale Plant; 2012-03-26 to current/open; source msha-controller-operator-history
- **controller_controls_operator:** Denis J  Dorr → Denis Eng. & Mach Corp.; 2012-03-26 to current/open; source msha-controller-operator-history