# Relationship history for MSHA mine 1800734

Current hierarchy: **Beverly A  Critchfield → Maryland Minerals Inc → Thayerville 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

- **controller_controls_mine:** Beverly A  Critchfield et al → Thayerville Quarry; 1991-07-01 to current/open; source msha-controller-operator-history
- **operator_operates_mine:** Maryland Minerals Inc → Thayerville Quarry; 1995-03-01 to current/open; source msha-controller-operator-history
- **controller_controls_operator:** Beverly A  Critchfield et al → Maryland Minerals Inc; 1995-03-01 to current/open; source msha-controller-operator-history