# Relationship history for MSHA mine 3401982

Current hierarchy: **Philip J  Schwarz Et At; Gene J  Schwarz → Hefner Sand, L.L.C. → Douglas 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

- **operator_operates_mine:** Hefner Sand, L.L.C. → Douglas Plant; 2005-12-20 to current/open; source msha-controller-operator-history
- **controller_controls_mine:** Gene J  Schwarz Et Al → Douglas Plant; 2005-12-20 to current/open; source msha-controller-operator-history
- **controller_controls_operator:** Gene J  Schwarz Et Al → Hefner Sand, L.L.C.; 2005-12-20 to current/open; source msha-controller-operator-history
- **controller_controls_operator:** Philip J  Schwarz Et At → Hefner Sand, L.L.C.; 2005-12-20 to current/open; source msha-controller-operator-history