# Relationship history for MSHA mine 3301750

Current hierarchy: **National Lime & Stone Co. → National Lime & Stone Company → Upper Sandusky 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:** National Lime & Stone Co. → Upper Sandusky Plant; 1950-01-01 to current/open; source msha-controller-operator-history
- **operator_operates_mine:** H & M Sand & Gravel Company → Upper Sandusky Plant; 1950-01-01 to 1988-08-31; source msha-controller-operator-history
- **controller_controls_mine:** Ivan D  Hobbs → Upper Sandusky Plant; 1950-01-01 to 1988-08-31; source msha-controller-operator-history
- **controller_controls_operator:** Ivan D  Hobbs → H & M Sand & Gravel Company; 1950-01-01 to 1988-08-31; source msha-controller-operator-history
- **operator_operates_mine:** National Lime & Stone Company → Upper Sandusky Plant; 1988-09-01 to current/open; source msha-controller-operator-history
- **controller_controls_operator:** National Lime & Stone Co. → National Lime & Stone Company; 1988-09-01 to current/open; source msha-controller-operator-history