# Relationship history for MSHA mine 1401492

Current hierarchy: **Martin Marietta Materials Inc → Martin Marietta Aggregates → PORTABLE PLANT #2**

- 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:** Martin Marietta Materials Inc → PORTABLE PLANT #2; 1950-01-01 to current/open; source msha-controller-operator-history
- **controller_controls_mine:** David S  Walker → PORTABLE PLANT #2; 1950-01-01 to current/open; source msha-controller-operator-history
- **operator_operates_mine:** Walker Stone Company Inc → PORTABLE PLANT #2; 1985-10-01 to 2001-08-02; source msha-controller-operator-history
- **controller_controls_operator:** David S  Walker → Walker Stone Company Inc; 1985-10-01 to 2001-08-02; source msha-controller-operator-history
- **operator_operates_mine:** Martin Marietta Aggregates → PORTABLE PLANT #2; 2001-08-03 to current/open; source msha-controller-operator-history
- **controller_controls_operator:** Martin Marietta Materials Inc → Martin Marietta Aggregates; 2001-08-03 to current/open; source msha-controller-operator-history