# Relationship history for MSHA mine 2103120

Current hierarchy: **Martin Marietta Materials Inc → Barton Sand & Gravel Co → MN Portable #6**

- 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:** Tiller Corp → MN Portable #6; 1983-03-01 to 2021-05-03; source msha-controller-operator-history
- **operator_operates_mine:** Barton Sand & Gravel Co → MN Portable #6; 1996-05-01 to current/open; source msha-controller-operator-history
- **controller_controls_operator:** Tiller Corp → Barton Sand & Gravel Co; 1996-05-01 to 2021-05-03; source msha-controller-operator-history
- **controller_controls_mine:** Martin Marietta Materials Inc → MN Portable #6; 2021-05-04 to current/open; source msha-controller-operator-history
- **controller_controls_operator:** Martin Marietta Materials Inc → Barton Sand & Gravel Co; 2021-05-04 to current/open; source msha-controller-operator-history