# Relationship history for MSHA mine 2102805

Current hierarchy: **Martin Marietta Materials Inc → Barton Sand & Gravel Co. → Reclamation Crew (Pfaff)**

- Valid-time bounds: inclusive, date granularity
- Null end: open-ended in the upstream history row; not independent proof of present control
- Transaction-time observation: 2026-10-17T05:35:58.500035+00:00

## Valid-time edges

- **controller_controls_mine:** Holm Norman D → Reclamation Crew (Pfaff); 1950-01-01 to current/open; source msha-controller-operator-history
- **operator_operates_mine:** H & S Asphalt Company → Reclamation Crew (Pfaff); 1980-06-01 to 1986-07-22; source msha-controller-operator-history
- **controller_controls_operator:** Holm Norman D → H & S Asphalt Company; 1980-06-01 to 1986-07-22; source msha-controller-operator-history
- **controller_controls_mine:** Tiller Corp → Reclamation Crew (Pfaff); 1983-03-01 to 2021-05-03; source msha-controller-operator-history
- **operator_operates_mine:** Barton Sand & Gravel Co. → Reclamation Crew (Pfaff); 1986-07-23 to current/open; source msha-controller-operator-history
- **controller_controls_operator:** Tiller Corp → Barton Sand & Gravel Co.; 1986-07-23 to 2021-05-03; source msha-controller-operator-history
- **controller_controls_mine:** Martin Marietta Materials Inc → Reclamation Crew (Pfaff); 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