# Relationship history for MSHA mine 0504520

Current hierarchy: **Martin Marietta Materials Inc → Martin Marietta Materials, Inc → Northern Portable Plant #21**

- 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:** Martin Marietta Materials Inc → Northern Portable Plant #21; 1950-01-01 to current/open; source msha-controller-operator-history
- **controller_controls_mine:** Richard K  Stephenson et al → Northern Portable Plant #21; 1985-09-05 to current/open; source msha-controller-operator-history
- **operator_operates_mine:** Roaring Fork Aggregates Inc → Northern Portable Plant #21; 1993-06-01 to 2001-08-21; source msha-controller-operator-history
- **controller_controls_operator:** Richard K  Stephenson et al → Roaring Fork Aggregates Inc; 1993-06-01 to 2001-08-21; source msha-controller-operator-history
- **controller_controls_operator:** John C  Martin et al → Roaring Fork Aggregates Inc; 1993-06-01 to 2001-08-21; source msha-controller-operator-history
- **controller_controls_mine:** Lafarge S A → Northern Portable Plant #21; 1998-02-11 to current/open; source msha-controller-operator-history
- **operator_operates_mine:** Western Mobile Northern Inc → Northern Portable Plant #21; 2001-08-22 to 2002-01-30; source msha-controller-operator-history
- **controller_controls_operator:** Lafarge S A → Western Mobile Northern Inc; 2001-08-22 to 2002-01-30; source msha-controller-operator-history
- **operator_operates_mine:** Lafarge West Incorporated → Northern Portable Plant #21; 2002-01-31 to 2012-03-25; source msha-controller-operator-history
- **controller_controls_mine:** Lafarge S A → Northern Portable Plant #21; 2002-01-31 to 2015-07-09; source msha-controller-operator-history
- **controller_controls_operator:** Lafarge S A → Lafarge West Incorporated; 2002-01-31 to 2012-03-25; source msha-controller-operator-history
- **operator_operates_mine:** Martin Marietta Materials, Inc → Northern Portable Plant #21; 2012-03-26 to current/open; source msha-controller-operator-history
- **controller_controls_operator:** Martin Marietta Materials Inc → Martin Marietta Materials, Inc; 2012-03-26 to current/open; source msha-controller-operator-history
- **controller_controls_mine:** Holcim Ltd → Northern Portable Plant #21; 2015-07-10 to current/open; source msha-controller-operator-history
- **controller_controls_operator:** Holcim Ltd → Lafarge West Incorporated; 2015-07-10 to 2012-03-25; source msha-controller-operator-history