The California Highway Patrol is looking into the inspection history of the dump truck that backed over and killed a construction employee and pinned his co-worker on Highway 17 near Scotts Valley in Santa Cruz County, a tragedy that has devastated their employer, one of California’s oldest and largest construction companies.

The CHP investigation into the death of 54-year-old Robert Gill and the serious injury to 33-year-old Stephen Whitmire is also focusing on whether the truck had working backup warning alarms at the time, according to CHP officer Trista Drake.

Drake said that the CHP inspected the truck in the hours after the incident and has interviewed witnesses, including the unidentified truck driver, but did not plan on releasing its investigative results any time soon.

Gill and Whitmire were doing contract work for Caltrans, helping to remove a mudslide from the highway so the agency could reopen the road to drivers.

Investigators believe the truck was backing up toward a hill when the workers were hit, Drake said. Gill was pronounced dead at the scene.

Whitmire was found pinned underneath the rear of the truck when CHP crews arrived, Drake said. Rescuers extricated him and took him by ambulance to a local hospital, conscious and talking at the time, she said. He is believed to be in stable condition.

Both men were employed by Watsonville-based Graniterock, a 117-year-old family-owned construction materials and services company, which holds offices and does work in the San Francisco and Monterey Bay areas.

The firm has deep history with California. Graniterock got its license from the Contractors State License Board in 1929, one of the first companies to do so, according to agency spokesman Rick Lopes.

The nearly 1,000 workers there are reeling, according to Shanna Crigger, spokeswoman for Graniterock.

“We are all mourning. We are all in a state of shock,” Crigger said. “We are struggling to come to terms with losing someone who was just an incredible person and incredible team member.”

Along with the CHP, California’s Division of Occupational Safety and Health — Cal/OSHA — has opened an investigation into the incident, agency spokesman Erika Monterroza said.

Graniterock has set up an online fundraiser for Gill’s wife and two children.