Tunnel collapse near Knights Ferry in Stanislaus County kills 1, injures 1

One person died and another was hospitalized after a tunnel collapse at a Stanislaus County construction site Tuesday, officials said.

It happened just before 3:45 p.m. at the Canyon Tunnel Project site, located northeast of Knights Ferry near Sonora and Schell roads, the South San Joaquin Irrigation District said.

Upon receiving the call about the incident, Modesto Fire officials said two people were believed to be trapped at the remote site.

The department said Tuesday evening that, when they arrived, one person was found injured outside the tunnel with minor to moderate injuries. A second person was still inside the tunnel and has been declared dead.

"Right now, we are formulating plans to recover that person," said Captain Joe Spani with Modesto Fire.

On Wednesday, the Calaveras County coroner's office identified the woman who died as 35-year-old Coulterville resident Twyla Capurro. A person who knew the victim said Capurro was a mother and worked for Provost & Pritchard Consulting.

Modesto Fire said the collapse happened about 200 feet into the tunnel. The site is on private property, an irrigation district spokesperson confirmed.

Stanislaus Consolidated Fire District crews responded along with Cal Fire, and officials from the Stanislaus and Calaveras sheriff's offices also assisted.

The Canyon Tunnel Project is a joint effort between the Oakdale Irrigation District and the South San Joaquin Irrigation District. The South San Joaquin Irrigation District said in a statement Wednesday afternoon, "All work on the project has been suspended at this time."

In a Spring 2026 update on the project posted to the South San Joaquin Irrigation District's YouTube channel just hours before the collapse, footage shows some of the tunneling work being done inside.

An unstable slope occasionally drops rock into a section of the current canal downstream from the Goodwin Dam that serves the two water districts. The Canyon Tunnel Project aims to bypass that section and provide a safer work environment and downstream reliability, according to the project's website. 

At this time, it is unclear what may have caused the collapse at the site.

Officials said the situation remains evolving and additional updates will be provided as they become available.