Tracy Fire Department crews received a report about the fire near Grant Line and Naglee roads around 9:30 p.m.
The first firefighters at the scene found the middle of a haystack burning in a field north of Grant Line Road across from the Walmart shopping center, according to Andrew Kellogg, Tracy Fire Department division chief.
He said flames quickly spread and ignited all 2,942 bales of alfalfa that had been cut and stacked on Friday, April 26.
Kellogg said the entire haystack — valued at more than $44,000 — was a complete loss.
According to Kellogg, crews were also concerned smoke from the burning hay could act as an electrical conductor and cause an arc from two nearby power transmission towers to the ground.
Once firefighters determined the towers and power lines were not in danger, he said, crews tried to protect irrigation equipment and pipes near the haystack.
Grant Line Road was closed in both directions between Lammers Road and the west edge of the Walmart shopping center. Ash covered cars and the Walmart parking lot.
Division Chief Steve Hanlon said the cause of the fire was unknown, but said if the hay was wet when it was cut and baled the warm weekend temperatures could have led to spontaneous combustion inside the stack.
Crews were still pouring water on the burning bales at 11 p.m. Hanlon said the road would be open by 4:30 a.m. Monday.
• Contact Glenn Moore at 830-4252 or firstname.lastname@example.org.