The 18 July blaze near Possum Kingdom Lake, about 70 miles (122kms) west of Fort Worth, destroyed five homes and took eight days to put out.
Chief Bonnie Watkins of the Possum Kingdom West Side Volunteer Fire Department said in a statement that she had traced the origin of the fire to a trash can packed with paper goods, food and glass bottles at an address in Hawkins Road.
She concluded that a wind gust had lifted the trash can’s lid, exposing the glass and paper to sunlight which “magnified through the glass bottles till it reached ignition temperature”.
“Once ignited the fire built rapidly. It vented out the side and top of the trash can causing nearby cedar trees to ignite,” Chief Watkins said.
â”This accidental fire could have been prevented simply by placing a large rock on the top of the trash can lid or by keeping all glass bottles separated in their own container,” she said.
Insurance Council of Texas spokesman Rich Johnson told the Associated Press he had never heard of wildfire starting that way.
“A fire started in a trash can is one thing, but one caused by sunlight magnified by glass bottles? That’s a new one,” Mr Johnson told the news agency.
Texas has been plagued by wildfires this month due to extreme drought, high temperatures over 100F (38C), and low humidity, exacerbated by the impact of the climate crisis.
A fire that began on Monday when grass caught fire in an open field and spread through a suburban Dallas subdivision destroyed nine homes.
Neighbours had complained that the field’s owner hadn’t cut the grass, which prompted a citation for a code violation.
A spark from a mower then ignited the tinder-dry grass, and a fire sped into the adjacent subdivision, damaging 26 homes, destroying nine of them, causing $6m in damage, the Associated Press reported.
A separate fire in Chalk Mountain 50 miles (80 kilometers) southwest of Fort Worth that has scorched 10.5 square miles (27 square kilometers) of North Texas, destroying 16 homes was 40 per cent contained by Thursday, fire officials said.