SAN DIEGO — Northern California homeowners allege in a lawsuit filed Tuesday that Pacific Gas & Electric Co. failed to adequately protect its power lines before the region’s deadly wildfires, a theory that state investigators are considering as they try to determine the cause.

The lawsuit in San Francisco Superior Court on behalf of Santa Rosa homeowners Wayne and Jennifer Harvell says drought-like conditions over the summer put fire dangers “at an extraordinarily high level,” particularly after heavy winter rains increased vegetation. It says PG&E failed to trim and remove vegetation as it should have.

PG&E Corp., the utility’s parent company, said Friday that the California Department of Forestry and Fire Protection was investigating its power lines and equipment as a possible cause of the fires that have killed at least 41 people and destroyed 6,000 homes.

The California Public Utilities Commission, which regulates PG&E, would investigate only if state fire investigators determine that that the utility’s equipment is suspected as a cause. That could lead to significant fines and penalties.

The San Francisco-based utility said it would not speculate on causes of the fire and that it was cooperating with investigators.

PG&E says it has told state regulators of seven incidents of damage to its equipment, including downed power lines and broken poles. It did not say whether they may have caused or contributed to the fire.

Gerald Singleton, an attorney representing other homeowners and renters, said winds were strong but PG&E should have anticipated them.

“We can’t get rid of all possible risks,” he said. “It really is based on reasonableness — and that is what their duty is.”

PG&E shares jumped 7.5 percent, or $4.01, to close at $57.44 on the New York Stock Exchange on Tuesday. Still, the shares are down 17 percent since Wednesday.

Earlier this year, the utility commission fined PG&E $8.3 million for failing to maintain a power line that sparked a massive blaze in Northern California that destroyed 549 homes and killed two people. A state fire investigation found the utility and its contractors failed to maintain a gray pine tree that slumped into a power line igniting the September 2015 fire in Amador County.

Previously, California regulators fined PG&E $1.6 billion for 2010 natural gas explosion in the San Francisco Bay Area city of San Bruno that killed eight people and destroyed 38 homes.

Also Tuesday, U.S. Sens. Dianne Feinstein and Kamala Harris of California wrote the Federal Communications Commission to express concern that the federal government has yet to adopt rules that would require wireless carriers to more precisely target neighborhoods with orders to evacuate. As fires rapidly spread Oct. 8, authorities sought to avoid alarming unaffected residents.

“These emergency services are caught in a bind between notifying individuals in imminent danger and risking mass panic. As a result, these services are compelled to rely on emergency messaging systems with far less reach and far less capacity,” they wrote.