Two lanes on Interstate 5 north of Castaic remained closed Tuesday night as firefighters tried to make sure a weakened 288-acre blaze near Pyramid Lake didn’t spring back to life, a U.S National Forest spokeswoman said.

The Osito Fire, which charred light grass and brush southeast of the Vista Del Lago exit on the I-5, had no active flames Tuesday afternoon, spokeswoman Dee Deckert said. But firefighters remained parked on the two right lanes of the northbound I-5 since the fire began Monday afternoon.

The blaze did not damage any structures or utilities, though it did briefly threaten gas, oil and power lines. Officials on Tuesday scaled down the size of the blaze from an initial estimate of more than 400 acres to 288 acres after a helicopter equipped with infrared cameras surveyed the burn area, Deckert said.

Officials expect to have the fire fully contained sometime Wednesday, she said.

The cause of the blaze was under investigation.