GORMAN, Calif. — Authorities evacuated at least 1,200 people Saturday as a wildfire in Los Angeles County spread over thousands of acres near a major highway and threatened nearby structures, officials said.

The blaze, named the Post Fire, burned more than 3,600 acres (5.6 square miles or 14.5 square kilometers) near the Interstate 5 freeway in Gorman, about 62 miles (100 kilometers) northwest of Los Angeles, according to the California Department of Forestry and Fire Protection.

California State Park Services evacuated 1,200 people from the Hungry Valley recreation area in Gorman and both Hungry Valley and the Pyramid Lake reservoir were closed as a result of the fire threat, the Los Angeles County Fire Department said in an 8 p.m. update.

The flames broke out at around 1:45 p.m., authorities said.

The fire was moving southeast toward Pyramid Lake and crews were constructing perimeter fire lines while aircraft worked against limited visibility to stop the fire’s progress, the fire department said.