EUREKA, Calif. — President Barack Obama on Thursday expanded the territory of the California Coastal National Monument, adding six sites and more than 6,000 acres to the monument area that includes islets, reefs and rock outcroppings spanning much of the state’s coastline.

The new sites include areas from Orange County to Humboldt County. They are: Trinidad Head, Lighthouse Ranch and Lost Coast Headlands in Humboldt County; Coast Dairies in Santa Cruz County; Piedras Blancas in San Luis Obispo County; and many outcroppings and small islands off the Orange County coast.

President Bill Clinton created the national monument in 2000, and Obama expanded it once before in 2014.

“Today’s expansion will protect incredible coastal natural resources, scenic views, and areas of cultural and historical significance, including sites that provide insight into the Native peoples who first lived along California’s coast and places still important to local tribes today,” the White House said in a statement.

The new designation won praise from many California elected officials and environmental groups.

But the discussion over the potential monument status in recent months brought concern from people who live, farm or do both near some of the designated areas, including Coast Dairies and Lost Coast Headlands. They were worried especially about increased tourist traffic.

“I was raised there, and now we use it for our beef cattle,” Yvette Green said of Lost Coast Headlands, which is near Ferndale. “Our livelihoods are going to be affected by this.”

The areas are among several new national monuments Obama declared on Thursday. Most are civil rights sites in the South whose designation was timed to arrive near Martin Luther King Jr. Day.

He also expanded the Cascade-Siskiyou National Monument in southwest Oregon and Northern California.