Boulder County Parks and Open Spaces closed Wednesday morning in response to extreme danger from the CalWood fire and a new red flag warning.

The CalWood fire began Saturday, quickly growing to 9,915 acres as of Wednesday morning. The fire is 21% contained.

Boulder County closed several properties to public use, including the Anne U. White trail, Bald Mountain, Caribou Ranch, Castle Rock climbing area, Grassy Top Park, Hall Ranch, Heil Valley Ranch, Hessie trailhead, Mud Lake, Reynolds Ranch, Sugarloaf Mountain and the Fourth of July trailhead.

The U.S. Forest Service also closed all National Forest land in Clear Creek, Jefferson, Gilpin, Boulder and Larimer counties on Wednesday.

The closures will be re-evaluated daily as conditions change.

At least 26 houses in the foothills northwest of Boulder have been damaged by the CalWood fire and about 3,000 people have been evacuated.

The red flag warning is in effect from noon Wednesday until 8 a.m. Thursday as a result of high winds and low humidity.

Officials said they plan to continue to build a fire line on all edges of the fire Wednesday as the fire backs down toward Spruce Gulch.

Crews will work to protect structures in the Balarat area.