A wildfire burning in Yellowstone National Park's backcountry swelled from less than an acre to more than 1,160 acres between Wednesday and Saturday evening.The lightning-caused Spruce Fire is about 10 miles west of Fishing Bridge and two miles south of Hayden Valley in a remote, central portion of the park, the National Park Service says.

When Park Service personnel discovered the fire on Wednesday, they described it as about a tenth-of-an-acre and "creeping" through a wooded area.However, warmer temperatures and lower humidity allowed the fire to grow to roughly 425 acres by 11 a.m. Saturday and those conditions — plus some westerly winds — helped it nearly triple to an estimated 1,164 acres some seven hours later, the Park Service said.With conditions remaining dry, park officials expected the Spruce Fire to remain active, keep growing and to put out "a very visible smoke column" on Sunday."Although smoke from the fire is visible throughout the park and surrounding communities, no park facilities, structures, trails, or roads are threatened and there are no closures in place," the Park Service said in a Sunday morning news release.The Park Service said the Spruce Fire "continues to play its natural role in the ecosystem and is being managed for its benefits to park resources."Crews monitoring the fire by helicopter reported a typical mosaic pattern of burning in the lodgepole pine forest, with patchy burning inside the fire’s perimeter, isolated torching of single trees, and only a small amount of crowning when fire activity picked up on Saturday afternoon, the release said.The fire can be seen from a webcam at the Mount Washburn Fire Lookout:www.nps.gov/yell/learn/photosmultimedia/webcams.htm.

A much smaller fire, the 5L4 Fire on the Promontory Peninsula at the south end of Yellowstone Lake, was reported on Aug. 24, is currently 16 acres and not very active. Crews are also managing this fire for its benefits to park resources, the Park Service said. Backcountry campsites 5L3, 5L4, and 6A1 continue to be closed.The fire danger in Yellowstone National Park is currently listed as high. There are no fire restrictions in place, but campfires are only allowed in designated grills in park campgrounds, some picnic areas, and specific backcountry campsites.