Two fires burning inside the Bob Marshall Wilderness are sending smoke into the Flathead Valley and are expected to grow this week. The largest - a fire of unknown cause first detected near Big Salmon Lake on Aug. 16 - quickly grew to about 2,750 acres by presstime.

The trail to Big Salmon Lake, a well-used access into the wilderness for packers over Holland Pass, and the Lime Creek trail were closed. Structure protection efforts were planned for the Salmon Forks cabin, Salmon Forks suspension bridge and the Little Salmon Bridge.

Meanwhile, the lightning-caused Hammer Creek Fire continues to burn along the South Fork Flathead River about 2 1/2 miles north of the Big Prairie Ranger Station. It grew to about 500 acres by Aug. 18 as a result of dry, warm weather and gusty winds before settling down over the weekend. By presstime, it covered 1,350 acres.

The Hammer Creek Fire is being allowed to burn to the east for resource benefits in the wilderness. Suppression actions have been necessary to keep the fire from crossing to the west side of the South Fork River, which could force the closure of a busy trail. The trail on the east side of the South Fork was closed north of Big Prairie, and structure protection measures were taken at the Big Prairie Ranger Station and a nearby pack bridge.

Outside the wilderness, the human-caused South Fork Lost Creek Fire gained ground in steep, forested terrain seven miles southeast of the community of Swan Lake. The fire grew to more than 1,200 acres and was 35 percent contained by presstime.

Firefighters were successful in cutting fire lines along the west and south flanks last week, and a helicopter with a torch was used for a burn-out operation on steep terrain on the fire's southeast perimeter.