Firefighters labored with hand tools to dig a barrier around the last four to five miles of an uncontained fire front in Oregon's Siskiyou Mountains, where the biggest remaining blaze in the West has charred more than 83,000 acres.

"We have a rope around most of it, but the noose isn't pulled tight," fire information officer Ron DeHart said of the so-called Silver fire in the Siskiyou National Forest, west of Grants Pass.

An additional 1,000 acres were burned since Sunday in the Silver fire, much of it from blazes deliberately set by crews at containment lines to eliminate fuel ahead of the wildfire, he said.

The Silver fire, the largest remaining from a series of blazes that have scorched more than 1 million acres in seven Western states, has consumed 83,819 acres since it was ignited by lightning Aug. 30.

In the Klamath National Forest in Northern California, 1,500 firefighters battling the Yellow fire near uninhabited Forks-of-Salmon were hampered by thick smoke that cut visibility to 150 feet, U.S. Forest Service officials said.

The Yellow fire is one of two major fire areas that have blackened 62,800 acres in the Klamath, officials said.