Firefighters were joined Saturday by a helicopter and two tankers in their continuing battle against a 4,000 acre wild-land fire.

Although it had not threatened any structures, the 2-day-old blaze was presenting a host of challenges to firefighters, including gusting winds, soaring temperatures and jagged terrain up Mitchell Canyon.Kathy Jo Pollock of the Interagency Fire Center said late Saturday afternoon the fire was 50 percent contained.

Four hand crews were enduring "really really steep" terrain in their effort to extinguish the human-caused blaze in the remote section of Tooele County, Pollock said.

Although investigators had determined the fire was man-started, they are not sure of the exact cause.

Saturday's efforts were further hampered after the center released one of the air tankers to southern Utah, where a wildland fire had started near Cedar City, Pollock said.