SARATOGA SPRINGS — With a fire-blackened field as a backdrop, Gov. Jon Huntsman Jr. warned Utahns on Tuesday of the dangerous fires that come from the negligent use of Utah's wild lands.

"It's only June and we've already seen 250 fires," Huntsman said, with the rubble of the recently ignited Mercer fire making his point behind him. "We figure that 61 of the 250 fires have been started by lightning, but the remainder are human-caused, which is exceedingly high. Because of that, we've all got to redouble our efforts in terms of understanding how these fires started."

The Mercer fire, named for its proximity to Mercer Canyon, is about 50 percent contained, fire officials said. The blaze has engulfed about 5,100 acres near Lake Mountain in Saratoga Springs since Monday, but efforts to douse the flames continued Tuesday evening. The fire was expected to be extinguished by Wednesday, according to the National Interagency Fire Center.

Elsewhere in the state, two other fires burned Tuesday — one in Spanish Fork Canyon and one about 45 miles west of the Great Salt Lake.

Representatives from the state fire marshal's office said the cause of the Mercer fire is under investigation, but it is assumed the fire was caused by humans. Most often, the wildfires that plague Utah's dry summers are caused by campfires, off-road vehicle use, target shooting and fireworks, the governor said.

"We have the Fourth of July around the corner and we have the 24th of July following that," Huntsman said. "This is the time when people get out and they camp and they light up fireworks and they get out in their SUVs and ride the trails. That's all fine, but we need to step up our sense of awareness and sensitivity about how these fires start."

According to Tracy Dunford, fire management officer for the state Division of Forestry, Fire and State Lands, off-road vehicles can cause wildfires if tall, dry grass is exposed to hot carburetors or sparks. Target shooting can cause fires if illegal ammunition is used or sparks are caused by shooting metal or rocks.

Utah's non-native, straw-like cheat grass is extremely flammable under the dry, hot conditions that currently beset the state. Those conditions are not unusual, but the high number of people causing fires this year is a concern.

The phenomenon is puzzling to Dunford.