Approximately 40 firefighters spent almost five hours battling a fire in a 200-ton haystack early Tuesday that investigators believe was the work of an arsonist.

Riverton volunteer firefighters were already on the scene of a another haystack fire near 12300 South and 1300 West when a motorist driving on I-15 reported a larger blaze at Withers Dairy, 12900 S. 1300 West.Salt Lake County Fire Lt. Dennis Steadman said the motorist spotted the larger blaze from more than five miles away and reported the fire at 1:34 a.m. The first firefighters responding said flames were leaping 25 to 35 feet above the haystack.

Riverton firefighters called for help from the county, Draper, South Jordan and Murray. Front-end loaders were also called in to break up the burning hay bales. "You practically have to break each bale apart and hose it down to get the fire out," Steadman said.

No buildings were damaged in either fire, but the loss at the dairy is estimated at $9,000.Steadman said nine to 12 similar fires have been reported recently in Utah County and that officials believe they may be tied to the two Tuesday fires in Riverton.

Blazes have occurred in the unincorporated county, Lehi, Pleasant Grove, Lindon, Orem and Payson. Utah County Fire Marshal Tom Wroe said fires charred structures or hay in one of those areas nearly every night since last Monday - including three fires in Orem and Pleasant Grove Sunday.

A barn fire in Orem at 1500 S. Sandhill Road destroyed about $10,000 worth of property. Other blazes have done damage ranging from hundreds to thousands of dollars, officials said.

Officials sent out an attempt-to-locate broadcast Tuesday for a two-tone Chevrolet pickup truck, 1973 or newer, that is darker on top - possibly brown. The truck is also reported to have a loud exhaust system.

A corrections officer at the Utah State Prison had seen a truck with two occupants that matched that description just minutes before the broadcast but was then unable to find the truck.