Two radio transformers were threatened by grass fires ignited by electrical shorts Friday afternoon on Ensign Peak in northern Salt Lake County.

About 10 acres of grasslands was destroyed by the two blazes, which were started when a Utah Power & Light Co. service line shorted. The line provides power to several radio and television facilities on the peak.Salt Lake City Fire Battalion Chief Tom Tallon said the blazes were spotted about 5:15 p.m. by a Utah Highway Patrol helicopter. At first, officials suspected arson because vehicles were spotted in the area, but a subsequent investigation pinpointed the power line.

The fire on the lower part of the peak was contained within about one hour and consumed about three acres, Tallon said. Damage could have been more severe, however, as firefighters thought the blaze was out and were mopping up in the area when firemen noticed that the fire was still burning on the other side of a small ravine. A second unit was summoned to help contain that blaze.

The upper blaze threatened radio dispatch transformers owned by the UHP and Salt Lake City. Tallon said two water drops by the U.S. Forest Service helped firefighters, and the facilities were not damaged. The fires were out at 8:30 p.m. The upper fire blackened about seven acres.

Crews from Salt Lake City, the interagency fire center and the Salt Lake City Water Department responded. About 24 firefighters and nine pieces of equipment were used.