The Rainbow fire burning along the northern boundary of Yellowstone National Park grew slightly since its discovery Monday but remained only about a half-acre in size.

Lightning from a Sunday thunderstorm started the fire on the north-facing slope of Sepulcher Mountain, uphill from Rainbow Lake, and below the Sepulcher Mountain Trail.

Yellowstone fire officials are monitoring the fire but allowing it to burn, because fire plays an important role in maintaining the health of the area's wildlife and vegetation.

The fire is well away from Mammoth Hot Springs, Gardiner and all roads and visitor services.

However, a smoke column or occasional flames from individually burning trees may be visible at times from the park's North Entrance Road, in Gardiner and from U.S. Highway 89 north of the park.

As a precaution, rangers have temporarily closed the Sepulcher Mountain Trail.

There have been 17 fires in Yellowstone this summer.