A wildfire sparked by a small-plane crash on a mountain outside of Reno had burned about 40 acres by Sunday evening as it crept toward the Mount Rose ski resort, fire officials said. The fire started at about 1:40 p.m. in a rugged, wooded area on Slide Mountain on the northwest side of the Washoe Valley, said Adam Mayberry, spokesman for the Truckee Meadows Fire Protection District. Witnesses reported seeing a small airplane crash in the area, causing an explosion, he added. The aircraft crashed in a forested area above Bowers Mansion. Medics tried to reach the area Sunday, but the crash site would not be accessible until Monday, said Ian Gregor, spokesman for the Federal Aviation Administration. Information on the number of people on board, their conditions, or the route of the aircraft was unknown Sunday. The blaze, dubbed the Slide Fire, initially threatened the Mount Rose ski area but had stopped advancing in that direction late in the afternoon, fire officials said.