CASPER, Wyo. (AP) - A wildfire on Casper Mountain that's forced the evacuation of about 400 people has spread to between 5,000 and 6,000 acres. The Sheep Herder Hill Fire started Sunday afternoon and quickly spread as it jumped from tree to tree on the mountain that overlooks the city. About 150 structures and homes on the mountain's east side remained evacuated Monday, including the Crimson Dawn Museum. Natrona County Emergency Management Director Stew Anderson told KTWO-AM that he believes it's safe. So far he said firefighters have been mainly on the defensive. More crews were on their way and additional air support has also been requested. Authorities have confirmed that one structure has burned but fire managers say up to five may have been burned. The federal government says it will help with firefighting costs.