Fire crews were battling a wildfire that started Thursday and forced a precautionary evacuation of a Boy Scout camp and cast a huge plume of smoke into the evening sky over Las Vegas. The fire quickly grew to more than 200 acres (81 hectares) on Potosi Mountain. It’s near the main highway between Las Vegas and rural Pahrump. A Clark County fire official says no structures were immediately in danger, no injuries were reported and the cause of the fire was not immediately known. Forecasters have warned of excessive heat this weekend, with temperatures climbing above 110 degrees.