A wildfire burning in the Francis Marion National Forest has grown to at least 800 acres with no containment, and the U.S. Forest Service is leading a federal-and-local firefight roughly 40 minutes north of Charleston. The blaze, named the Horse Island Fire, sits in the Lowcountry — not the Grand Strand — but it is burning under the same bone-dry conditions now gripping Horry County, where nearly the entire county sits in extreme drought. This d…