Yeah, this is the norm for the Cleveland National Forest. When I lived in Lake Elsinore, we would run up to Santiago all the time on a spur of the moment decision with nothing better to do. They shut down most of the roads up there during fire season, and again when the weather gets really bad during the late winter. There's really only a few months of the year that the area can be accessed.
Best to always keep an eye on the "current conditions" areas of the forest service websites, like Alex did, or call the ranger station/visit the ranger station in person, like Sir John of Fullerton did. Keeps you from unexpectedly running up on a locked gate and ruining your day, especially if you came from far away.