It’s one of the prettiest places in Southern California.An aerial shot of Lake Gregory in Crestline, California.Credit: Marcus Jones/Adobe StockKey PointsPerched in the mountains above the city of San Bernardino, Crestline, California offers a welcoming atmosphere and easy access to all kinds of outdoor activities.Fly down waterslides and hop on inflatables at Lake Gregory, an 84-acre manmade reservoir that’s the perfect place to cool off on hot…