In the Black Hills of South Dakota, less than a half-hour drive down the road from Mount Rushmore, just 17 miles away, another colossal mountain sculpture—the largest sculptural project in history—is taking shape. The Crazy Horse Memorial officially began taking shape in 1948. No one is predicting when it will be completed. Yet while it may be a work in progress with likely many years to go before it’s completed, it’s far enough along that already it’s a mesmerizing sight that draws more than a million visitors a year. A finished three-dimensional head of Crazy Horse stands at the peak of a 6,532-foot mountain silhouetted against the sky. The sculpture is truly massive; all four of Mount Rushmore’s gigantic presidential heads taken together could easily fit inside the head of Crazy Horse. From chin to top of forehead, it’s nearly nine stories—87 1/2 feet high, just over 58 feet wide. …