CRAZY HORSE, S.D. — It was to be the largest sculpture in the world: a granite portrait of a Sioux leader on horseback whittled out of a mountain in the Black Hills here. In scale and complexity, the carving would dwarf the imposing collection of presidential profiles on nearby Mount Rushmore.

As he started the Crazy Horse monument in 1947, short on money, manpower and the credulity of just about anyone who heard his plans, Korczak Ziolkowski, a sculptor from Connecticut, promised the tribal leaders who had recruited him and the local residents who scorned him that he was dedicating his life to the effort.

But he underestimated the scale of the undertaking. His promise, it turned out, was a multigenerational commitment.

The sprawling country clan Mr. Ziolkowski reared at the base of the mountain has spent the 30 years since his death honoring his final plea to continue the effort, to which he supposedly added, “But go slowly, so you do it right.”