Robert Smithson’s “Spiral Jetty” on the shores of Great Salt Lake, in Utah, Feb. 27, 2008. Singer, a sculptor whose work, beginning in beaver bogs and pine forests and proceeding at an increasingly grander scale, eventually blurring the lines of art, landscaping, architecture and urban planning, died on March 14, 2024, at his home in Delray Beach, Fla. He was 78. (Tom Smart/The New York Times).