When and why did Effigy Mounds National Monument become part of the National Park Service?

Effigy Mounds National Monument was authorized on October 25, 1949, when President Harry Truman, using the provisions of the 1906 Antiquities Act, signed a proclamation declaring "the earth mounds in northeastern part of the State of Iowa known as the Effigy Mounds are of great scientific interest because of the variety of their forms, which include animal effigy, bird effigy, conical, and linear types, illustrative of a significant phase of the mound building culture of prehistoric American Indians". On May 27, 1961, an Act to include 272 new acres to the Monument added the mission to "protecting existing wildlife and other natural values. The authorization of the Monument was a culmination of a 40-year effort, interrupted by two world wars, to establish a national park along the upper Mississippi River in Iowa. A national parks movement was beginning to gain public support throughout the United States by the 1890s. As public interest in conservation and parks gained a foothold, ...  more