Final answer:
National outdoor recreation planning efforts ceased during President Eisenhower's administration, marked by policies that reduced federal protection for natural lands and aimed for Native American assimilation.
Step-by-step explanation:
National outdoor recreation planning efforts and substantial progress in federal land conservation effectively concluded during President Eisenhower's administration. This was marked by the policy termed “termination”, which aimed for the rapid and complete assimilation of Native Americans into mainstream American society. This termination policy also involved an end to the special programs and funding for Native Americans in 1953, leading to the end of federal recognition of fourteen tribes between 1954 and 1960. While the conservation efforts under President Roosevelt were significant, with 148 million acres of forest reserves set aside and the establishment of more than 50 wildlife sanctuaries and several national parks, the Eisenhower administration shifted its focus away from land conservation and towards policies that were less favorable towards maintaining federal protection for these lands.