From Wikipedia

The Civilian Conservation Corps

The Civilian Conservation Corps (CCC) was a public work relief program for unemployed men age 18-24, providing unskilled manual labor related to the conservation and development of natural resources in rural areas of the United States from 1933 to 1942. As part of the New Deal legislation proposed by President Franklin D. Roosevelt (FDR), the CCC was designed to provide relief for unemployed youth who had a very hard time finding jobs during the Great Depression while implementing a general natural resource conservation program on public lands in every U.S. state, including the territories of Alaska, Hawaii, Puerto Rico, and the U.S. Virgin Islands.

During the time of the CCC, volunteers planted nearly 3 billion trees to help reforest America, constructed more than 800 parks nationwide that would become the start of most state parks, developed forest fire fighting methods, a network of thousands of miles of public roadways, and constructed buildings connecting the nation's public lands.