From 1933 to 1942, hundreds of thousands of unemployed young men became part of a federal work initiative called Civilian Conservation Corps. The CCC's work in Pennsylvania transformed the state's forests and parks. CCC was made up of groups of men who were issued uniforms, given three meals a day and paid a monthly stipend. According to DCNR, here in PA they helped to plant trees, build roads in parks and fight forest fires.
Specifically, CCC labor is said to have helped build Blue Knob, Hickory Run, French Creek, Laurel Hill and Raccoon Creek. All parks that were eventually given to the Commonwealth and became state parks. There's a lot to learn about the CCC. A museum remains at Promised Land state park in Pike County, and you'll find an interpretive center at Parker Dam State Park in Clearfield County, with artifacts and displays about what state officials call the valuable work done that is still enjoyed today.