Hundreds of volunteers are joining state forestry officials in a massive tree-planting project at the Flight 93 National Memorial.

About 22,000 seedlings will be planted Friday and Saturday in western Pennsylvania, according to the Department of Conservation and Natural Resources.

United Flight 93 crashed in an abandoned strip mine in Shanksville after being hijacked by four terrorists on 9/11. Forty people died, along with the hijackers.

The seedlings are being planted over 32 acres within the site. Organizers hope to reforest the entire site with more than 150,000 trees.

The memorial located 65 miles southeast of Pittsburgh is still under construction. The National Park Service website estimates the visitors center will open later this year.