18+ conservation programs in US or abroad for summer?

My daughter, who will be 18 in the spring, wants to do some type of immersive outdoor work this summer before she heads off to college. She's open to the US and abroad. I think her hope is to be outside all day, building or maintaining trails, etc. with other young adults around her age. She needs time off from academics and wants to be in nature and do some physical labor and maybe backpacking with others on days off. She's interested in programs abroad or in the states. She isn't interested in something pricey...she's happy to volunteer but does not want to have to pay a ton to do so. She's looking for something that lasts 4-6 weeks. Does anyone know of a conservation program similar to what I am describing? Any advice appreciated!