We just received this press release:

For the 21st year, YA is collaborating with Yosemite Institute, the National Park Service, and DNC Parks & Resorts at Yosemite to bring you the Cooperative Work Weeks program. With support from DNC, YA volunteers join an NPS project leader and a Yosemite Institute naturalist for a week of restoration and revegetation work in locations throughout the park. Volunteers make a contribution to cover the cost of meals and program administration and work four days with a day off in the middle to rejuvenate and explore.

Here is more information about the program.