If you dig a little, you will see that there are a lot of cross associations.

Mr. Ara Marderosian is the executive director of Sequoia Forestkeepers, he is also the Secretary of the Kern Kaweah Sierra Club. Marderosian is also associated with Earth Island
http://www.martenlaw.com/newsletter/20090305-env-groups-rights-limited
http://www.kernkaweah.sierraclub.org/officers.html

Michael J. Connor, Ph.D. of the Western Watersheds Project has been associated with Sierra Club
http://www.energy.ca.gov/sitingcases/iva...ve_TN-52447.PDF

So maybe not the Sierra Club, but they certainly are all partying together.