Exactly.
40°45'16.09"N
119°14'11.43"W
These are the coords for the festival. (Or, just go to Google Earth, look up Gerlach, NV, and scroll northeast a bit until you see the geometric shapes on the dry lakebed). Though it moved farther down the playa last year, it's pretty much been the same place for years--Black Rock Desert.
As you can see, there's nothing there but flat lakebed, or "playa". Even the road tracks are swept clean at the end of each festival. People fan out to pick up all trash, right down to specks of glitter, so nothing is left behind.
If you wanted to make sure geocachers had a loggable spot, you could set a cache in Gerlach. I'd suggest the famous water tower, which the Burning Man organization (BORG) has raised funds to preserve. Otherwise, simply post to the forum a clue (the name of your camp, a hint where to find coords for your cache, etc) and members who are going to the playa can play along. By the way, "Black Rock City" is now wireless, so you can post from there!
thanks for the coords - Gerlach is an excellent idea. you're a gem!